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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / March 2006

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92 Chevy Lumina jerks, cuts off

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Mike_D - 18 Mar 2006 20:32 GMT
I hope that my lengthy post will not discourage anyone from reading it
and trying to help, but I was hoping giving as much detail to the
problem would help...

I've had an off and on problem for two months that is driving me nuts.
It all started when one time I was sitting at a light and I noticed the
RPM fluctuate and the car cut off, started right back up no problems
and ran fine. A couple of days later I was on the freeway and the car
bucked a couple of times. I was hitting about 2000 RPM and the tach
would jerk down to 500 then back up.  As time went on, the frequency
increased. If I'm driving it bucks/jerks but not enough to cut the car
off (since I'm giving it gas). If I'm sitting at a light, of course it
will make it cut off.

Ok, so I take it to my usual mechanic and ask him to give me a
diagnostic for 70.00. He called a few hours later and said he noticed
when he was checking the wires to the control module, that he was
getting ready to unlatch one of the sets of wires and the car stopped
the bucking.  He determined that the wires, the connector or the module
itself may have a short in it or that maybe the wire connector wasn't
tightly in there socket.  But it does run great now.  So I picked up
car up and was happy I didn't have to buy any parts.  It ran 100%
perfect for about 2 weeks solid.  Then I noticed the bucking deal
slowly started back up. Started out once a day and only for a split
second and never again.  As time went on, the frequency would increase
to maybe a quick buck a couple of times an hour.  But as long as it
wasn't bucking, it would idle sooo smoothly and have great performance.
Heck I could even step on the gas at 55 and make it downshift and get
it to 75 in 2 seconds. The torque would whip my neck back into the
seat.

 So I decided to inspect the wires he spoke of. I unplugged it. The
connectors were extremely clean, no dirt, corrosion and they looked
brand new in fact.  The wires themselve were in fine condition as well,
no cracks, etc.  But I hooked it back up and the car did not buck for
another week.  So over the next two months, it go to the point where if
the car started acting up, I would just go through the motions of
pushing the connectors on tighter.  Even the they were on tight and
they would not wiggle with any play whatsover. Not even a micro
millimeter of play. There were on so snug, that I don't really think me
pushing on the connectors was doing anything, but nonetheless, just
going through the motion of doing it, seemed to fix the problem.  So a
couple of weeks later, I'm having to do this twice a day it seems like.
Heck now I'm starting to really wonder if its all just coincidence and
I in fact wasn't really making anything happen.  Then a month ago, it
got to the point where it would never buck or cut off at idle, but
anytime the gas pedal is pressed, it had a chance to cut off or buck.
I remember twice (different days) that it would start up everytime with
absolutely no problems, but the second i put the car in gear it would
cut off.  I could sit in park and rev it and it behaved and reved
normally.  But the instant I put it in gear it would die. It was
something else forcing it to die, because even if I stepped on the gas
a little or a lot before I put it in gear, it would still die.  But the
weirder thing is at the same time, if I put it in Reverse, it does not
die. I was able to hold my foot on the brake and it had full torque. I
could even burn rubber on the tires.  But putting it in Drive, 2 or 1
would make it cut off immediately.

At this point it's getting dangerous to drive because its too
unpredictable, so I figured I'd have him go ahead and replace the
module. I thought that maybe one of the pins inside the module itself
could have a short or be loose.  I figured while he was at it I'd have
him replace the O2 sensor since I never had it replaced before.  So
this was about 3 weeks ago. He replaced the module and O2 sensor.

