Thread: Really strange, tried everything - surging, bucking, stalling

This started out as a minor issue, where the car would stutter, but has gotten worse the more I try to fix it.

The car is a 1998 Pontiac Grand Prix 3.1 SE

Currently if I idle the car at 2000 RPM, it will stutter and buck, and sometimes stall. If I attempt to drive the car, same thing. It's virtually impossible to drive.

I've replaced:
Spark Plugs & Wires
Air Filter
Crankshaft Position Sensor
Fuel Pressure Regulator
Fuel Filter
Harmonic Balancer (it was wobbling, so it seemed a good idea)
I've run fuel injector cleaner through it
I've put HEET in the gas tank thinking bad gas

I haven't yet replaced the Fuel Pump because that's a last resort, it's more expensive than all the stuff above. The SES light is not on.

I connected a Fuel Pressure sensor, and disconnected the vacuum hose from the regulator and plugged the hose, then idled it at 2000 RPM, and the gauge didn't move much when it stuttered, etc, it just flickered. When it went to stall, it dropped a little. I thought it strange that the lights inside flickered, etc, but it only dropped to 1000 RPM, not stalled. It sounds like it might be an electrical problem, maybe? I'm tired of replacing parts and not gettin anywhere.

What I *WANT* to do is take a match to it and enjoy the firery glow.

Suggestions? Comments? Thoughts?

Thanks for your time,
Robert

Have you checked lims, icm, or coilpacks?

Sorry, don't know what "lims" is.

I've put it in drive, and revved it as hard as I can without it squealing away(yeah right), and it didn't buck at all. Let off the brake, and then it did it(That was a little earlier on) - it also never does it when backing out of the parking place, no matter HOW hard in reverse I go. To me, that's REALLY strange.

I hadn't checked coils because I've read online that it's EXTREMELY unlikely for them all to go at the same time. I'll look into them after the ICM.

Haven't looked into the ICM. Will try to troubleshoot that next. That could be possible because it would affect all of them, and possibly cause the lights, etc, to dim, if there was a short, I assume.

I forgot to mention that I've checked for vacuum leaks with spraying water, and finally using carb cleaner, after disconnecting the TPS, and couldn't hear any RPM changes. The vacuum gauge is steady at idle.

So, ya'll don't think a fuel pump is the likely culprit? Could a faulty O2 (after cat) cause any of this?

Thank you for your quick responses.
Robert

Which crank sensor did you replace, your car has 2 of them? Check the crank sensor on the back side of the engine and the harness that runs between it and the ignition module real good. It is not uncommon for that harness to melt on the EGR pipe or exhaust manifold and cause issues. Also make sure that when you replaced the harmonic balancer that it is installed all the way on, or the front crank sensor will not read correctly.

All the coilpacks dont hav to go bad to cause big running issues. I had one coilpack only quit on one terminal and the car drove like @#$%. If you think its rare for any to go bad i have a bucket of bad coils, both sc and non sc. And lim=lower intake manifold

Haven't had chance to try any of this out yet, I will this afternoon.

I replaced the crank sensor behind the harmonic balancer. I made sure (as tough as it was) to make sure I wired it the same way it was before, including putting the plastic stud thing into that tiny little hole behind the air conditioner. I got the harmonic balancer on there pretty good. As far as I could tell it's on there good and all the way on. If it were not, wouldn't it always cause a problem? The car ran fine for a couple days after I replaced it and the crank sensor. But I will check on the wiring on both. Why on earth would it have 2 crank sensors? Isn't one enough?


Wasn't doubting you, l67ss, I know they go bad, I've replaced one on my 2002 G.P. I'm just thinking for all 6 terminals, or 3 coil packs to go bad at the same time would be rare. When I replaced 02's, it had an SES light. Is it possible for one to go bad, cause the car to be nearly undriveable, and still not throw a code? It sounds like it might be a useful idea to buy a new coil pack, and swap it around to see if the problem goes away. Or I could swap it out with the other Grand Prix I have and see if the problem goes with it. Now that would be fun. (I checked, they use the same one) The more I think about it, the more this could also be the problem, if the entire coil pack went bad, then two cylinders would be misfiring, that would be noticeable if 1/3 of the engine wasn't running right. Come to think of it, I did spray water in there looking for a vacuum leak (seemed safer than ether or carb cleaner), if one of the packs has a crack in it, it would definitely show up then. The car did run much worse during the rain. But that still could point to a bad ICM.



Thanks again for all your help, I really appreciate it, you've given me ideas I hadn't thought of before. I was thinking it was fuel related, and ya'll got me going toward ignition troubles.
Robert

Like i said ive had have a coilpack die. On my current engine i had one completely die with no ses, no miss at idle. It just cut out under throttle. And had horrible mpg lol

I swapped a known good coil for each, and the misfire occurred on each. It didnt change any making me think that its not two that are bad.

