Re: 93 Honda Civic Mileage gone bad
 

Manual tranny. VTEC is *not* electronic, it is controlled PER cylinder
by oil pressure. RPMs go up = more pressure. at a certain point, the
pins slide in and the intake valves use a different cam lobe. I
checked when I adjusted the valves, they weren't stuck. But I doubt one
VTEC being stuck on one cylinder would change the mileage this much.


Driving habits have not changed.

Nope, Oil is 10w30, hasn't changed.

I have the Factory Service Manual, it's pretty useful.

Re: 93 Honda Civic Mileage gone bad
 

Sounds resonable, but then the Check engine light would be lit if the
sensor were failing... Well, "should" be it.

Re: 93 Honda Civic Mileage gone bad
 

The old plugs were perfect and all the same.

Tires are properly inflated, brakes are not dragging. I also just
replaced the front rotors and pads.

Re: 93 Honda Civic Mileage gone bad
 

Danny Beardsley wrote:
> Sounds resonable, but then the Check engine light would be lit if the
> sensor were failing... Well, "should" be it.
>
i dont think itll light up the check engine lamp on a pre-96/OBD2 car.
might not even throw a code. but the O2 sensor definately has an effect
on the mileage, and by 200k miles with the original sensor, its time to
replace.

Re: 93 Honda Civic Mileage gone bad
 

| Consider a new oxygen sensor.
Without checking its output 1st ? This is stupid, user can chk sensor's
output easily. http://home.flash.net/~lorint/lorin/fuel/lambda.htm
If voltage is unstable, injectors are likely clogged.

| > any ideas about the milage?
chk car's minimum toe force needed ; tyres' toe-in may have increased
with usage, present tyres may have higher rolling resistance

Re: 93 Honda Civic Mileage gone bad
 

"Danny Beardsley" <dbeardsl@gmail.com> wrote in message
news:1134205847.172890.185610@g14g2000cwa.googlegr oups.com...
> The old plugs were perfect and all the same.
>
> Tires are properly inflated, brakes are not dragging. I also just
> replaced the front rotors and pads.
>
Did you readjust the parking brake? In one of the Prius groups a member was
complaining the mileage dropped about 10-20% after the most recent service,
and another suggested the parking brake had been adjusted too tight. Bingo!
(I am also assuming the slide pins were lubed during the brake work. Once I
overlooked that bit and received one of life's little lessons.) If you have
verified the brakes are not dragging, the parking brake isn't it... but the
lubrication state still could be.

Mike

Re: 93 Honda Civic Mileage gone bad
 

Danny Beardsley wrote:
> Manual tranny. VTEC is *not* electronic, it is controlled PER cylinder
> by oil pressure. RPMs go up = more pressure. at a certain point, the
> pins slide in and the intake valves use a different cam lobe.

the vtec /is/ applied by oil pressure, but the oil is "switched" on and
off from the oil channel by an electrical solenoid. that is in turn
controlled by the ecu. simple oil pressure control is subject to too
many variables to be reliable.

> I
> checked when I adjusted the valves, they weren't stuck. But I doubt one
> VTEC being stuck on one cylinder would change the mileage this much.
>
>
> Driving habits have not changed.
>
> Nope, Oil is 10w30, hasn't changed.
>
> I have the Factory Service Manual, it's pretty useful.
>

non-activating vtec is /most/ unlikely to be the cause of declining gas
mileage.

Re: 93 Honda Civic Mileage gone bad
 

Michael Pardee wrote:
> "Danny Beardsley" <dbeardsl@gmail.com> wrote in message
> news:1134205847.172890.185610@g14g2000cwa.googlegr oups.com...
>
>>The old plugs were perfect and all the same.
>>
>>Tires are properly inflated, brakes are not dragging. I also just
>>replaced the front rotors and pads.
>>
>
> Did you readjust the parking brake? In one of the Prius groups a member was
> complaining the mileage dropped about 10-20% after the most recent service,
> and another suggested the parking brake had been adjusted too tight. Bingo!
> (I am also assuming the slide pins were lubed during the brake work. Once I
> overlooked that bit and received one of life's little lessons.) If you have
> verified the brakes are not dragging, the parking brake isn't it... but the
> lubrication state still could be.
>
> Mike
>
>
parking brake is self adjusting. should not be affected by servicing
the front! but it's a good thought - check the brakes - especially as
decreased gas mileage seems to coincide with recent brake service!!!

