Missfire Returned 01 Gt

:confused: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!

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?

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.

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 .

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.

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.

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.

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!

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.

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!

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?

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.

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/vbulletin/showthread.php?t=513171
good luck

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. :2cents:

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.

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.

Not a problem Rich, we agree most most of the time but not all of the time. This post has a long history starting with another original post. It started out as a typical misfire problem but looked like it evolved to a CAT since it is in that year category but then he mentioned these coincidental electrical problems. The CAT helped but did not solve his problem. This is just a continuation and with all our heads combined maybe we can help him resolve the issue. So I am aware of the history to a point. Just FYI. Later.

Thanks guys for the input.Heading out to the garage this evening to battle with the beast.I will try all the suggested remedies and tests and give it another go.
The iginition switch has not been changed and I agree with Bob it doesn't act like the switch.I think the tach is reading the fluctuating rpm's ,not sure .Something was flashing in the heads up but I didn't catch what it was. It usually doesn't last long enough to see everthing.

Thanks guys for the input.Heading out to the garage this evening to battle with the beast.I will try all the suggested remedies and tests and give it another go.
The iginition switch has not been changed and I agree with Bob it doesn't act like the switch.I think the tach is reading the fluctuating rpm's ,not sure .Something was flashing in the heads up but I didn't catch what it was. It usually doesn't last long enough to see everthing.

Well hopefully you can find a common point to the problem. Do you have the GM Pontiac service manual? If not I can send you a few pages of possible circuits to check. Just let me know.

OK, this is what I did let me know what you think.
Cleaned battery terminals and connectors ( it is a new battery)
Removed grounds cleaned and re-fastened
Removed connection to the ignition module,spray cleaned and secured connection.
Made sure all fuses and relays were secured and seated
opened air box and loosened connection to PCM ,re-seated connection and secured .
checked all visible plugs and checked for proper connection.

The car has not missed for six days now and there is a noticable chage in the transmission shifting. It is much smoother than before. For what it's worth ,there is a difference. Fingers crossed the car went a week before without a problem than failed again.
I am leaning towards the PCM connection or the PCM, what do you think?
Thanks again for your help.

It sounds like you're on to something, I'll keep my fingers crossed too, although it makes it hard to type!

Not enough crossed fingers! It's still there,it ran well for almost a week. My daughter took it to the dealer .He cleared the codes Po300,1361,and 1362 but could not find the problem,Would not act up while it was there. The same codes are back. Can the ICM cause this problem intermittently? It has been suggested that it icould be the problem. AZ says they can test it if it is off the car? She doesn't want to go back to the dealer if she doesn't have to.Don't know what else to do!

If you do take the ICM to AZ or Advance, make sure they run the test enough times to get it warm to the touch(6-8 runs normally), as the circuits can be fine when cool, and fail after they get warm.

ICM tested Ok, they ran the test more than 6 times and it was good. Can the PCM cause a problem like we are having? Almost ready to buy one. AZ can order one .for just over $100. They also sell a used one removed from a matching vechile for $125 with a 1 year warranty.
When it is misfiring ,backfiring and popping if you shut it off and restart, it runs OK again.

ICM tested Ok, they ran the test more than 6 times and it was good. Can the PCM cause a problem like we are having? Almost ready to buy one. AZ can order one .for just over $100. They also sell a used one removed from a matching vechile for $125 with a 1 year warranty.
When it is misfiring ,backfiring and popping if you shut it off and restart, it runs OK again.

Worth a shot I guess. Also, check with Ed Morad. He posts on Ebay. I've seen PCMs for $50 outright no core exchange. Make sure it is for your model GP and year.

The PCM may need re-programming for your vehicle when you get it. The VIN and model, etc. is stored in it. PCM replacement normally requires a crank variation learn (Case Learn). This stores the low and high settings of your crank and CKPS into the PCM. Otherwise you may get false misfires.

Have you checked with the dealer to see if you need any PCM updates? It may just need a re-flash. A TSB is out on the 3800 concerning re-flashing the PCM if you get misfires with no other causes. Good luck!

