for HyundaiTech
 

this is a follow-up to your reply (reply below)

I took the car to another garage that did an inspection

the guy said there's no compression in one of the cylinders (the third one)
he said it's either a ring or the head
how long/hard is it to fix this? is it just easier to find a used engine and
replace the whole thing?
if I continue to run the car this way, can the engine break completely?

also, there's some oil seeping through the front (not a lot, and the oil
level is good in the engine). how serious is this?


your reply:
*****************
The dealer could be onto the problem. It's debatable whether it needs the
computer. Well, actually, it's all debatable, but here's what tends to
happen.

The idle servo controls the amount of air entering the engine. If it
cannot adjust the airflow down to the proper amount for idle, the
injectors start trying to cut the fuel, causing the rpm's to vary. This
could be because of a misadjusted throttle body, bad idle servo, or bad
computer.

What has happened sometimes on this engine is that coolant will leak from
the coolant passage in the throttle body into the idle servo and corrode
the windings. If it creates an open circuit, no problem, replace the
servo, fix the leak and move on. But, if it creates a short circuit, it
will kill the engine computer from too much current. I have opened some
of these computers to find a black mark on the inside of the case
indicating the location of the flame.

While I doubt the computer is needed, I'm really in no position to second
guess someone who actually looked at the vehicle and performed a
diagnosis. The most important thing here is to make sure that if there is
a throttle body coolant leak that it gets repaired too, so the problem
doesn't happen again right away.

I wrote:
*****************
182000 km on board, 4 cylinder engine
problems started recently

these are symptoms:

when starting car, engine RPM surges to 3000, after a few seconds drops to
1000. every time it drops to 1000 it surges again to 2000 and keeps
oscillating until I put automatic transmission in gear. when it is in gear
engine RPM drops to a stable 1500 RPM, which is high for idle. engine is
always pushing car forward and I must press brakes very firmly to keep the
car in place.

when acelerating, there's no problem. there's no problem on highway either.

however, when breaking, or if I let the car slow down on it's own, when it
drops below 60 km/h the RPM starts oscillating again. in order to stop the
oscillations I either have to break or give it a little gas. it seems that
as long as the engine is under load it is fine, but when it's running freely
at "low" speeds (under 50-60 km/h) it oscillates between 1000 and 2000.

it's as if the engine thinks it will stall so it pushes the RPM high, then
realises it is too high, drops it and thinks it will stall again.

first time the problem appeared, it went away after a couple of days,
however the problem was reversed: idle RPM was too low, around 500, and the
car was slowly backing up on an incline instead of staying in place as it
should. it also stalled when I reached the end of the driveway and stopped
giving it gas.

what could be wrong? the dealer wants 1500 to replace computer and "servo
control" or "servo control valve", whatever that is, however I doubt he
knows what the problem is.

Re: for HyundaiTech
 

You have no compression in one of the cylinders and the car has normal
power at highway speeds? This is difficult to believe.

If true, the 2nd repair facility hasn't yet performed enough testing to
determine the source of the lack of compression. A technician can perform
a cylinder leakage test by introducing compressed air into the cylinder
through the spark plug hole while the valves are closed for that cylinder.
If there's no compression, the air should leak out of the cylinder
somewhere. Through the intake or exhaust indicates a cylinder head/valve
problem. Through the crankcase indicates a piston/ring problem. Through
the radiator usually indicates a severely warped cylinder head. All of
these repairs will be quite substantial in cost. I would expect no less
than $1500. To find out for certain where the problem is and what will be
required to fix it, the cylinder head must be removed and the head, block,
and pistons inspected. I also wouldn't be racing to purchase a used
engine unless I knew there was some catastrophic failure or a serious
issue with the block. You have no idea the condition of a used engine.
With your car inspected, you'll know what condition the engine is in.

Well, actually, you'll only know that if the facility checking your car is
competent and honest. So far, the dealer's diagnosis is much more in line
with your symptoms than the second facility's. You report stable idle in
gear, normal acceleration, and normal highway driving. No compression
should cause a misfire, resulting in a vibration at idle, very poor
acceleration from a stop, and reduced power and horrible fuel mileage all
the time.

Re: for HyundaiTech
 

Sorry. Forgot to mention in last post. Driving with no compression in a
cylinder isn't good for the engine because large amounts of unburned
gasoline will get into the oil. There are possibly other hazards of
damage depending on the specific reason for no compression.

If your dealer's diagnosis is correct or partially correct, which I
suspect it is, the idle servo could short out and fry your computer,
making the car undriveable.

Re: for HyundaiTech
 

"hyundaitech" <howitsac@nospam.hotmail.com> wrote in message
news:34ac3c0fbcc532345dd50430f1afadfa@localhost.ta lkaboutautos.com...
> Well, actually, you'll only know that if the facility checking your car is
> competent and honest.

well, I dunno... the guy said he needs to do more tests to find out the
problem, but that there's no compression in the third cylinder (doesn't know
why. maybe he just tested it with the error-code scanner?)

I will take it to a second hyundai delaer but I'm afraid they'll give me a
third reason for my problem...

> So far, the dealer's diagnosis is much more in line
> with your symptoms than the second facility's. You report stable idle in
> gear, normal acceleration, and normal highway driving. No compression
> should cause a misfire, resulting in a vibration at idle, very poor
> acceleration from a stop, and reduced power and horrible fuel mileage all
> the time.

while in gear and stopped, the idle is stable but high. while in gear but
the car slowing down under it's own power (no brakes), under 60 km/hr RPM
fluctuates between 1000 and 2000
acceleration is as "normal" as it could be for a 9 y/o 4 cylinder 140hp
engine... I can't say it's normal, just that it's not striking me as
horribly slow.
at highway speeds, I get no problems.
sometimes the car does vibrate at a stop.

while stopped and in gear I have to press the brakes hard to keep the car in
place because the idle is at 1500, so I guess I can't say I have very poor
acceleration from a stop.

also, depending on the temerature outside, the idle oscillations could be
between 1000 and 2000 (very wild) or just between 1800 and 2200

Re: for HyundaiTech
 

To determine a cylinder has no compression, one must do a compression test.
This is done with a compression tester/gauge and cannot be accomplished
with a scanner. It is possible with a scanner to isolate a misfiring
cylinder, but it's not possible to determine the cause of the misfire to
be no compression without an actual compression test.

Everything you've posted leads me to believe you have no misfire (or if
you do, it's only at idle), putting tremendous doubt on the no compression
diagnosis.