92 Chevy Lumina jerks, cuts off

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.

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Don't dismiss the possibility that the control module its self is on the fritz. I had a similar car from 1990 that eventually went to the scrap yard due to problems just like this.

I'm pretty sure the years of oil soaked wires had something to do with my problem, but the problems sound very similar.

Slap the computer with an open hand with the engine running. If starts the engine bucking you have found the problem (likely). My cousin works at a GM dealership and he says it's a quick test to see if something's wrong with the computer. The wire between the crank sensor and the ignition module needs to be in good condition as well.

Good luck. I know I'd be weary about buying another W body from that era again. They had a number of problems... the ignition control being one of them.

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Thanks for the reply. I did have the control module changed and that fixed everything for two weeks. Now its slowly going back to the way it was.

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I also own a 92 Lumina, and I had a problem with 2 cylinders cutting off intermittently for a bit then coming back on. I replaced the control module and 2 coil packs, my mechanic explained that if they weren't changed together, bad coil packs would kill the control module and vice versa. Later I experienced the car dying at stoplights, but would restart ok. This turned out to be a bad crankshaft sensor and cracked connector to it as well. Hope this info helps. Roy

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Mike, what diagnostic codes do you get? s

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This problem has never generated a code, nor has it ever triggered the engine light.

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I had a bucking problem with a Ford Crown Victoria back in the 80s. I never did find the problem and eventually traded the car for a Toyota Corolla.

---MIKE---

>> (44 15' N - Elevation 1580')

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Don't apologize. Detail is a lot better than the people that post that their car does not run, so what's wrong with it.

What happens if you put the car in neutral when the problem starts? Will it go away? You've already identified that it will run fine in reverse so let's explore tranny interactions a bit more. Admitedly Mike, I'm just poking and hoping a bit here, hoping that uncovering some more data points will reveal something.

--

-Mike-
snipped-for-privacy@alltel.net
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Thanks for the posts all :) Roy Bragg's post seems to be the correct answer. Although I have not taken it back to a mechanic yet, I believe there is a short in the wire between the control module and the crankshaft position sensor. If you'd like to read more on the reasons I've determined this to be true, read my other post on rec.autos.tech : http://groups.google.com/group/rec.autos.tech/browse_thread/thread/d81d3573cb7f3651/18ec1e141e739fc8?lnk=raot

Thanks all

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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.

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