The car has ran beautifully since I've had it replaced and I patted
myself on the back for getting it replaced.  No bucks, no misses,
nothing. Even with 180k miles on it, it still has great power and runs
smooth.  So its now going on week 4 and its starting back up again.
Slowly but surely.  A week ago I was approaching a stop sign and it
just cut off without warning, but started right back up and did not do
it again until 2 days later.  Occassionally sitting at a light, I can
sometimes see the RPM all of the sudden do this big fluctuation and cut
off.  If I give the gas about 300 rpm extra, its enough to keep it from
cutting off.  But its not all the time, its random.  Like yesterday I
drove it and it cut off at 3 different lights within 10 minutes. As far
as I can tell, at this point, it won't buck while driving it, only at
idle or very low driving range (like keeping it at 35 where you barely
have to press the gas).

Any ideas?  I strongly believe there is no short in the wires to the
module itself. If I move them around, jiggle the connectors, etc while
its running, there is never anychange to the way the car behaves.
Iceman4757 - 19 Mar 2006 00:35 GMT
My friend has a 92 Lumina as well and his was doing the exact same thing as
your car is doing. It all started for him when his fuel pump when out in his
car and so we put a new pump in and the ECM wasnt getting power. So after
taking everything apart, we found a wire was shorted out that runs from the
battery term box on the drivers side to the ECM which supplies power, the
short was located in the wiring harness that runs up near the frame near the
passanger side headlights. After a week the car started bucking and
backfiring after awhile and so we changed fuel filters, O2 sensors, wires and
plugs, and even had the coil packs and control module checked for trouble.
After each of these things it would run for a week or 2 before it would act
up. We finally decided to check the wiring harness out one last time before
we went and bought a PCM and low and behold, there is a wire that runs from
the crankshaft sensor to a plug in for the harness that had a short and when
it would touch the frame of the car, it would ground itself out and start
chugging and bucking. We repaired the wire and it has been 8 weeks and no
problems. Have your mechanic or youself check the wiring between the
crankshaft sensor and where it plugs into on the harness.  You can unclip
this section of wiring out and do the repair yourself if thats the problem.
It sure sounds like the same exact thing and I was told by a friend of mine
who works at an autoparts store that shorting wires are not uncommon on the
Luminas. Hope this helps!

>I hope that my lengthy post will not discourage anyone from reading it
>and trying to help, but I was hoping giving as much detail to the
[quoted text clipped - 79 lines]
>module itself. If I move them around, jiggle the connectors, etc while
>its running, there is never anychange to the way the car behaves.
Mike_D - 19 Mar 2006 01:31 GMT
Thanks for the reply. This sounds promising...  Its just so puzzling
that before I had the module changed, I could wiggle wires on the
module (even though they didn't actually move) and it would run fine
for a day to a week.  Then after the module was changed, it stopped for
2 weeks and started back up.  If the wires to the control module and
the wire to the crankshaft position sensor are pretty close then this
just might explain why messing with the wires would cure it for a
while...

If anyone still has some input please let me know, thanks.
dnoyeB - 20 Mar 2006 16:22 GMT
> I hope that my lengthy post will not discourage anyone from reading it
> and trying to help, but I was hoping giving as much detail to the
[quoted text clipped - 79 lines]
> module itself. If I move them around, jiggle the connectors, etc while
> its running, there is never anychange to the way the car behaves.

EGR Valve/System - 90% probability
Fuel pump - 10% probability

Mechanic sucks / shop not paying enough to keep experienced mechanics -
100% probability.

Signature

Thank you,

"Then said I, Wisdom [is] better than strength: nevertheless the poor
man's wisdom [is] despised, and his words are not heard." Ecclesiastes 9:16

