On Mon, 20 Feb 2006 18:13:22 -0500, "Bob" <bobsjunkmail@bellsouth.net>
wrote:

>
>"Mike Marlow" <mmarlowREMOVE@alltel.net> wrote in message
>news:dea96$43f9b46f$4528960b$13829@ALLTEL.NET.. .
>>
>> "Bob" <bobsjunkmail@bellsouth.net> wrote in message
>> news:jaiKf.20641$bW.19251@bignews8.bellsouth.net.. .
>>>
>>> <sycore@bellsouth.net> wrote in message
>>> news:kSbKf.20004$bW.11031@bignews8.bellsouth.net.. .
>>> > it is the 2.7L v6 engine.
>>> > I have a multimeter and can do the basics, but i am not the advanced in
>>> > testing.
>>> > The fuse pops about 3-4 seconds after i turn the ignition key to on
>>> > position.
>>> > I can easily unplug all of the sesors except maybe the canister close
>>> > valve.
>>> > Can i just plug them back in one at a time until it pops?
>>>
>>> 3-4 seconds means no "hard" short. You can try that, but without quite a
>> bit
>>> of electrical troubleshooting experience, you can get in over your head
>>> pretty quickly.
>>>
>>>
>>
>> I don't know what the schematics show for this circuit Bob, but he'd
>> likely
>> be ok at least trying this approach - assuming that the circuit does
>> really
>> consist of the components the OP first indicated.
>>
>> You're right that 3-4 seconds implies a short with a resistance and not a
>> direct short., and that kind of troubleshooting with a meter can get
>> confusing for folks who are not a little experienced. Depending upon how
>> the meter is set, it can potentially either look like a direct short
>> (leading to replacing the wrong component in vain), or not even show the
>> short (leading to the obvious oversight).
>>
>> I think in this case - again, assuming the circuit is as described, just
>> go
>> ahead as the OP suggests and disconnect the loads and selectively
>> re-connect
>> them. The caution with this technique is to make sure to inspect the
>> wiring
>> as well as the components.
>>
>> Over his head pretty quickly??? Hell - every time I get into
>> troubleshooting automobile wiring/electronics I make the same statement -
>> "I
>> hate working on car wiring". But... I do it, and I've been doing it a
>> long
>> time, so I understand this stuff pretty well, but I still hate it!
>>
>> --
>>
>> -Mike-
>> mmarlowREMOVE@alltel.net
>>
>What concerns me is given that there's a delay before the fuse blows, and
>wiring at 12 volts typically can't fail in a way that gives a high
>resistance short that's hard enough that it blows a fuse. If it were a high
>resistance short, he'd be dissipating about 240 watts (~12 volts at ~20 amps
>to blow a 10 amp fuse in a short but not instant time) at that high
>resistance point - much smoke would be present. The other possibility is a
>motion induced hard short to ground. If he in fact has something that is
>driven - a valve, etc - that has a short, and there's a delay before that
>device is actuated, he runs the possibility of damaging the driver. I mean,
>how many times can an output take a short before failing. To try to explain
>to use a current limiting device in place of a fuse for troubleshooting - a
>lamp, etc.- and what the results should be is really difficult.
>

I disagree. If it's a 10A circuit the normal load would be
~12/10=1.2 ohm. It's going to look like a short to anything but a
specialty resistance measuring circuit. I doubt it's really that low
and it is not that low per sensor so measuring may locate the bad
sensor. I would expect something like a 50% safety factor on the fuse
so I'd expect an agregate load of ~2.4 ohms. Each individual load
will be over that. Possibly well over that. If the circuit wiring is
properly sized it will not smoke with that load. I have seen
connectors with an ohm or more in a bad connection.

Polarity probably will also be an issue. You are going to need to use
the positive voltage resistance lead on the power lead to the sensor.
If you are not sure what one that is use a second meter set to measure
voltage and measure the voltage accross the probes of your resistance
meter.

Once You know the polarity probe the leads to the sensors with any
ground lead connected to the chassis. I bet several will be over 100
ohms so you can discount them for a first pass. If one is clearly
below 2 or 3 ohms it is probably the problem. If all of them look OK
then it is probably a function of the sensor activating and drawing
too much current. The easiest way to find that will be to disconnect
all of them then reconnect one at a time. You can either wait for the
fuse to blow or connect an ammeter accross a blown fuse. Monitor the
current draw as each sensor is connected. If I was doing this much
that is what I would start with. ;-)

If the fuse is blowing with the key on but not cranking the engine I
bet you will find the answer fairly easily. You probaly have a blown
semiconductor junction. It still has resistance, as does the
packaging leads, but it's well below what it should be.

nothermark

 

"nothermark" <trash@gnomex.cotse.net> wrote in message
news:vmnkv1l91d5i3snquafabfpojhvrga86g2@4ax.com...

> I disagree. If it's a 10A circuit the normal load would be
> ~12/10=1.2 ohm. It's going to look like a short to anything but a
> specialty resistance measuring circuit. I doubt it's really that low
> and it is not that low per sensor so measuring may locate the bad
> sensor. I would expect something like a 50% safety factor on the fuse
> so I'd expect an agregate load of ~2.4 ohms. Each individual load
> will be over that. Possibly well over that. If the circuit wiring is
> properly sized it will not smoke with that load. I have seen
> connectors with an ohm or more in a bad connection.
I'm not talking about burning the wire. A properly sized fuse will open
prior to the wiring heating significantly. What I am concerned with - if it
is a wiring issue - is that the point where the wire is being grounded, and
whatever the path to ground is is dropping the entire battery voltage over
what is likely a small area. According to the fusing tables, you need 15
amps of current to blow a 10 amp fuse in 4 seconds. So, the entire
dissipation over the wire and the short to ground is 12v * 15a = 180 watts.
15 amps would be a total resistance to ground of .8 ohms. If he looks at O2
sensors, they start out as fairly low resistance, so that may be a little
misleading.

>
> Polarity probably will also be an issue. You are going to need to use
> the positive voltage resistance lead on the power lead to the sensor.
> If you are not sure what one that is use a second meter set to measure
> voltage and measure the voltage accross the probes of your resistance
> meter.

If he's got a digital meter, most of them will not forward bias any diodes
present in things like position sensors, so he won't even see them. They are
not likely culprits anyway.

> Once You know the polarity probe the leads to the sensors with any
> ground lead connected to the chassis. I bet several will be over 100
> ohms so you can discount them for a first pass. If one is clearly
> below 2 or 3 ohms it is probably the problem. If all of them look OK
> then it is probably a function of the sensor activating and drawing
> too much current. The easiest way to find that will be to disconnect
> all of them then reconnect one at a time. You can either wait for the
> fuse to blow or connect an ammeter across a blown fuse. Monitor the
> current draw as each sensor is connected. If I was doing this much
> that is what I would start with. ;-)

If he puts an ammeter (like the one in his meter) across the open fuse,
he'll either cook his meter, or blow the current fuse in it (if there is
one).
Something that works well - if you don't have access to a current limited
power supply - is to use a high current lamp - like one or both filaments in
a 60 watt headlamp - in place of the fuse. Low current flow = no heating of
filament, so little drop across it. Short to ground = light lights, and
current is limited to about 5 amps for one filament, or about 10 amps for 2
in parallel. In either case, you can start disconnecting (or connecting)
things and watch continuously for what changes.


> If the fuse is blowing with the key on but not cranking the engine I
> bet you will find the answer fairly easily. You probaly have a blown
> semiconductor junction. It still has resistance, as does the
> packaging leads, but it's well below what it should be.
>
> nothermark

 

"nothermark" <trash@gnomex.cotse.net> wrote in message
news:vmnkv1l91d5i3snquafabfpojhvrga86g2@4ax.com...

> I disagree. If it's a 10A circuit the normal load would be
> ~12/10=1.2 ohm. It's going to look like a short to anything but a
> specialty resistance measuring circuit. I doubt it's really that low
> and it is not that low per sensor so measuring may locate the bad
> sensor. I would expect something like a 50% safety factor on the fuse
> so I'd expect an agregate load of ~2.4 ohms. Each individual load
> will be over that. Possibly well over that. If the circuit wiring is
> properly sized it will not smoke with that load. I have seen
> connectors with an ohm or more in a bad connection.
I'm not talking about burning the wire. A properly sized fuse will open
prior to the wiring heating significantly. What I am concerned with - if it
is a wiring issue - is that the point where the wire is being grounded, and
whatever the path to ground is is dropping the entire battery voltage over
what is likely a small area. According to the fusing tables, you need 15
amps of current to blow a 10 amp fuse in 4 seconds. So, the entire
dissipation over the wire and the short to ground is 12v * 15a = 180 watts.
15 amps would be a total resistance to ground of .8 ohms. If he looks at O2
sensors, they start out as fairly low resistance, so that may be a little
misleading.

>
> Polarity probably will also be an issue. You are going to need to use
> the positive voltage resistance lead on the power lead to the sensor.
> If you are not sure what one that is use a second meter set to measure
> voltage and measure the voltage accross the probes of your resistance
> meter.

If he's got a digital meter, most of them will not forward bias any diodes
present in things like position sensors, so he won't even see them. They are
not likely culprits anyway.

