Missfire Returned 01 Gt

[essikr]

I posted this problem awhile back and thought it had cured itself.It went a week with no trouble.The engine light as well as the other monitor lights are flashing again and the engine misfires.It will stall if you stop the car but will clear if you keep driving.This happens randomly and not every drive cycle.
Items replaced: Cat convertor,spark plugs and wires. Tried running with MAF disconnected but it made it worse. Could the PCM cause this? What makes it come and go?The only codes have been the engine missfire ones.
I read where a ground problem could cause the trouble this car is having?The tranny was replaced in the car some time ago but the problems did not start till 2-3 months later.
My daughter loves the car but I"m at loss to find the problem and she's thinking of trading it. HELP!

[BNaylor]

Don't give up. These type problems can be resolved. Since you've ruled out the CAT and other possibilities I suggest checking out the fuel injectors. Maybe one or more is dirty/clogged or defective. These can de done DIY or just have a mechanic that has the proper fixture to do fuel injector cleaning service.

On the ground, it would be a good idea to check it at the engine/tranny grounding stud.

Other possibilities would be the ignition control module (ICM) and even the coil packs. Coil packs can be swapped out with each other.

Is it a random misfire code P0300 or code consistent with a specific cylinder such as P0301 - P0306?

[essikr]

As I menthoned before the Cat was plugged. The codes the last time read were P0300,1361,1362.
The Cat replacment improved performance when it is not going through the missfire stage. It runs really well when it's not having the problem.
Thanks again for your reply,still a Pontiac man.

[essikr]

Being an old Pontiac service craftsman,I may be able to clean the injectors.What is the procedure? Would't dirty or plugged injectors cause the problem all the time. Is there anyway to check the (ICM)? I don't beleive it to be one cylinder .It seems more electrical,something is causing all the warning guages to flash .

[BNaylor]

Originally Posted by essikr

Being an old Pontiac service craftsman,I may be able to clean the injectors.What is the procedure? Would't dirty or plugged injectors cause the problem all the time. Is there anyway to check the (ICM)? I don't beleive it to be one cylinder .It seems more electrical,something is causing all the warning guages to flash .

You may be on to something there. I didn't recall that you had warning gauges flashing. Which ones in particular?

I'll review the service manual and see what basic checks can be run on the ICM. Some resistance checks can be made with a mulitmeter.

You would think that dirty injectors would cause the problem all the time but I've seen intermittent misfires with dirty injectors too.

[essikr]

The service engine light,the low oil level light and the battery all flash while it is missfiring.
Do you know where the ground straps are located?I looked for them to check but can't see them. There is another thing I didn't menthon about the battery. I had to replace it because the positive side post came apart inside the battery.The car had stopped on her and I went to check the battery connections .The positive connection came out.I don't know how long it was like that or how well the connection was.

[BNaylor]

Originally Posted by essikr

The service engine light,the low oil level light and the battery all flash while it is missfiring.
Do you know where the ground straps are located?I looked for them to check but can't see them. There is another thing I didn't menthon about the battery. I had to replace it because the positive side post came apart inside the battery.The car had stopped on her and I went to check the battery connections .The positive connection came out.I don't know how long it was like that or how well the connection was.

For all ground wire termination, check out the driver's side of the engine/tranny where the tranny mates up to the engine. This will be radiator side not firewall. There will be several wires at the grounding stud. Can't miss it.

[essikr]

Your right could't miss it. I cleaned and tightened the ground there and the battery ground. This may be dumb but with auto headlights at night do they go out while you start the car?
Tried to get the codes read again at AZ,they told me if the service engine light wasn't on they could not read them. ADV said they don't do it.
The car started to miss while idleing in my garage but it quit before I could get the hood open. What causes the gauges to act up when it's missing?
Can't give up now it's become a quest!

[BNaylor]

Originally Posted by essikr

Your right could't miss it. I cleaned and tightened the ground there and the battery ground. This may be dumb but with auto headlights at night do they go out while you start the car?
Tried to get the codes read again at AZ,they told me if the service engine light wasn't on they could not read them. ADV said they don't do it.
The car started to miss while idleing in my garage but it quit before I could get the hood open. What causes the gauges to act up when it's missing?
Can't give up now it's become a quest!