Checked with Morad and he has one. I found a service bulletin 02-09-41-091 ,it states that a module that has had VIN information entered into it (one from another vechile) cannot be reprogrammed .VIN information can only be entered into new modules. Do you know if this is true or is this something they tell you so you have to buy new?
What is the difference between a re-program and a re-flash ?Is the CASE Learn something it does on it's own or does the dealer have to do it? I will check the dealer about any PCM updates. What does the TSB say about the misfiring? Thanks again for your help.

Checked with Morad and he has one. I found a service bulletin 02-09-41-091 ,it states that a module that has had VIN information entered into it (one from another vechile) cannot be reprogrammed .VIN information can only be entered into new modules. Do you know if this is true or is this something they tell you so you have to buy new?
What is the difference between a re-program and a re-flash ?Is the CASE Learn something it does on it's own or does the dealer have to do it? I will check the dealer about any PCM updates. What does the TSB say about the misfiring? Thanks again for your help.

I'm not sure if that is true but it sounds flaky. The dealer has the capability to re-program/re-flash the PCM to include the VIN data. Re-flash and re-program are the same. The problem with not putting in VIN data is a Tech II machine will not display the proper menus to run any further tests if you ever take the car in for service at a GM dealer. Check with the dealer and see if they can re-program the PCM since there may be program revisions required anyways.

The case learn must be done on a dealer's Tech II machine. No other way to program case learn info. I did it with my re-programmed PCMs.

Another option is to get the used PCM from Ed Morad and send it to either DHP (Digital Horsepower) or Intense for programming. They do have the capability to do all of this plus insert your VIN number. DHP charges around $214 and Intense around $90 for basic programming. This is a good route to go although more costly because you will be able to keep your original PCM just in case. What if the PCM is not the problem? Also, this disproves that a module that has had VIN information entered into it (one from another vehicle) cannot be reprogrammed.

I'll check on the TSB info for you when I get a chance.

Thanks Bob ( hope this is your name) .Can i put the PCM from Ed and try it without programming or CASE Learn. Would it work OK to check and see if the PCM is the faulty part?

Thanks Bob ( hope this is your name) .Can i put the PCM from Ed and try it without programming or CASE Learn. Would it work OK to check and see if the PCM is the faulty part?

All my friends call me Bob. Yes, as long as it is for your model and year GP which I am assuming is a GT it should work without the case learn. Case learn is recommended but not mandatory. Purpose is just to sync it with your engine crank settings and not someone else's parameters. When I got my re-programmed PCMs I was able to start the car and run it. I took it in for the case learn just for assurance and the recommendation from DHP and Intense. Wouldn't want any false misfires causing problems. When you first install the new PCM it will take a few seconds longer to crank over. It will cure itself and re-learn on the subsequent start ups.

Out of curiosity what is Ed charging you for the PCM? Good luck!

So not to be confused does that mean it will work without having it re-programmed? The $55 he wants sounds well worth it if it really is the problem or helps eliminate it as the problem.
Is there a way the dealer can tell if it's bad if we have him check for updates and re-program the original?

Is there a way you can tell if the replacement is from a 2001 GT?

Unless you are getting a SES light with stored DTC error codes dealer probably won't be able to determine the PCM is bad, however, they can check for any updates and see if you need them.

Get the GM part number off it first and post. You cannot use a PCM from a GTP they are programmed different. Likewise you cannot use one from 97 - 98 models.

1999 and up to at least your year model should be the same.

I went to see Ed today to get the PCM. He is really a nice guy,his race car Grand Prix turns 9.46 147 mph in a quarter mile, WOW fastest one in the country.If this doesn't work he is going to fix me up a care package with all the ignition parts.He has a lot of parts for Pontiac's especially Grand Prix's. He took the one i got from a 2001 gt while I was there. Going to try it tomorrow.

I'd bet your injectors are the culprit to the misfires. My GA had them for ever, cleaning them a few times helped but in the end, I just bought all new ones and I hav not had any misfires since.

Fyi-- before I did the new injector install, I blew out the entire fuel sysetm(main and return), you wouldnt believe the crap that was in there! Dont know how it all gets by the filters. Good Luck!