> Once You know the polarity probe the leads to the sensors with any
> ground lead connected to the chassis. I bet several will be over 100
> ohms so you can discount them for a first pass. If one is clearly
> below 2 or 3 ohms it is probably the problem. If all of them look OK
> then it is probably a function of the sensor activating and drawing
> too much current. The easiest way to find that will be to disconnect
> all of them then reconnect one at a time. You can either wait for the
> fuse to blow or connect an ammeter across a blown fuse. Monitor the
> current draw as each sensor is connected. If I was doing this much
> that is what I would start with. ;-)

If he puts an ammeter (like the one in his meter) across the open fuse,
he'll either cook his meter, or blow the current fuse in it (if there is
one).
Something that works well - if you don't have access to a current limited
power supply - is to use a high current lamp - like one or both filaments in
a 60 watt headlamp - in place of the fuse. Low current flow = no heating of
filament, so little drop across it. Short to ground = light lights, and
current is limited to about 5 amps for one filament, or about 10 amps for 2
in parallel. In either case, you can start disconnecting (or connecting)
things and watch continuously for what changes.


> If the fuse is blowing with the key on but not cranking the engine I
> bet you will find the answer fairly easily. You probaly have a blown
> semiconductor junction. It still has resistance, as does the
> packaging leads, but it's well below what it should be.
>
> nothermark

 

"nothermark" <trash@gnomex.cotse.net> wrote in message
news:vmnkv1l91d5i3snquafabfpojhvrga86g2@4ax.com...

> I disagree. If it's a 10A circuit the normal load would be
> ~12/10=1.2 ohm. It's going to look like a short to anything but a
> specialty resistance measuring circuit. I doubt it's really that low
> and it is not that low per sensor so measuring may locate the bad
> sensor. I would expect something like a 50% safety factor on the fuse
> so I'd expect an agregate load of ~2.4 ohms. Each individual load
> will be over that. Possibly well over that. If the circuit wiring is
> properly sized it will not smoke with that load. I have seen
> connectors with an ohm or more in a bad connection.
I'm not talking about burning the wire. A properly sized fuse will open
prior to the wiring heating significantly. What I am concerned with - if it
is a wiring issue - is that the point where the wire is being grounded, and
whatever the path to ground is is dropping the entire battery voltage over
what is likely a small area. According to the fusing tables, you need 15
amps of current to blow a 10 amp fuse in 4 seconds. So, the entire
dissipation over the wire and the short to ground is 12v * 15a = 180 watts.
15 amps would be a total resistance to ground of .8 ohms. If he looks at O2
sensors, they start out as fairly low resistance, so that may be a little
misleading.

>
> Polarity probably will also be an issue. You are going to need to use
> the positive voltage resistance lead on the power lead to the sensor.
> If you are not sure what one that is use a second meter set to measure
> voltage and measure the voltage accross the probes of your resistance
> meter.

If he's got a digital meter, most of them will not forward bias any diodes
present in things like position sensors, so he won't even see them. They are
not likely culprits anyway.

> Once You know the polarity probe the leads to the sensors with any
> ground lead connected to the chassis. I bet several will be over 100
> ohms so you can discount them for a first pass. If one is clearly
> below 2 or 3 ohms it is probably the problem. If all of them look OK
> then it is probably a function of the sensor activating and drawing
> too much current. The easiest way to find that will be to disconnect
> all of them then reconnect one at a time. You can either wait for the
> fuse to blow or connect an ammeter across a blown fuse. Monitor the
> current draw as each sensor is connected. If I was doing this much
> that is what I would start with. ;-)

If he puts an ammeter (like the one in his meter) across the open fuse,
he'll either cook his meter, or blow the current fuse in it (if there is
one).
Something that works well - if you don't have access to a current limited
power supply - is to use a high current lamp - like one or both filaments in
a 60 watt headlamp - in place of the fuse. Low current flow = no heating of
filament, so little drop across it. Short to ground = light lights, and
current is limited to about 5 amps for one filament, or about 10 amps for 2
in parallel. In either case, you can start disconnecting (or connecting)
things and watch continuously for what changes.


> If the fuse is blowing with the key on but not cranking the engine I
> bet you will find the answer fairly easily. You probaly have a blown
> semiconductor junction. It still has resistance, as does the
> packaging leads, but it's well below what it should be.
>
> nothermark

 

"nothermark" <trash@gnomex.cotse.net> wrote in message
news:vmnkv1l91d5i3snquafabfpojhvrga86g2@4ax.com...
> On Mon, 20 Feb 2006 18:13:22 -0500, "Bob" <bobsjunkmail@bellsouth.net>
> wrote:
>
> >
> >"Mike Marlow" <mmarlowREMOVE@alltel.net> wrote in message
> >news:dea96$43f9b46f$4528960b$13829@ALLTEL.NET.. .
> >>
> >> "Bob" <bobsjunkmail@bellsouth.net> wrote in message
> >> news:jaiKf.20641$bW.19251@bignews8.bellsouth.net.. .
> >>>
> >>> <sycore@bellsouth.net> wrote in message
> >>> news:kSbKf.20004$bW.11031@bignews8.bellsouth.net.. .
> >>> > it is the 2.7L v6 engine.
> >>> > I have a multimeter and can do the basics, but i am not the advanced
in
> >>> > testing.
> >>> > The fuse pops about 3-4 seconds after i turn the ignition key to on
> >>> > position.
> >>> > I can easily unplug all of the sesors except maybe the canister
close
> >>> > valve.
> >>> > Can i just plug them back in one at a time until it pops?
> >>>
> >>> 3-4 seconds means no "hard" short. You can try that, but without quite
a
> >> bit
> >>> of electrical troubleshooting experience, you can get in over your
head
> >>> pretty quickly.
> >>>
> >>>
> >>
> >> I don't know what the schematics show for this circuit Bob, but he'd
> >> likely
> >> be ok at least trying this approach - assuming that the circuit does
> >> really
> >> consist of the components the OP first indicated.
> >>
> >> You're right that 3-4 seconds implies a short with a resistance and not
a
> >> direct short., and that kind of troubleshooting with a meter can get
> >> confusing for folks who are not a little experienced. Depending upon
how
> >> the meter is set, it can potentially either look like a direct short
> >> (leading to replacing the wrong component in vain), or not even show
the
> >> short (leading to the obvious oversight).
> >>
> >> I think in this case - again, assuming the circuit is as described,
just
> >> go
> >> ahead as the OP suggests and disconnect the loads and selectively
> >> re-connect
> >> them. The caution with this technique is to make sure to inspect the
> >> wiring
> >> as well as the components.
> >>
> >> Over his head pretty quickly??? Hell - every time I get into
> >> troubleshooting automobile wiring/electronics I make the same
statement -
> >> "I
> >> hate working on car wiring". But... I do it, and I've been doing it a
> >> long
> >> time, so I understand this stuff pretty well, but I still hate it!
> >>
> >> --
> >>
> >> -Mike-
> >> mmarlowREMOVE@alltel.net
> >>
> >What concerns me is given that there's a delay before the fuse blows, and
> >wiring at 12 volts typically can't fail in a way that gives a high
> >resistance short that's hard enough that it blows a fuse. If it were a
high
> >resistance short, he'd be dissipating about 240 watts (~12 volts at ~20
amps
> >to blow a 10 amp fuse in a short but not instant time) at that high
> >resistance point - much smoke would be present. The other possibility is
a
> >motion induced hard short to ground. If he in fact has something that is
> >driven - a valve, etc - that has a short, and there's a delay before that
> >device is actuated, he runs the possibility of damaging the driver. I
mean,
> >how many times can an output take a short before failing. To try to
explain
> >to use a current limiting device in place of a fuse for troubleshooting -
a
> >lamp, etc.- and what the results should be is really difficult.
> >
>
> I disagree. If it's a 10A circuit the normal load would be
> ~12/10=1.2 ohm. It's going to look like a short to anything but a
> specialty resistance measuring circuit. I doubt it's really that low
> and it is not that low per sensor so measuring may locate the bad
> sensor. I would expect something like a 50% safety factor on the fuse
> so I'd expect an agregate load of ~2.4 ohms. Each individual load
> will be over that. Possibly well over that. If the circuit wiring is
> properly sized it will not smoke with that load. I have seen
> connectors with an ohm or more in a bad connection.
>
> Polarity probably will also be an issue. You are going to need to use
> the positive voltage resistance lead on the power lead to the sensor.
> If you are not sure what one that is use a second meter set to measure
> voltage and measure the voltage accross the probes of your resistance
> meter.
>
> Once You know the polarity probe the leads to the sensors with any
> ground lead connected to the chassis. I bet several will be over 100
> ohms so you can discount them for a first pass. If one is clearly
> below 2 or 3 ohms it is probably the problem. If all of them look OK
> then it is probably a function of the sensor activating and drawing
> too much current. The easiest way to find that will be to disconnect
> all of them then reconnect one at a time. You can either wait for the
> fuse to blow or connect an ammeter accross a blown fuse. Monitor the
> current draw as each sensor is connected. If I was doing this much
> that is what I would start with. ;-)
>
> If the fuse is blowing with the key on but not cranking the engine I
> bet you will find the answer fairly easily. You probaly have a blown
> semiconductor junction. It still has resistance, as does the
> packaging leads, but it's well below what it should be.
>
> nothermark

Ok, I unplugged all the sensors except the the canister close valve by the
fuel tank and canister purge valve under the throttle body. I turned on the
key and measured the current without the fuse in and it read 12.8
Then as soon as i put the fuse in it popped. I should mention the the car
was hit from behind recently enought to damage the rear bumper and
taillight.
Have to leave town tomorrow but will try some of the things suggested.