Yeah, same here on AZ. They require the SES light be on. I thought by now you would have got yourself an odb-ii scanner. I have an Actron CP9145 and it sure comes in handy.

Miss during idle sure sounds like an injector to me.

Anyways, on the idiot lights that is a head scratcher. Do they all come on and flash at the same time? This sounds more like an instrument panel (IP) problem. There is a logic decoder in the IP which routes light commands to the respective lamp. If one or more the diodes short in the decoder then it could give a similar indication. You can remove the dash bezel and drop the IP cluster and check the wiring. There are two electrical connectors which may be loose or need reseating.

[essikr]

Back again! car still does it's misfire routine randomly.I noticed that not only do the engine monitor lights go on and off but all the instuments are affected while the car is misfiring. It will not idle during the misfire and if you shut the key off and restart it,it runs normaly again. I've looked for loose connections ,battery connections ,grounds etc. nothing seems out of place. I can't help feeling this is an electrical problem that causes the misfire and the gauage and light malfunction. Don't know where to look next. My daughter still has my Bonneville and I want it back!

[BNaylor]

Originally Posted by essikr

Back again! car still does it's misfire routine randomly.I noticed that not only do the engine monitor lights go on and off but all the instuments are affected while the car is misfiring. It will not idle during the misfire and if you shut the key off and restart it,it runs normaly again. I've looked for loose connections ,battery connections ,grounds etc. nothing seems out of place. I can't help feeling this is an electrical problem that causes the misfire and the gauage and light malfunction. Don't know where to look next. My daughter still has my Bonneville and I want it back!

Well it is starting to sound more like an electrical problem so I agree. Have you checked everything in the engine compartment fuse box like reseating fuses and relays? Have you tested voltages at the battery and alternator. Whatever problem you have maybe affecting the PCM module. What does the tach reading do?

[richtazz]

In the original diagnosis, before the problems returned, did the ignition switch get changed? With all the odd electrical anomalies, it sounds like it could be the problem.

[jimmyv-21]

i agree with rich- it could be the ignition switch, since everything is electrical. maybe an alternater acting up??? as far as the grounds i had a similar problem in my 98 s10. the guages were not dummy lights but they would jump around when the truck misfired. come to find out, the place where the grounds are bolted to are painted at the factory, thus the grounds have to work throught the paint. i scraped the paint off, retightend, and havent had the problem since, at least not the electrical part. double check your battery connections at both the battery ends and the other ends to make sure they are good. sometimes it helps to take them off and clean them even if you dont see any corrosion. the other day there was a post on here of a car with some weird electrical probs. we all put in our .02 and come to find out it was corrosion under the battery cable where she couldnt see. my ex's malibu would act up on the highway- guages flashing, then the car would die. but no misfire- it ended up being the alternator. it sure sounds electrical though. if you are still wanting to clean the injecters, try this:
http://www.automotiveforums.com/vbul...d.php?t=513171
good luck

[BNaylor]

Although it is a possibility, I'm not convinced the ignition switch is the main or the real problem. I have never seen one on a Grand Prix cause misfires. Normally, you will have starting problems, the engine will die or shut off, or you will have various accompanying symptoms like no blower motor, headlights blinking on/off, no DIC display, no cruise control, no turn signals, no DRL lights, etc. Not necessarily all of the symptoms.

I would check MAIN IGN # 1 and 2 circuits with a multimeter and see what the voltage is which will also include looking at the ignition switch input and output. Also, check the PCM 12v and PCM Sense lines.

Hate to see this guy go through all that hassle and find out he has another problem other than the ignition switch. Just my 2 cents worth.

[richtazz]

ok Bob, I was just wondering, because I wasn't sure what all the signs of a failed ignition switch were or if it were something that was tried the first time the problem mysteriously cured itself. I would agree that it sounds like a wiring or ground issue.