Re: 93 Honda Civic Mileage gone bad
 

"Danny Beardsley" <dbeardsl@gmail.com> wrote in message
news:1134205002.878995.88710@f14g2000cwb.googlegro ups.com...
> Manual tranny. VTEC is *not* electronic, it is controlled PER cylinder
> by oil pressure. RPMs go up = more pressure. at a certain point, the
> pins slide in and the intake valves use a different cam lobe.
>

maybe i misunderstand ...

you completely by passed the *EC* (electronic control) part of VTEC
variable valve timing and valve lift electronic control system

The mechanics of the VTEC engaging is hydraulic (oil pressure) via the VTEC
oil solenoid which performs as you describe *BUT* the control of the VTEC
engaging through VTEC solenoid is the ECM which is electronic and uses
several measures to control VTEC solenoid operation {rpm, load, temp,
speed }

> I
> checked when I adjusted the valves, they weren't stuck. But I doubt one
> VTEC being stuck on one cylinder would change the mileage this much.
>

and engine would probably vibrate, seem unbalanced
i was thinking about VTEC solenoid or ECM control signal which would affect
all the cylinders

>
> Driving habits have not changed.
>
> Nope, Oil is 10w30, hasn't changed.
>
> I have the Factory Service Manual, it's pretty useful.
>

well my VTEC electronic info comes from page 5-9
"switchover from one VTEC profile to other is controlled electronically"

so i am just suggesting that one cause for using more gas (your %25 drop in
fuel economy) could be fault in the VTEC control, for instance if the VTEC
solenoid is stuck in high rpm mode all the time then you would be using more
gas, of course i suspect there would be some other symptoms like low rpm and
low end rough starting and rough idling, but once you get into 2500 rpms or
so it would just seem like great performance

I like the HO2S idea too but there should be some performance problems
there as well like rough idling or stumbling or some noticeable performance
problem associated with richened air mixture

Re: 93 Honda Civic Mileage gone bad
 

"jim beam" <nospam@example.net> wrote in message
news:KeSdnTQxHbEVZgfeRVn-gQ@speakeasy.net...
> Danny Beardsley wrote:
> > Manual tranny. VTEC is *not* electronic, it is controlled PER cylinder
> > by oil pressure. RPMs go up = more pressure. at a certain point, the
> > pins slide in and the intake valves use a different cam lobe.
>
> the vtec /is/ applied by oil pressure, but the oil is "switched" on and
> off from the oil channel by an electrical solenoid. that is in turn
> controlled by the ecu. simple oil pressure control is subject to too
> many variables to be reliable.
>
>

that is what i am talking about, i wish i had read this before posting my
rebutal

> > I
> > checked when I adjusted the valves, they weren't stuck. But I doubt one
> > VTEC being stuck on one cylinder would change the mileage this much.
> >
> >
> > Driving habits have not changed.
> >
> > Nope, Oil is 10w30, hasn't changed.
> >
> > I have the Factory Service Manual, it's pretty useful.
> >
>
> non-activating vtec is /most/ unlikely to be the cause of declining gas
> mileage.
>

non-activating may give better gas mileage ?

i was thinking constant-activation, either VTEC solenoid stuck in high rpm
mode, which i supppose effectively becomes manual oil pressure control (is
that a trick to get lower mid-range performance out of VTECs ?)

or the ECM signals causing VTEC engaging are maybe engaging high rpm mode a
bit lower than factory design specs. say engage VTEC at 2500-3000 rpm
instead of 4500

Re: 93 Honda Civic Mileage gone bad
 

Sounds good; will do.