Thanks for all your help.

 

"nothermark" <trash@gnomex.cotse.net> wrote in message
news:vmnkv1l91d5i3snquafabfpojhvrga86g2@4ax.com...
> On Mon, 20 Feb 2006 18:13:22 -0500, "Bob" <bobsjunkmail@bellsouth.net>
> wrote:
>
> >
> >"Mike Marlow" <mmarlowREMOVE@alltel.net> wrote in message
> >news:dea96$43f9b46f$4528960b$13829@ALLTEL.NET.. .
> >>
> >> "Bob" <bobsjunkmail@bellsouth.net> wrote in message
> >> news:jaiKf.20641$bW.19251@bignews8.bellsouth.net.. .
> >>>
> >>> <sycore@bellsouth.net> wrote in message
> >>> news:kSbKf.20004$bW.11031@bignews8.bellsouth.net.. .
> >>> > it is the 2.7L v6 engine.
> >>> > I have a multimeter and can do the basics, but i am not the advanced
in
> >>> > testing.
> >>> > The fuse pops about 3-4 seconds after i turn the ignition key to on
> >>> > position.
> >>> > I can easily unplug all of the sesors except maybe the canister
close
> >>> > valve.
> >>> > Can i just plug them back in one at a time until it pops?
> >>>
> >>> 3-4 seconds means no "hard" short. You can try that, but without quite
a
> >> bit
> >>> of electrical troubleshooting experience, you can get in over your
head
> >>> pretty quickly.
> >>>
> >>>
> >>
> >> I don't know what the schematics show for this circuit Bob, but he'd
> >> likely
> >> be ok at least trying this approach - assuming that the circuit does
> >> really
> >> consist of the components the OP first indicated.
> >>
> >> You're right that 3-4 seconds implies a short with a resistance and not
a
> >> direct short., and that kind of troubleshooting with a meter can get
> >> confusing for folks who are not a little experienced. Depending upon
how
> >> the meter is set, it can potentially either look like a direct short
> >> (leading to replacing the wrong component in vain), or not even show
the
> >> short (leading to the obvious oversight).
> >>
> >> I think in this case - again, assuming the circuit is as described,
just
> >> go
> >> ahead as the OP suggests and disconnect the loads and selectively
> >> re-connect
> >> them. The caution with this technique is to make sure to inspect the
> >> wiring
> >> as well as the components.
> >>
> >> Over his head pretty quickly??? Hell - every time I get into
> >> troubleshooting automobile wiring/electronics I make the same
statement -
> >> "I
> >> hate working on car wiring". But... I do it, and I've been doing it a
> >> long
> >> time, so I understand this stuff pretty well, but I still hate it!
> >>
> >> --
> >>
> >> -Mike-
> >> mmarlowREMOVE@alltel.net
> >>
> >What concerns me is given that there's a delay before the fuse blows, and
> >wiring at 12 volts typically can't fail in a way that gives a high
> >resistance short that's hard enough that it blows a fuse. If it were a
high
> >resistance short, he'd be dissipating about 240 watts (~12 volts at ~20
amps
> >to blow a 10 amp fuse in a short but not instant time) at that high
> >resistance point - much smoke would be present. The other possibility is
a
> >motion induced hard short to ground. If he in fact has something that is
> >driven - a valve, etc - that has a short, and there's a delay before that
> >device is actuated, he runs the possibility of damaging the driver. I
mean,
> >how many times can an output take a short before failing. To try to
explain
> >to use a current limiting device in place of a fuse for troubleshooting -
a
> >lamp, etc.- and what the results should be is really difficult.
> >
>
> I disagree. If it's a 10A circuit the normal load would be
> ~12/10=1.2 ohm. It's going to look like a short to anything but a
> specialty resistance measuring circuit. I doubt it's really that low
> and it is not that low per sensor so measuring may locate the bad
> sensor. I would expect something like a 50% safety factor on the fuse
> so I'd expect an agregate load of ~2.4 ohms. Each individual load
> will be over that. Possibly well over that. If the circuit wiring is
> properly sized it will not smoke with that load. I have seen
> connectors with an ohm or more in a bad connection.
>
> Polarity probably will also be an issue. You are going to need to use
> the positive voltage resistance lead on the power lead to the sensor.
> If you are not sure what one that is use a second meter set to measure
> voltage and measure the voltage accross the probes of your resistance
> meter.
>
> Once You know the polarity probe the leads to the sensors with any
> ground lead connected to the chassis. I bet several will be over 100
> ohms so you can discount them for a first pass. If one is clearly
> below 2 or 3 ohms it is probably the problem. If all of them look OK
> then it is probably a function of the sensor activating and drawing
> too much current. The easiest way to find that will be to disconnect
> all of them then reconnect one at a time. You can either wait for the
> fuse to blow or connect an ammeter accross a blown fuse. Monitor the
> current draw as each sensor is connected. If I was doing this much
> that is what I would start with. ;-)
>
> If the fuse is blowing with the key on but not cranking the engine I
> bet you will find the answer fairly easily. You probaly have a blown
> semiconductor junction. It still has resistance, as does the
> packaging leads, but it's well below what it should be.
>
> nothermark

Ok, I unplugged all the sensors except the the canister close valve by the
fuel tank and canister purge valve under the throttle body. I turned on the
key and measured the current without the fuse in and it read 12.8
Then as soon as i put the fuse in it popped. I should mention the the car
was hit from behind recently enought to damage the rear bumper and
taillight.
Have to leave town tomorrow but will try some of the things suggested.

Thanks for all your help.

 

"nothermark" <trash@gnomex.cotse.net> wrote in message
news:vmnkv1l91d5i3snquafabfpojhvrga86g2@4ax.com...
> On Mon, 20 Feb 2006 18:13:22 -0500, "Bob" <bobsjunkmail@bellsouth.net>
> wrote:
>
> >
> >"Mike Marlow" <mmarlowREMOVE@alltel.net> wrote in message
> >news:dea96$43f9b46f$4528960b$13829@ALLTEL.NET.. .
> >>
> >> "Bob" <bobsjunkmail@bellsouth.net> wrote in message
> >> news:jaiKf.20641$bW.19251@bignews8.bellsouth.net.. .
> >>>
> >>> <sycore@bellsouth.net> wrote in message
> >>> news:kSbKf.20004$bW.11031@bignews8.bellsouth.net.. .
> >>> > it is the 2.7L v6 engine.
> >>> > I have a multimeter and can do the basics, but i am not the advanced
in
> >>> > testing.
> >>> > The fuse pops about 3-4 seconds after i turn the ignition key to on
> >>> > position.
> >>> > I can easily unplug all of the sesors except maybe the canister
close
> >>> > valve.
> >>> > Can i just plug them back in one at a time until it pops?
> >>>
> >>> 3-4 seconds means no "hard" short. You can try that, but without quite
a
> >> bit
> >>> of electrical troubleshooting experience, you can get in over your
head
> >>> pretty quickly.
> >>>
> >>>
> >>
> >> I don't know what the schematics show for this circuit Bob, but he'd
> >> likely
> >> be ok at least trying this approach - assuming that the circuit does
> >> really
> >> consist of the components the OP first indicated.
> >>
> >> You're right that 3-4 seconds implies a short with a resistance and not
a
> >> direct short., and that kind of troubleshooting with a meter can get
> >> confusing for folks who are not a little experienced. Depending upon
how
> >> the meter is set, it can potentially either look like a direct short
> >> (leading to replacing the wrong component in vain), or not even show
the
> >> short (leading to the obvious oversight).
> >>
> >> I think in this case - again, assuming the circuit is as described,
just
> >> go
> >> ahead as the OP suggests and disconnect the loads and selectively
> >> re-connect
> >> them. The caution with this technique is to make sure to inspect the
> >> wiring
> >> as well as the components.
> >>
> >> Over his head pretty quickly??? Hell - every time I get into
> >> troubleshooting automobile wiring/electronics I make the same
statement -
> >> "I
> >> hate working on car wiring". But... I do it, and I've been doing it a
> >> long
> >> time, so I understand this stuff pretty well, but I still hate it!
> >>
> >> --
> >>
> >> -Mike-
> >> mmarlowREMOVE@alltel.net
> >>
> >What concerns me is given that there's a delay before the fuse blows, and
> >wiring at 12 volts typically can't fail in a way that gives a high
> >resistance short that's hard enough that it blows a fuse. If it were a
high
> >resistance short, he'd be dissipating about 240 watts (~12 volts at ~20
amps
> >to blow a 10 amp fuse in a short but not instant time) at that high
> >resistance point - much smoke would be present. The other possibility is
a
> >motion induced hard short to ground. If he in fact has something that is
> >driven - a valve, etc - that has a short, and there's a delay before that
> >device is actuated, he runs the possibility of damaging the driver. I
mean,
> >how many times can an output take a short before failing. To try to
explain
> >to use a current limiting device in place of a fuse for troubleshooting -
a
> >lamp, etc.- and what the results should be is really difficult.
> >
>
> I disagree. If it's a 10A circuit the normal load would be
> ~12/10=1.2 ohm. It's going to look like a short to anything but a
> specialty resistance measuring circuit. I doubt it's really that low
> and it is not that low per sensor so measuring may locate the bad
> sensor. I would expect something like a 50% safety factor on the fuse
> so I'd expect an agregate load of ~2.4 ohms. Each individual load
> will be over that. Possibly well over that. If the circuit wiring is
> properly sized it will not smoke with that load. I have seen
> connectors with an ohm or more in a bad connection.
>
> Polarity probably will also be an issue. You are going to need to use
> the positive voltage resistance lead on the power lead to the sensor.
> If you are not sure what one that is use a second meter set to measure
> voltage and measure the voltage accross the probes of your resistance
> meter.
>
> Once You know the polarity probe the leads to the sensors with any
> ground lead connected to the chassis. I bet several will be over 100
> ohms so you can discount them for a first pass. If one is clearly
> below 2 or 3 ohms it is probably the problem. If all of them look OK
> then it is probably a function of the sensor activating and drawing
> too much current. The easiest way to find that will be to disconnect
> all of them then reconnect one at a time. You can either wait for the
> fuse to blow or connect an ammeter accross a blown fuse. Monitor the
> current draw as each sensor is connected. If I was doing this much
> that is what I would start with. ;-)
>
> If the fuse is blowing with the key on but not cranking the engine I
> bet you will find the answer fairly easily. You probaly have a blown
> semiconductor junction. It still has resistance, as does the
> packaging leads, but it's well below what it should be.
>
> nothermark