Mike_D - 21 Mar 2006 03:02 GMT
Thanks for all the replies people.  If not for this group, I probably
would be poking in the dark for a while and for my mechanic to pinpoint
a short in the correct wire could have turned into many visits.  Well,
since having the module changed, I have never bothered moving the wires
around the control module because I figured that changing it had fixed
a possible short in a pin in the module.  My post mentions that
everytime I moved those wires, that it would run fine for a few days.
Well sure enough after reading Iceman4757's post, I decided to go out
and move the wires a little again, just to see if my problem stopped
again. Sure enough it did. It ran with no bucks since the post (2
days).  Today however, it started back up, without warning. This time,
it was shutting off at every light and would not stay started unless I
kept my foot on the gas a little.  I was on my way to work... When I
got to work, I left the engine running.  I decided to do an experiment
to confirm the wire Iceman spoke of could have a short in it.  Instead
of reaching down from the top of the engine and moving the wires to the
control module around, I decided to lay on the ground and grab them
from the bottom.  I grabbed them and pulled them forward towards the
front of the engine.  Sure enough the second I did that it cut off and
would not start.  I got back down and pushed them back toward the
transmission (attempting to make the wire move away from the metal
block/frame).  It started right back up and I drove it for 2 hours now
with absolutely no problems.

This also explains why that one day it was cutting of in forward gears
but not reverse. The reason would be that when you put the engine in
Drive, the engine torques backwards. When its in reverse the engine
torques forward.  That very slight movement of the engine was probably
enough to make the wires touch metal again.  After moving them around,
it wasn't cutting of in Drive or Reverse anymore.

If anyone is reading this trying to find a problem in their car and
this sounds like a winner, and you are not sure which wires I have been
moving around, I'll explain... If you follow the spark plug wires from
the engine, they all connect into a big black box.  The module is
behind that.  There are a few connectors to that box as well. 2
connectors on one side, and one on the other.  The side with the 2
connectors (passenger side) is the wires I've been moving around :)
Mike_D - 22 Mar 2006 21:32 GMT
Took it to mechanic today and explained why I believe there was a short
in the crankshaft wire, he came back out within 1 minute and said
"You're not gonna believe this".  He pointed to a yellowish wire that
was hanging between the transmission pan and the engine (on passenger
side, directly behind the frame of the car by the wheels). About a full
inch and a half of the insulation on the wire was gone. The wire had
the metal of the transmission pan on one side and the metal of the
engine on the other. The gap between both sets of metal was only about
1/4-1/2 of an inch.  So if the wire only would have had to move 1/8 of
an inch in any direction to make contact.  He sprayed the dirt off the
wires and taped it up with electrical tape (Free).  Drove it home just
fine.  This was only an hour ago, so it's too early to say it's fixed,
but I got a strong hunch it is.
dnoyeB - 23 Mar 2006 20:57 GMT
> Took it to mechanic today and explained why I believe there was a short
> in the crankshaft wire, he came back out within 1 minute and said
[quoted text clipped - 9 lines]
> fine.  This was only an hour ago, so it's too early to say it's fixed,
> but I got a strong hunch it is.

Nice.  Though I hardly think electrical tape will last very long.  Keep
us posted.

Signature

Thank you,

"Then said I, Wisdom [is] better than strength: nevertheless the poor
man's wisdom [is] despised, and his words are not heard." Ecclesiastes 9:16

Comboverfish - 24 Mar 2006 07:10 GMT
> Nice.  Though I hardly think electrical tape will last very long.  Keep
> us posted.

No doubt, especially considering the likely oil leaks on the back
(side) of that block.

Oil is no friend to electrical tape, particularly when wrapped around a
greasy wire in a confined space with oily hands.  I would replace
(solder in and shrink-wrap) any and all compromised wires and loom them
for a longer lasting repair.  It's really worth the extra time.

Toyota MDT in MO
dnoyeB - 24 Mar 2006 15:14 GMT
>>Nice.  Though I hardly think electrical tape will last very long.  Keep
>>us posted.
[quoted text clipped - 8 lines]
>
> Toyota MDT in MO

Yea, and look at another car of the same type/MY to see how that wire is
run.  Its probably in some convolute or something covering/protecting
it.  Perhaps some clamps broke off as well.  Need to get that wire back
to its original path.

Signature

Thank you,

"Then said I, Wisdom [is] better than strength: nevertheless the poor
man's wisdom [is] despised, and his words are not heard." Ecclesiastes 9:16

 
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