Nuts, I would have bet that was the problem.

Did you look at the wiring from the ICM to the rear crank sensor? I have seen the harness melted on the EGR pipe or exhaust manifold on more than 1 vehicle that would run fine at low RPMs but barely run or die at higher RPMs. It runs off the front crank sensor at low RPMs, rear crank sensor above 1600 RPMs

This is why I dread working on cars.....

I rotated the good coil from a running 2002 Pontiac G.P. with all three on the 1998 Pontiac G.P. Both are SEs.

The problem continued. Very predictably at 2000 RPM the problem would show up within 5 minutes. On the whim, I decided to try leaving the one good coil, and brought over a second good coil, and rotated it between the two suspect coils. Problem still existed both times. At this point, I was fed up, and decided to try something else, and put all of the coils back to where they were originally. Then for the heck of it, I tried to get the problem again - what the heck. It didn't misfire.

I backed up, put it in drive, it didn't misfire. Now, at this point, I'm shocked. This car ALWAYS would have the misfire. Without exception. Now it's gone? I drove the car around, pushing it hard, trying to get it to misfire again, and it wouldn't.

Then another strange thought, maybe, just maybe I got the coils mixed up and the bad one is on the 2002 car. Drove it around, didn't do it.

Went back to the 1998, sprayed some water, and it misfired. Dried off the coils, and it hasn't misfired since.


I find it hard to believe swapping around coils fixed the problem. Is it possible I exorcised some demon? The wife drove it to work, and for 2 weeks she hasn't been able to do that without having it at least ONCE misfire. NOTHING.


I did see the wire you're talking about. It's possible in all of this I shook it loose from the exhaust pipe. I did also notice that the coily type of plastic GM uses to "protect" wires from heat was very brittle and was crumbling. I'm thinking that could be the problem. I've seen water on coils cause problems before, and that may have been looking like the misfire.

I did "reseat" the cables on the ICM, just to see what condition the plugs were in, etc. (they're fine, btw), and at that point I might have freed the wire from the exhaust pipe.


Is it possible to replace the wire between the rear crank sensor and the PCM? Is it easy to do or does the car have to be in the air?


Thank you both for your help, and giving me ideas to try. Your kindness has certainly saved a car from being "accidently" ignited.

Robert

Wife just reported the problem has returned, gonna look at that rear crank sensor wire again. I'll replace the wire and see what happens.

found the wire ya'll were talking about. it had about 4 inches completely melted. occasionally, it would make contact with the exhaust, causing a short, and the misifre. i pulled the wire and cut the plugs off and then attached wire between that was an equivalent gauge. enclosed it in some of that wire insulator and routed it well away from anything hot. car is running fine.

this is exactly why i wont buy GM again. it would have at the most cost another dollar to route it differently, but no, they decided to route something that melts through something that gets very hot and narrow.

so, after spending close to 200$, turns out 10$ bit of wire and insulator fixes the problem.

Once again, thank you both for your help.

Robert

It was originally routed to the rear of the engine and in 2 clips, one at the back of the head and another on the block. what normally happens is a less than thorough mechanic disconnects at least one of the clip and does not re-install it. I would not say that that is GM's fault. I'm sure if they planed on the wire being closer to the exhaust they would have wrapped it with a higher temp conduit. I would also say it is not GM's fault that you misdiagnosed it and spent all the additional money.


I work on all types of cars ever day and there are many vehicles I would not buy, but this generation Grand Prix is not one of them. There are however many newer GMs and just about every other makes I would never own.

I never blamed GM for me misdiagnosing the problem. That's my fault for not going to this forum earlier than I did. Only for leaving a wire so close to hot metal. This is in combination for a faulty transmission, which IS something that I've had to replace in this car many many miles ago. It wouldn't shift to overdrive, and would throw a SES light(causing it to fail MD emissions, of course). I forget the code, but when I googled it, it was a well known problem with this and similar year/model cars. I even triple checked before I bought the 02 to make sure it was fixed in that year.



Related question. I seem to remember in all my googling, that a misfire could damage the ICM. It's now experiencing hard to start when hot. Could driving it with the misfire caused by this wire being damaged cause the ICM to be damaged? I remember that's one of the symptoms of a bad ICM. After trying a couple times it finally starts. It's not a new symptom, I just figured this would go away with the wire repair.

ummmmmmmmm nevermind. Replaced the starter after seeing the spindle (don't know if that's the right word) pop out and go back before the key was released.

Still starts a little oddly, but since I had the battery disconnected, the cpu memory is empty.

Thanks again for all your help.