Ok, I unplugged all the sensors except the the canister close valve by the
fuel tank and canister purge valve under the throttle body. I turned on the
key and measured the current without the fuse in and it read 12.8
Then as soon as i put the fuse in it popped. I should mention the the car
was hit from behind recently enought to damage the rear bumper and
taillight.
Have to leave town tomorrow but will try some of the things suggested.

Thanks for all your help.

 

On Mon, 20 Feb 2006 23:23:01 -0600, <sycore@bellsouth.net> wrote:

>
>"nothermark" <trash@gnomex.cotse.net> wrote in message
>news:vmnkv1l91d5i3snquafabfpojhvrga86g2@4ax.com.. .
>> On Mon, 20 Feb 2006 18:13:22 -0500, "Bob" <bobsjunkmail@bellsouth.net>
>> wrote:
>>
>> >
>> >"Mike Marlow" <mmarlowREMOVE@alltel.net> wrote in message
>> >news:dea96$43f9b46f$4528960b$13829@ALLTEL.NET.. .
>> >>
>> >> "Bob" <bobsjunkmail@bellsouth.net> wrote in message
>> >> news:jaiKf.20641$bW.19251@bignews8.bellsouth.net.. .
>> >>>
>> >>> <sycore@bellsouth.net> wrote in message
>> >>> news:kSbKf.20004$bW.11031@bignews8.bellsouth.net.. .
>> >>> > it is the 2.7L v6 engine.
>> >>> > I have a multimeter and can do the basics, but i am not the advanced
>in
>> >>> > testing.
>> >>> > The fuse pops about 3-4 seconds after i turn the ignition key to on
>> >>> > position.
>> >>> > I can easily unplug all of the sesors except maybe the canister
>close
>> >>> > valve.
>> >>> > Can i just plug them back in one at a time until it pops?
>> >>>
>> >>> 3-4 seconds means no "hard" short. You can try that, but without quite
>a
>> >> bit
>> >>> of electrical troubleshooting experience, you can get in over your
>head
>> >>> pretty quickly.
>> >>>
>> >>>
>> >>
>> >> I don't know what the schematics show for this circuit Bob, but he'd
>> >> likely
>> >> be ok at least trying this approach - assuming that the circuit does
>> >> really
>> >> consist of the components the OP first indicated.
>> >>
>> >> You're right that 3-4 seconds implies a short with a resistance and not
>a
>> >> direct short., and that kind of troubleshooting with a meter can get
>> >> confusing for folks who are not a little experienced. Depending upon
>how
>> >> the meter is set, it can potentially either look like a direct short
>> >> (leading to replacing the wrong component in vain), or not even show
>the
>> >> short (leading to the obvious oversight).
>> >>
>> >> I think in this case - again, assuming the circuit is as described,
>just
>> >> go
>> >> ahead as the OP suggests and disconnect the loads and selectively
>> >> re-connect
>> >> them. The caution with this technique is to make sure to inspect the
>> >> wiring
>> >> as well as the components.
>> >>
>> >> Over his head pretty quickly??? Hell - every time I get into
>> >> troubleshooting automobile wiring/electronics I make the same
>statement -
>> >> "I
>> >> hate working on car wiring". But... I do it, and I've been doing it a
>> >> long
>> >> time, so I understand this stuff pretty well, but I still hate it!
>> >>
>> >> --
>> >>
>> >> -Mike-
>> >> mmarlowREMOVE@alltel.net
>> >>
>> >What concerns me is given that there's a delay before the fuse blows, and
>> >wiring at 12 volts typically can't fail in a way that gives a high
>> >resistance short that's hard enough that it blows a fuse. If it were a
>high
>> >resistance short, he'd be dissipating about 240 watts (~12 volts at ~20
>amps
>> >to blow a 10 amp fuse in a short but not instant time) at that high
>> >resistance point - much smoke would be present. The other possibility is
>a
>> >motion induced hard short to ground. If he in fact has something that is
>> >driven - a valve, etc - that has a short, and there's a delay before that
>> >device is actuated, he runs the possibility of damaging the driver. I
>mean,
>> >how many times can an output take a short before failing. To try to
>explain
>> >to use a current limiting device in place of a fuse for troubleshooting -
>a
>> >lamp, etc.- and what the results should be is really difficult.
>> >
>>
>> I disagree. If it's a 10A circuit the normal load would be
>> ~12/10=1.2 ohm. It's going to look like a short to anything but a
>> specialty resistance measuring circuit. I doubt it's really that low
>> and it is not that low per sensor so measuring may locate the bad
>> sensor. I would expect something like a 50% safety factor on the fuse
>> so I'd expect an agregate load of ~2.4 ohms. Each individual load
>> will be over that. Possibly well over that. If the circuit wiring is
>> properly sized it will not smoke with that load. I have seen
>> connectors with an ohm or more in a bad connection.
>>
>> Polarity probably will also be an issue. You are going to need to use
>> the positive voltage resistance lead on the power lead to the sensor.
>> If you are not sure what one that is use a second meter set to measure
>> voltage and measure the voltage accross the probes of your resistance
>> meter.
>>
>> Once You know the polarity probe the leads to the sensors with any
>> ground lead connected to the chassis. I bet several will be over 100
>> ohms so you can discount them for a first pass. If one is clearly
>> below 2 or 3 ohms it is probably the problem. If all of them look OK
>> then it is probably a function of the sensor activating and drawing
>> too much current. The easiest way to find that will be to disconnect
>> all of them then reconnect one at a time. You can either wait for the
>> fuse to blow or connect an ammeter accross a blown fuse. Monitor the
>> current draw as each sensor is connected. If I was doing this much
>> that is what I would start with. ;-)
>>
>> If the fuse is blowing with the key on but not cranking the engine I
>> bet you will find the answer fairly easily. You probaly have a blown
>> semiconductor junction. It still has resistance, as does the
>> packaging leads, but it's well below what it should be.
>>
>> nothermark
>
>Ok, I unplugged all the sensors except the the canister close valve by the
>fuel tank and canister purge valve under the throttle body. I turned on the
>key and measured the current without the fuse in and it read 12.8
>Then as soon as i put the fuse in it popped. I should mention the the car
>was hit from behind recently enought to damage the rear bumper and
>taillight.
>Have to leave town tomorrow but will try some of the things suggested.
>
>Thanks for all your help.
>

I am thinking pinched wire around the purge valve only because of the
accident. It looks like you have about 1 ohm so it could be a bad
connection limiting the current. If you are getting 12.8 A I would be
tempted to put in a 20 A fuse and see where things were gettting warm.
I'm not sure that is a good answer to do alone as I would be concerned
about burning something up. If you can have someone turn the key on
for 10 or 15 seconds while you hold the wires to the sensors in
question you may find one heating noticeably. Just watch for wires
getting hot enough to melt insulation.

The other thing that might happen is that you blow the sensor open and
stop drawing current. If it was a bad power transistor the initial
failure would be the reverse biased junction shorting so the total
wiring resistance becomes the current limit. The internal leads in
the package are usually the next thing to fuse but they usually blow
open. An open circuit should let the diagnostic routines find the bad
sensor.