"Michael Pardee" <michaeltnull@cybertrails.com> wrote
> I'd add an OEM thermostat to the list....
>
> Mike
>
> "Elle" <honda.lioness@earthlink.net> wrote

Re: 93 Honda Civic Mileage gone bad
 

"Danny Beardsley" <dbeardsl@gmail.com> wrote
> 200K miles.
>
> Coolant is fine, new thermostat, the engine runs at the
appropriate
> temp.
>
> I'll replace the PCV because they are cheap, but it seems
to work
> correctly.

Do you mean you pinched shut its hose, and within about 30
seconds, you heard it click?

If so, I agree this test is an indication it /seems/ to work
correctly, but it's not conclusive. Its spring wears, for
one, allowing the click to occur, but not allowing proper
throttling.

I estimate my mileage improved 10% to 15% when I replaced
the PCV valve on my 91 Civic at 12 years and about 140k
miles. It was /very/ noticeable, since back then I reset the
trip odometer at fillups and would drive until the fuel tank
was near empty.

Seems like all the cheap fixes (including the O2 sensor)
have been covered. If these don't repair the problem, then
I'd be searching elsewhere.

Of note: Someone in the thread did mention that some parts
of the country switch to a much lower heating value of
gasoline sometime in the Fall, right? IIRC, that right there
will drop mileage on the order of 10%. Also, I don't know
where you are, but where I am, we're having unusually cold
temperatures. My mileage is taking a beating of about 5-10%
lower than it did last year at this time.

Re: 93 Honda Civic Mileage gone bad
 

Rob B wrote:
> "jim beam" <nospam@example.net> wrote in message
> news:KeSdnTQxHbEVZgfeRVn-gQ@speakeasy.net...
>
>>Danny Beardsley wrote:
>>
>>>Manual tranny. VTEC is *not* electronic, it is controlled PER cylinder
>>>by oil pressure. RPMs go up = more pressure. at a certain point, the
>>>pins slide in and the intake valves use a different cam lobe.
>>
>>the vtec /is/ applied by oil pressure, but the oil is "switched" on and
>>off from the oil channel by an electrical solenoid. that is in turn
>>controlled by the ecu. simple oil pressure control is subject to too
>>many variables to be reliable.
>>
>>
>
>
> that is what i am talking about, i wish i had read this before posting my
> rebutal
>
>
>>> I
>>>checked when I adjusted the valves, they weren't stuck. But I doubt one
>>>VTEC being stuck on one cylinder would change the mileage this much.
>>>
>>>
>>>Driving habits have not changed.
>>>
>>>Nope, Oil is 10w30, hasn't changed.
>>>
>>>I have the Factory Service Manual, it's pretty useful.
>>>
>>
>>non-activating vtec is /most/ unlikely to be the cause of declining gas
>>mileage.
>>
>
>
> non-activating may give better gas mileage ?
>
> i was thinking constant-activation, either VTEC solenoid stuck in high rpm
> mode, which i supppose effectively becomes manual oil pressure control (is
> that a trick to get lower mid-range performance out of VTECs ?)
>
> or the ECM signals causing VTEC engaging are maybe engaging high rpm mode a
> bit lower than factory design specs. say engage VTEC at 2500-3000 rpm
> instead of 4500
>
ecu's/ecm's do not get it wrong. they either work, or they don't. and
these honda ecu's/ecm's are spectacularly reliable.

of there /is/ a vtec problem, it's more likely solenoid or wiring.

Re: 93 Honda Civic Mileage gone bad
 

Thanks guys for the VTEC info... I'd always wondered how oil pressure
was stable enough to engage something at a specific RPM. I guess I
better read the factory manual a bit closer. I'll find some way to
check the solenoid.

Re: 93 Honda Civic Mileage gone bad
 

Thanks for the VTEC info... I'd always wondered how oil pressure alone
was stable enough to engage something at a specific RPM. I guess I
better read the factory manual a bit closer. I'll find some way to
check the solenoid.