 

On Mon, 20 Feb 2006 23:23:01 -0600, <sycore@bellsouth.net> wrote:

>
>"nothermark" <trash@gnomex.cotse.net> wrote in message
>news:vmnkv1l91d5i3snquafabfpojhvrga86g2@4ax.com.. .
>> On Mon, 20 Feb 2006 18:13:22 -0500, "Bob" <bobsjunkmail@bellsouth.net>
>> wrote:
>>
>> >
>> >"Mike Marlow" <mmarlowREMOVE@alltel.net> wrote in message
>> >news:dea96$43f9b46f$4528960b$13829@ALLTEL.NET.. .
>> >>
>> >> "Bob" <bobsjunkmail@bellsouth.net> wrote in message
>> >> news:jaiKf.20641$bW.19251@bignews8.bellsouth.net.. .
>> >>>
>> >>> <sycore@bellsouth.net> wrote in message
>> >>> news:kSbKf.20004$bW.11031@bignews8.bellsouth.net.. .
>> >>> > it is the 2.7L v6 engine.
>> >>> > I have a multimeter and can do the basics, but i am not the advanced
>in
>> >>> > testing.
>> >>> > The fuse pops about 3-4 seconds after i turn the ignition key to on
>> >>> > position.
>> >>> > I can easily unplug all of the sesors except maybe the canister
>close
>> >>> > valve.
>> >>> > Can i just plug them back in one at a time until it pops?
>> >>>
>> >>> 3-4 seconds means no "hard" short. You can try that, but without quite
>a
>> >> bit
>> >>> of electrical troubleshooting experience, you can get in over your
>head
>> >>> pretty quickly.
>> >>>
>> >>>
>> >>
>> >> I don't know what the schematics show for this circuit Bob, but he'd
>> >> likely
>> >> be ok at least trying this approach - assuming that the circuit does
>> >> really
>> >> consist of the components the OP first indicated.
>> >>
>> >> You're right that 3-4 seconds implies a short with a resistance and not
>a
>> >> direct short., and that kind of troubleshooting with a meter can get
>> >> confusing for folks who are not a little experienced. Depending upon
>how
>> >> the meter is set, it can potentially either look like a direct short
>> >> (leading to replacing the wrong component in vain), or not even show
>the
>> >> short (leading to the obvious oversight).
>> >>
>> >> I think in this case - again, assuming the circuit is as described,
>just
>> >> go
>> >> ahead as the OP suggests and disconnect the loads and selectively
>> >> re-connect
>> >> them. The caution with this technique is to make sure to inspect the
>> >> wiring
>> >> as well as the components.
>> >>
>> >> Over his head pretty quickly??? Hell - every time I get into
>> >> troubleshooting automobile wiring/electronics I make the same
>statement -
>> >> "I
>> >> hate working on car wiring". But... I do it, and I've been doing it a
>> >> long
>> >> time, so I understand this stuff pretty well, but I still hate it!
>> >>
>> >> --
>> >>
>> >> -Mike-
>> >> mmarlowREMOVE@alltel.net
>> >>
>> >What concerns me is given that there's a delay before the fuse blows, and
>> >wiring at 12 volts typically can't fail in a way that gives a high
>> >resistance short that's hard enough that it blows a fuse. If it were a
>high
>> >resistance short, he'd be dissipating about 240 watts (~12 volts at ~20
>amps
>> >to blow a 10 amp fuse in a short but not instant time) at that high
>> >resistance point - much smoke would be present. The other possibility is
>a
>> >motion induced hard short to ground. If he in fact has something that is
>> >driven - a valve, etc - that has a short, and there's a delay before that
>> >device is actuated, he runs the possibility of damaging the driver. I
>mean,
>> >how many times can an output take a short before failing. To try to
>explain
>> >to use a current limiting device in place of a fuse for troubleshooting -
>a
>> >lamp, etc.- and what the results should be is really difficult.
>> >
>>
>> I disagree. If it's a 10A circuit the normal load would be
>> ~12/10=1.2 ohm. It's going to look like a short to anything but a
>> specialty resistance measuring circuit. I doubt it's really that low
>> and it is not that low per sensor so measuring may locate the bad
>> sensor. I would expect something like a 50% safety factor on the fuse
>> so I'd expect an agregate load of ~2.4 ohms. Each individual load
>> will be over that. Possibly well over that. If the circuit wiring is
>> properly sized it will not smoke with that load. I have seen
>> connectors with an ohm or more in a bad connection.
>>
>> Polarity probably will also be an issue. You are going to need to use
>> the positive voltage resistance lead on the power lead to the sensor.
>> If you are not sure what one that is use a second meter set to measure
>> voltage and measure the voltage accross the probes of your resistance
>> meter.
>>
>> Once You know the polarity probe the leads to the sensors with any
>> ground lead connected to the chassis. I bet several will be over 100
>> ohms so you can discount them for a first pass. If one is clearly
>> below 2 or 3 ohms it is probably the problem. If all of them look OK
>> then it is probably a function of the sensor activating and drawing
>> too much current. The easiest way to find that will be to disconnect
>> all of them then reconnect one at a time. You can either wait for the
>> fuse to blow or connect an ammeter accross a blown fuse. Monitor the
>> current draw as each sensor is connected. If I was doing this much
>> that is what I would start with. ;-)
>>
>> If the fuse is blowing with the key on but not cranking the engine I
>> bet you will find the answer fairly easily. You probaly have a blown
>> semiconductor junction. It still has resistance, as does the
>> packaging leads, but it's well below what it should be.
>>
>> nothermark
>
>Ok, I unplugged all the sensors except the the canister close valve by the
>fuel tank and canister purge valve under the throttle body. I turned on the
>key and measured the current without the fuse in and it read 12.8
>Then as soon as i put the fuse in it popped. I should mention the the car
>was hit from behind recently enought to damage the rear bumper and
>taillight.
>Have to leave town tomorrow but will try some of the things suggested.
>
>Thanks for all your help.
>

I am thinking pinched wire around the purge valve only because of the
accident. It looks like you have about 1 ohm so it could be a bad
connection limiting the current. If you are getting 12.8 A I would be
tempted to put in a 20 A fuse and see where things were gettting warm.
I'm not sure that is a good answer to do alone as I would be concerned
about burning something up. If you can have someone turn the key on
for 10 or 15 seconds while you hold the wires to the sensors in
question you may find one heating noticeably. Just watch for wires
getting hot enough to melt insulation.

The other thing that might happen is that you blow the sensor open and
stop drawing current. If it was a bad power transistor the initial
failure would be the reverse biased junction shorting so the total
wiring resistance becomes the current limit. The internal leads in
the package are usually the next thing to fuse but they usually blow
open. An open circuit should let the diagnostic routines find the bad
sensor.

 

On Mon, 20 Feb 2006 23:23:01 -0600, <sycore@bellsouth.net> wrote:

>
>"nothermark" <trash@gnomex.cotse.net> wrote in message
>news:vmnkv1l91d5i3snquafabfpojhvrga86g2@4ax.com.. .
>> On Mon, 20 Feb 2006 18:13:22 -0500, "Bob" <bobsjunkmail@bellsouth.net>
>> wrote:
>>
>> >
>> >"Mike Marlow" <mmarlowREMOVE@alltel.net> wrote in message
>> >news:dea96$43f9b46f$4528960b$13829@ALLTEL.NET.. .
>> >>
>> >> "Bob" <bobsjunkmail@bellsouth.net> wrote in message
>> >> news:jaiKf.20641$bW.19251@bignews8.bellsouth.net.. .
>> >>>
>> >>> <sycore@bellsouth.net> wrote in message
>> >>> news:kSbKf.20004$bW.11031@bignews8.bellsouth.net.. .
>> >>> > it is the 2.7L v6 engine.
>> >>> > I have a multimeter and can do the basics, but i am not the advanced
>in
>> >>> > testing.
>> >>> > The fuse pops about 3-4 seconds after i turn the ignition key to on
>> >>> > position.
>> >>> > I can easily unplug all of the sesors except maybe the canister
>close
>> >>> > valve.
>> >>> > Can i just plug them back in one at a time until it pops?
>> >>>
>> >>> 3-4 seconds means no "hard" short. You can try that, but without quite
>a
>> >> bit
>> >>> of electrical troubleshooting experience, you can get in over your
>head
>> >>> pretty quickly.
>> >>>
>> >>>
>> >>
>> >> I don't know what the schematics show for this circuit Bob, but he'd
>> >> likely
>> >> be ok at least trying this approach - assuming that the circuit does
>> >> really
>> >> consist of the components the OP first indicated.
>> >>
>> >> You're right that 3-4 seconds implies a short with a resistance and not
>a
>> >> direct short., and that kind of troubleshooting with a meter can get
>> >> confusing for folks who are not a little experienced. Depending upon
>how
>> >> the meter is set, it can potentially either look like a direct short
>> >> (leading to replacing the wrong component in vain), or not even show
>the
>> >> short (leading to the obvious oversight).
>> >>
>> >> I think in this case - again, assuming the circuit is as described,
>just
>> >> go
>> >> ahead as the OP suggests and disconnect the loads and selectively
>> >> re-connect
>> >> them. The caution with this technique is to make sure to inspect the
>> >> wiring
>> >> as well as the components.
>> >>
>> >> Over his head pretty quickly??? Hell - every time I get into
>> >> troubleshooting automobile wiring/electronics I make the same
>statement -
>> >> "I
>> >> hate working on car wiring". But... I do it, and I've been doing it a
>> >> long
>> >> time, so I understand this stuff pretty well, but I still hate it!
>> >>
>> >> --
>> >>
>> >> -Mike-
>> >> mmarlowREMOVE@alltel.net
>> >>
>> >What concerns me is given that there's a delay before the fuse blows, and
>> >wiring at 12 volts typically can't fail in a way that gives a high
>> >resistance short that's hard enough that it blows a fuse. If it were a
>high
>> >resistance short, he'd be dissipating about 240 watts (~12 volts at ~20
>amps
>> >to blow a 10 amp fuse in a short but not instant time) at that high
>> >resistance point - much smoke would be present. The other possibility is
>a
>> >motion induced hard short to ground. If he in fact has something that is
>> >driven - a valve, etc - that has a short, and there's a delay before that
>> >device is actuated, he runs the possibility of damaging the driver. I
>mean,
>> >how many times can an output take a short before failing. To try to
>explain
>> >to use a current limiting device in place of a fuse for troubleshooting -
>a
>> >lamp, etc.- and what the results should be is really difficult.
>> >
>>
>> I disagree. If it's a 10A circuit the normal load would be
>> ~12/10=1.2 ohm. It's going to look like a short to anything but a
>> specialty resistance measuring circuit. I doubt it's really that low
>> and it is not that low per sensor so measuring may locate the bad
>> sensor. I would expect something like a 50% safety factor on the fuse
>> so I'd expect an agregate load of ~2.4 ohms. Each individual load
>> will be over that. Possibly well over that. If the circuit wiring is
>> properly sized it will not smoke with that load. I have seen
>> connectors with an ohm or more in a bad connection.
>>
>> Polarity probably will also be an issue. You are going to need to use
>> the positive voltage resistance lead on the power lead to the sensor.
>> If you are not sure what one that is use a second meter set to measure
>> voltage and measure the voltage accross the probes of your resistance
>> meter.
>>
>> Once You know the polarity probe the leads to the sensors with any
>> ground lead connected to the chassis. I bet several will be over 100
>> ohms so you can discount them for a first pass. If one is clearly
>> below 2 or 3 ohms it is probably the problem. If all of them look OK
>> then it is probably a function of the sensor activating and drawing
>> too much current. The easiest way to find that will be to disconnect
>> all of them then reconnect one at a time. You can either wait for the
>> fuse to blow or connect an ammeter accross a blown fuse. Monitor the
>> current draw as each sensor is connected. If I was doing this much
>> that is what I would start with. ;-)
>>
>> If the fuse is blowing with the key on but not cranking the engine I
>> bet you will find the answer fairly easily. You probaly have a blown
>> semiconductor junction. It still has resistance, as does the
>> packaging leads, but it's well below what it should be.
>>
>> nothermark
>
>Ok, I unplugged all the sensors except the the canister close valve by the
>fuel tank and canister purge valve under the throttle body. I turned on the
>key and measured the current without the fuse in and it read 12.8
>Then as soon as i put the fuse in it popped. I should mention the the car
>was hit from behind recently enought to damage the rear bumper and
>taillight.
>Have to leave town tomorrow but will try some of the things suggested.
>
>Thanks for all your help.
>

I am thinking pinched wire around the purge valve only because of the
accident. It looks like you have about 1 ohm so it could be a bad
connection limiting the current. If you are getting 12.8 A I would be
tempted to put in a 20 A fuse and see where things were gettting warm.
I'm not sure that is a good answer to do alone as I would be concerned
about burning something up. If you can have someone turn the key on
for 10 or 15 seconds while you hold the wires to the sensors in
question you may find one heating noticeably. Just watch for wires
getting hot enough to melt insulation.

The other thing that might happen is that you blow the sensor open and
stop drawing current. If it was a bad power transistor the initial
failure would be the reverse biased junction shorting so the total
wiring resistance becomes the current limit. The internal leads in
the package are usually the next thing to fuse but they usually blow
open. An open circuit should let the diagnostic routines find the bad
sensor.

 

took this out of the other thread because it's less relevant to his
problem.

On Mon, 20 Feb 2006 21:46:19 -0500, "Bob" <bobsjunkmail@bellsouth.net>
wrote:

>
>"nothermark" <trash@gnomex.cotse.net> wrote in message
>news:vmnkv1l91d5i3snquafabfpojhvrga86g2@4ax.com.. .
>
>> I disagree. If it's a 10A circuit the normal load would be
>> ~12/10=1.2 ohm. It's going to look like a short to anything but a
>> specialty resistance measuring circuit. I doubt it's really that low
>> and it is not that low per sensor so measuring may locate the bad
>> sensor. I would expect something like a 50% safety factor on the fuse
>> so I'd expect an agregate load of ~2.4 ohms. Each individual load
>> will be over that. Possibly well over that. If the circuit wiring is
>> properly sized it will not smoke with that load. I have seen
>> connectors with an ohm or more in a bad connection.
>I'm not talking about burning the wire. A properly sized fuse will open
>prior to the wiring heating significantly. What I am concerned with - if it
>is a wiring issue - is that the point where the wire is being grounded, and
>whatever the path to ground is is dropping the entire battery voltage over
>what is likely a small area. According to the fusing tables, you need 15
>amps of current to blow a 10 amp fuse in 4 seconds. So, the entire
>dissipation over the wire and the short to ground is 12v * 15a = 180 watts.
>15 amps would be a total resistance to ground of .8 ohms. If he looks at O2
>sensors, they start out as fairly low resistance, so that may be a little
>misleading.

I think he indicated the problem circuit does not include the O2
sensor. I'm not too worried about the power draw as long as he does
not jumper the fuse with a large wire. As you pointed out, and he
measured, the current is limited to around 12 - 15 A so On times of 10
seconds or so won't do more than run down the battery or blow the bad
sensor open. Even melting something is not all bad as it points out
the problem. The only thing I would feel bad about there is one wire
in a large bundle and it took out the bundle.

>
>>
>> Polarity probably will also be an issue. You are going to need to use
>> the positive voltage resistance lead on the power lead to the sensor.
>> If you are not sure what one that is use a second meter set to measure
>> voltage and measure the voltage accross the probes of your resistance
>> meter.
>
>If he's got a digital meter, most of them will not forward bias any diodes
>present in things like position sensors, so he won't even see them. They are
>not likely culprits anyway.

I was thinking more about a reverse polarity diode accross the sensor.
I've seen them on a lot of automotive comm gear as the power from the
alternator is pretty dirty. Most meters will detect that. That's how
we check transistors. ;-)


>
>> Once You know the polarity probe the leads to the sensors with any
>> ground lead connected to the chassis. I bet several will be over 100
>> ohms so you can discount them for a first pass. If one is clearly
>> below 2 or 3 ohms it is probably the problem. If all of them look OK
>> then it is probably a function of the sensor activating and drawing
>> too much current. The easiest way to find that will be to disconnect
>> all of them then reconnect one at a time. You can either wait for the
>> fuse to blow or connect an ammeter across a blown fuse. Monitor the
>> current draw as each sensor is connected. If I was doing this much
>> that is what I would start with. ;-)
>
>If he puts an ammeter (like the one in his meter) across the open fuse,
>he'll either cook his meter, or blow the current fuse in it (if there is
>one).

Not really. It's already taking several seconds to blow the fuse so
we know the current is limited. A 20 or 50 A current meter like he
needs is pretty rugged. What I think I advised is that he pull all
the sensor wires and put them back as he watched the meter. I assumed
he would turn off the power or pull off the lead if he pegged the
meter. Perhaps I assume too much?




>Something that works well - if you don't have access to a current limited
>power supply - is to use a high current lamp - like one or both filaments in
>a 60 watt headlamp - in place of the fuse. Low current flow = no heating of
>filament, so little drop across it. Short to ground = light lights, and
>current is limited to about 5 amps for one filament, or about 10 amps for 2
>in parallel. In either case, you can start disconnecting (or connecting)
>things and watch continuously for what changes.

Your way is more elegant, just takes more fussing around. If I was
doing much trouble shooting I would probably build a lamp bank. I was
giving him a one shot quicky approach.


>
>
>> If the fuse is blowing with the key on but not cranking the engine I
>> bet you will find the answer fairly easily. You probaly have a blown
>> semiconductor junction. It still has resistance, as does the
>> packaging leads, but it's well below what it should be.
>>
>> nothermark
>

 

took this out of the other thread because it's less relevant to his
problem.

On Mon, 20 Feb 2006 21:46:19 -0500, "Bob" <bobsjunkmail@bellsouth.net>
wrote:

>
>"nothermark" <trash@gnomex.cotse.net> wrote in message
>news:vmnkv1l91d5i3snquafabfpojhvrga86g2@4ax.com.. .
>
>> I disagree. If it's a 10A circuit the normal load would be
>> ~12/10=1.2 ohm. It's going to look like a short to anything but a
>> specialty resistance measuring circuit. I doubt it's really that low
>> and it is not that low per sensor so measuring may locate the bad
>> sensor. I would expect something like a 50% safety factor on the fuse
>> so I'd expect an agregate load of ~2.4 ohms. Each individual load
>> will be over that. Possibly well over that. If the circuit wiring is
>> properly sized it will not smoke with that load. I have seen
>> connectors with an ohm or more in a bad connection.
>I'm not talking about burning the wire. A properly sized fuse will open
>prior to the wiring heating significantly. What I am concerned with - if it
>is a wiring issue - is that the point where the wire is being grounded, and
>whatever the path to ground is is dropping the entire battery voltage over
>what is likely a small area. According to the fusing tables, you need 15
>amps of current to blow a 10 amp fuse in 4 seconds. So, the entire
>dissipation over the wire and the short to ground is 12v * 15a = 180 watts.
>15 amps would be a total resistance to ground of .8 ohms. If he looks at O2
>sensors, they start out as fairly low resistance, so that may be a little
>misleading.

I think he indicated the problem circuit does not include the O2
sensor. I'm not too worried about the power draw as long as he does
not jumper the fuse with a large wire. As you pointed out, and he
measured, the current is limited to around 12 - 15 A so On times of 10
seconds or so won't do more than run down the battery or blow the bad
sensor open. Even melting something is not all bad as it points out
the problem. The only thing I would feel bad about there is one wire
in a large bundle and it took out the bundle.

>
>>
>> Polarity probably will also be an issue. You are going to need to use
>> the positive voltage resistance lead on the power lead to the sensor.
>> If you are not sure what one that is use a second meter set to measure
>> voltage and measure the voltage accross the probes of your resistance
>> meter.
>
>If he's got a digital meter, most of them will not forward bias any diodes
>present in things like position sensors, so he won't even see them. They are
>not likely culprits anyway.

I was thinking more about a reverse polarity diode accross the sensor.
I've seen them on a lot of automotive comm gear as the power from the
alternator is pretty dirty. Most meters will detect that. That's how
we check transistors. ;-)


>
>> Once You know the polarity probe the leads to the sensors with any
>> ground lead connected to the chassis. I bet several will be over 100
>> ohms so you can discount them for a first pass. If one is clearly
>> below 2 or 3 ohms it is probably the problem. If all of them look OK
>> then it is probably a function of the sensor activating and drawing
>> too much current. The easiest way to find that will be to disconnect
>> all of them then reconnect one at a time. You can either wait for the
>> fuse to blow or connect an ammeter across a blown fuse. Monitor the
>> current draw as each sensor is connected. If I was doing this much
>> that is what I would start with. ;-)
>
>If he puts an ammeter (like the one in his meter) across the open fuse,
>he'll either cook his meter, or blow the current fuse in it (if there is
>one).

Not really. It's already taking several seconds to blow the fuse so
we know the current is limited. A 20 or 50 A current meter like he
needs is pretty rugged. What I think I advised is that he pull all
the sensor wires and put them back as he watched the meter. I assumed
he would turn off the power or pull off the lead if he pegged the
meter. Perhaps I assume too much?




>Something that works well - if you don't have access to a current limited
>power supply - is to use a high current lamp - like one or both filaments in
>a 60 watt headlamp - in place of the fuse. Low current flow = no heating of
>filament, so little drop across it. Short to ground = light lights, and
>current is limited to about 5 amps for one filament, or about 10 amps for 2
>in parallel. In either case, you can start disconnecting (or connecting)
>things and watch continuously for what changes.

Your way is more elegant, just takes more fussing around. If I was
doing much trouble shooting I would probably build a lamp bank. I was
giving him a one shot quicky approach.


>
>
>> If the fuse is blowing with the key on but not cranking the engine I
>> bet you will find the answer fairly easily. You probaly have a blown
>> semiconductor junction. It still has resistance, as does the
>> packaging leads, but it's well below what it should be.
>>
>> nothermark
>

 

took this out of the other thread because it's less relevant to his
problem.

On Mon, 20 Feb 2006 21:46:19 -0500, "Bob" <bobsjunkmail@bellsouth.net>
wrote:

>
>"nothermark" <trash@gnomex.cotse.net> wrote in message
>news:vmnkv1l91d5i3snquafabfpojhvrga86g2@4ax.com.. .
>
>> I disagree. If it's a 10A circuit the normal load would be
>> ~12/10=1.2 ohm. It's going to look like a short to anything but a
>> specialty resistance measuring circuit. I doubt it's really that low
>> and it is not that low per sensor so measuring may locate the bad
>> sensor. I would expect something like a 50% safety factor on the fuse
>> so I'd expect an agregate load of ~2.4 ohms. Each individual load
>> will be over that. Possibly well over that. If the circuit wiring is
>> properly sized it will not smoke with that load. I have seen
>> connectors with an ohm or more in a bad connection.
>I'm not talking about burning the wire. A properly sized fuse will open
>prior to the wiring heating significantly. What I am concerned with - if it
>is a wiring issue - is that the point where the wire is being grounded, and
>whatever the path to ground is is dropping the entire battery voltage over
>what is likely a small area. According to the fusing tables, you need 15
>amps of current to blow a 10 amp fuse in 4 seconds. So, the entire
>dissipation over the wire and the short to ground is 12v * 15a = 180 watts.
>15 amps would be a total resistance to ground of .8 ohms. If he looks at O2
>sensors, they start out as fairly low resistance, so that may be a little
>misleading.

I think he indicated the problem circuit does not include the O2
sensor. I'm not too worried about the power draw as long as he does
not jumper the fuse with a large wire. As you pointed out, and he
measured, the current is limited to around 12 - 15 A so On times of 10
seconds or so won't do more than run down the battery or blow the bad
sensor open. Even melting something is not all bad as it points out
the problem. The only thing I would feel bad about there is one wire
in a large bundle and it took out the bundle.

>
>>
>> Polarity probably will also be an issue. You are going to need to use
>> the positive voltage resistance lead on the power lead to the sensor.
>> If you are not sure what one that is use a second meter set to measure
>> voltage and measure the voltage accross the probes of your resistance
>> meter.
>
>If he's got a digital meter, most of them will not forward bias any diodes
>present in things like position sensors, so he won't even see them. They are
>not likely culprits anyway.

I was thinking more about a reverse polarity diode accross the sensor.
I've seen them on a lot of automotive comm gear as the power from the
alternator is pretty dirty. Most meters will detect that. That's how
we check transistors. ;-)


>
>> Once You know the polarity probe the leads to the sensors with any
>> ground lead connected to the chassis. I bet several will be over 100
>> ohms so you can discount them for a first pass. If one is clearly
>> below 2 or 3 ohms it is probably the problem. If all of them look OK
>> then it is probably a function of the sensor activating and drawing
>> too much current. The easiest way to find that will be to disconnect
>> all of them then reconnect one at a time. You can either wait for the
>> fuse to blow or connect an ammeter across a blown fuse. Monitor the
>> current draw as each sensor is connected. If I was doing this much
>> that is what I would start with. ;-)
>
>If he puts an ammeter (like the one in his meter) across the open fuse,
>he'll either cook his meter, or blow the current fuse in it (if there is
>one).

Not really. It's already taking several seconds to blow the fuse so
we know the current is limited. A 20 or 50 A current meter like he
needs is pretty rugged. What I think I advised is that he pull all
the sensor wires and put them back as he watched the meter. I assumed
he would turn off the power or pull off the lead if he pegged the
meter. Perhaps I assume too much?




>Something that works well - if you don't have access to a current limited
>power supply - is to use a high current lamp - like one or both filaments in
>a 60 watt headlamp - in place of the fuse. Low current flow = no heating of
>filament, so little drop across it. Short to ground = light lights, and
>current is limited to about 5 amps for one filament, or about 10 amps for 2
>in parallel. In either case, you can start disconnecting (or connecting)
>things and watch continuously for what changes.

Your way is more elegant, just takes more fussing around. If I was
doing much trouble shooting I would probably build a lamp bank. I was
giving him a one shot quicky approach.


>
>
>> If the fuse is blowing with the key on but not cranking the engine I
>> bet you will find the answer fairly easily. You probaly have a blown
>> semiconductor junction. It still has resistance, as does the
>> packaging leads, but it's well below what it should be.
>>
>> nothermark
>

 

"nothermark" <trash@gnomex.cotse.net> wrote in message
news:4uhnv1hj2970evtgkp79i5lsv5u98v58fr@4ax.com...
> took this out of the other thread because it's less relevant to his
> problem.
>
> On Mon, 20 Feb 2006 21:46:19 -0500, "Bob" <bobsjunkmail@bellsouth.net>
> wrote:
>
>
> I think he indicated the problem circuit does not include the O2
> sensor. I'm not too worried about the power draw as long as he does
> not jumper the fuse with a large wire. As you pointed out, and he
> measured, the current is limited to around 12 - 15 A so On times of 10
> seconds or so won't do more than run down the battery or blow the bad
> sensor open. Even melting something is not all bad as it points out
> the problem. The only thing I would feel bad about there is one wire
> in a large bundle and it took out the bundle.

Which is my concern. At 15 amps, something is getting hot. I would prefer
not to torch something in the harness.

>>
>>>
>>> Polarity probably will also be an issue. You are going to need to use
>>> the positive voltage resistance lead on the power lead to the sensor.
>>> If you are not sure what one that is use a second meter set to measure
>>> voltage and measure the voltage accross the probes of your resistance
>>> meter.
>>
>>If he's got a digital meter, most of them will not forward bias any diodes
>>present in things like position sensors, so he won't even see them. They
>>are
>>not likely culprits anyway.
>
> I was thinking more about a reverse polarity diode accross the sensor.
> I've seen them on a lot of automotive comm gear as the power from the
> alternator is pretty dirty. Most meters will detect that. That's how
> we check transistors. ;-)
>
It really depends on the meter. I typically use Fluke 73s. In ohms mode,
they don't "see" diodes real well. That is done intentionally. They do have
a mode for looking at semiconductor junctions.

>
>>
>>> Once You know the polarity probe the leads to the sensors with any
>>> ground lead connected to the chassis. I bet several will be over 100
>>> ohms so you can discount them for a first pass. If one is clearly
>>> below 2 or 3 ohms it is probably the problem. If all of them look OK
>>> then it is probably a function of the sensor activating and drawing
>>> too much current. The easiest way to find that will be to disconnect
>>> all of them then reconnect one at a time. You can either wait for the
>>> fuse to blow or connect an ammeter across a blown fuse. Monitor the
>>> current draw as each sensor is connected. If I was doing this much
>>> that is what I would start with. ;-)
>>
>>If he puts an ammeter (like the one in his meter) across the open fuse,
>>he'll either cook his meter, or blow the current fuse in it (if there is
>>one).
>
> Not really. It's already taking several seconds to blow the fuse so
> we know the current is limited. A 20 or 50 A current meter like he
> needs is pretty rugged. What I think I advised is that he pull all
> the sensor wires and put them back as he watched the meter. I assumed
> he would turn off the power or pull off the lead if he pegged the
> meter. Perhaps I assume too much?
>
We really don't know what kind of meter he has. The less expensive meters
have a fuse on the low current path, and nothing but a current shunt on the
high current path. Cat. III / IV meters like the ones I use are actually
fused at relatively low values - 440 ma, and 11 amps for the high current
port. For high current DC I use either an external shunt, or a DC clamp on.
For AC, I normally use a clamp on. The DC systems I work on can have
available source currents as high as 40,000 amps at voltages from 12 on up
to 480 volts. I also work on switching equipment and control systems for
voltages as high as 230,000 volts at lots of current.
So, maybe you can understand why I'm not real big on the keep feeding it
fuses technique.

In automotive, it might work without major issues, but it may also
eventually damage something besides what is already broken. feeding a line
with a current limited source - either a fancy power supply, or a lamp as a
ballast resistor - is a pretty effective technique. When you've isolated it
to one line, and it's a wiring issue, you can feed that line from either
end, and determine which end the fault to ground is closer to, and maybe
even estimate relative distance. I work on a wide variety of DC powered
devices that communicate with serial data, tones, voltages, and currents.
The things I recommended against are just things I cannot do because I have
to be very careful not to cause additional damage, as repeatedly re-fusing a
known failed circuit - even in a car - can do.



>
>>Something that works well - if you don't have access to a current limited
>>power supply - is to use a high current lamp - like one or both filaments
>>in
>>a 60 watt headlamp - in place of the fuse. Low current flow = no heating
>>of
>>filament, so little drop across it. Short to ground = light lights, and
>>current is limited to about 5 amps for one filament, or about 10 amps for
>>2
>>in parallel. In either case, you can start disconnecting (or connecting)
>>things and watch continuously for what changes.
>
> Your way is more elegant, just takes more fussing around. If I was
> doing much trouble shooting I would probably build a lamp bank. I was
> giving him a one shot quicky approach.
>
>
I'm disputing that your suggestion will work. It just makes me cringe when
you suggested shorting across a blown fuse with an ammeter when we are not
sure whether that is fused, or will just melt. Also, the assumption that
he'll get his meter off it fast enough is another variable.
>>
>>
>>> If the fuse is blowing with the key on but not cranking the engine I
>>> bet you will find the answer fairly easily. You probaly have a blown
>>> semiconductor junction. It still has resistance, as does the
>>> packaging leads, but it's well below what it should be.
>>>
>>> nothermark
>>

 

"nothermark" <trash@gnomex.cotse.net> wrote in message
news:4uhnv1hj2970evtgkp79i5lsv5u98v58fr@4ax.com...
> took this out of the other thread because it's less relevant to his
> problem.
>
> On Mon, 20 Feb 2006 21:46:19 -0500, "Bob" <bobsjunkmail@bellsouth.net>
> wrote:
>
>
> I think he indicated the problem circuit does not include the O2
> sensor. I'm not too worried about the power draw as long as he does
> not jumper the fuse with a large wire. As you pointed out, and he
> measured, the current is limited to around 12 - 15 A so On times of 10
> seconds or so won't do more than run down the battery or blow the bad
> sensor open. Even melting something is not all bad as it points out
> the problem. The only thing I would feel bad about there is one wire
> in a large bundle and it took out the bundle.

Which is my concern. At 15 amps, something is getting hot. I would prefer
not to torch something in the harness.

>>
>>>
>>> Polarity probably will also be an issue. You are going to need to use
>>> the positive voltage resistance lead on the power lead to the sensor.
>>> If you are not sure what one that is use a second meter set to measure
>>> voltage and measure the voltage accross the probes of your resistance
>>> meter.
>>
>>If he's got a digital meter, most of them will not forward bias any diodes
>>present in things like position sensors, so he won't even see them. They
>>are
>>not likely culprits anyway.
>
> I was thinking more about a reverse polarity diode accross the sensor.
> I've seen them on a lot of automotive comm gear as the power from the
> alternator is pretty dirty. Most meters will detect that. That's how
> we check transistors. ;-)
>
It really depends on the meter. I typically use Fluke 73s. In ohms mode,
they don't "see" diodes real well. That is done intentionally. They do have
a mode for looking at semiconductor junctions.

>
>>
>>> Once You know the polarity probe the leads to the sensors with any
>>> ground lead connected to the chassis. I bet several will be over 100
>>> ohms so you can discount them for a first pass. If one is clearly
>>> below 2 or 3 ohms it is probably the problem. If all of them look OK
>>> then it is probably a function of the sensor activating and drawing
>>> too much current. The easiest way to find that will be to disconnect
>>> all of them then reconnect one at a time. You can either wait for the
>>> fuse to blow or connect an ammeter across a blown fuse. Monitor the
>>> current draw as each sensor is connected. If I was doing this much
>>> that is what I would start with. ;-)
>>
>>If he puts an ammeter (like the one in his meter) across the open fuse,
>>he'll either cook his meter, or blow the current fuse in it (if there is
>>one).
>
> Not really. It's already taking several seconds to blow the fuse so
> we know the current is limited. A 20 or 50 A current meter like he
> needs is pretty rugged. What I think I advised is that he pull all
> the sensor wires and put them back as he watched the meter. I assumed
> he would turn off the power or pull off the lead if he pegged the
> meter. Perhaps I assume too much?
>
We really don't know what kind of meter he has. The less expensive meters
have a fuse on the low current path, and nothing but a current shunt on the
high current path. Cat. III / IV meters like the ones I use are actually
fused at relatively low values - 440 ma, and 11 amps for the high current
port. For high current DC I use either an external shunt, or a DC clamp on.
For AC, I normally use a clamp on. The DC systems I work on can have
available source currents as high as 40,000 amps at voltages from 12 on up
to 480 volts. I also work on switching equipment and control systems for
voltages as high as 230,000 volts at lots of current.
So, maybe you can understand why I'm not real big on the keep feeding it
fuses technique.

In automotive, it might work without major issues, but it may also
eventually damage something besides what is already broken. feeding a line
with a current limited source - either a fancy power supply, or a lamp as a
ballast resistor - is a pretty effective technique. When you've isolated it
to one line, and it's a wiring issue, you can feed that line from either
end, and determine which end the fault to ground is closer to, and maybe
even estimate relative distance. I work on a wide variety of DC powered
devices that communicate with serial data, tones, voltages, and currents.
The things I recommended against are just things I cannot do because I have
to be very careful not to cause additional damage, as repeatedly re-fusing a
known failed circuit - even in a car - can do.



>
>>Something that works well - if you don't have access to a current limited
>>power supply - is to use a high current lamp - like one or both filaments
>>in
>>a 60 watt headlamp - in place of the fuse. Low current flow = no heating
>>of
>>filament, so little drop across it. Short to ground = light lights, and
>>current is limited to about 5 amps for one filament, or about 10 amps for
>>2
>>in parallel. In either case, you can start disconnecting (or connecting)
>>things and watch continuously for what changes.
>
> Your way is more elegant, just takes more fussing around. If I was
> doing much trouble shooting I would probably build a lamp bank. I was
> giving him a one shot quicky approach.
>
>
I'm disputing that your suggestion will work. It just makes me cringe when
you suggested shorting across a blown fuse with an ammeter when we are not
sure whether that is fused, or will just melt. Also, the assumption that
he'll get his meter off it fast enough is another variable.
>>
>>
>>> If the fuse is blowing with the key on but not cranking the engine I
>>> bet you will find the answer fairly easily. You probaly have a blown
>>> semiconductor junction. It still has resistance, as does the
>>> packaging leads, but it's well below what it should be.
>>>
>>> nothermark
>>