Question about 2003 Pontiac Grand Prix

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I own a 2003 Pontiac Grand Prix GT. It has the 3800 Non Supercharged engine. My problem is that it runs VERY VERY badly (as if it's missing on several cylinders) on MOST (but not all) mornings until it reaches full operating temperature and then smooths out and runs perfectly. Some mornings this does NOT happen for some strange reason but at least 85% of the time this behavior takes place. Sometimes it displays the code that mentions trouble with the Crankshaft Position Sensor (i cant remember the exact code) but sometimes the codes are all CLEAR, nothing at all. I have changed MANY parts trying to solve this issue. Sometimes I think I have it solved but all of a sudden after two or three weeks of running just fine it starts missing badly again, until reaching full operating temperature. I have changed the Plugs, Wires, all 3 coil packs, Ignition control module, Crankshaft position sensor, Camshaft position sensor, Upper intake Manifold (the plastic thing, was leaking in one small area). Please help if you can

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  • ajweysham Sep 25, 2009

    Hey there, thanks for your reply.. I probably should have also mentioned that I have brought the vehicle to the Dealer and two other mechanics shops (goodyear and a local guy) and no one can see to nail down the problem. The dealer took one look at my aftermarket coil packs and refused to work on the vehicle saying that the after market parts COULD be the source of the problem. Would you recommend that I go ahead and change the aftermarket coil packs to AC Delco parts and then go from there? or is this dealer being ridiculous? Goodyear is the one that changed the crankshaft position sensor and the camshaft position sensor based on the code that was for the crankshaft position sensor. The local guy blamed it on the upper intake manifold leaking saying that he could "hear" it leaking. The dealer also mentioned that the upper intake would need to be changed. I did this work myself since this is my third 3800 with the same intake trouble (seems they ALL go out close to 100K Miles).


    Knowing this extra info, where would you say i should start? Continue buying parts? Which parts would you suggest me getting first? sorry for 21 questions, I'm just at the end of my rope with this thing, it's really becoming a hassle and I'm wondering if further damage is occurring by me continuing to drive it in this condition. I'm certainly no mechanic although I can usually handle most relatively simple repairs so many parts I really dont know the technical names or technical functions of them until I look them up and read as to how to replace them. So if you could tell me exactly which parts you would change first if it were you i would seriously appreciate it..


    thanks again..


    al

  • ajweysham Sep 25, 2009

    I'm going to try the suggestions from fordexpert but does anyone else have any further suggestions I might try also.

  • ajweysham Sep 25, 2009

    Hey there.. thanks for your reply. I bought the aftermarket coil packs simply because thats what freakin autozone was selling at the time.. There was No other reason other than the cost vs the OEM product. I had Goodyear do the work on the crankshaft position sensor and the camshaft sensor and they CLAIM that the learning procedure was done. ALSO, when the dealer refused to work on the vehicle because of the "many aftermarket parts" (which is ****) they CLAIM that they verified that the learning procedure was indeed run (but I have no proof of this at all). Honestly, if I had some idea of HOW to run it that would probably be the first thing i would do since I understand that it's sortof a "timing like" issue with that sensor. As a matter of fact, both before and after the crankshaft position sensor was installed the computer had the same code displayed which led me to believe that either goodyear did not change the part or they did not run the learning procedure like they claim. The dealer said that the aftermarket coil packs COULD possibly be causing this supposedly erroneous code. I thought about changing them to AC Delco parts but I don't want to continue to throw parts at the dang thing without a clue as to whats the issue. By the way, fordexpert mentioned that it might be a poorly performing alternator and that a way to test this would be to turn off the AC when it starts missing. I tried that this afternoon but no luck with that. So, I'm assuming this is not the issue.

    any help would be greatly appreciated..

    al

  • ajweysham Sep 25, 2009

    Thank You to KCGTODAD but from what I have been told the learning procedure has been run. (but i can't prove that.) Anyone else have any ideas to try?

  • ajweysham Sep 26, 2009

    Thanks for your reply.. are you saying that it would work properly when warm and not when cold or the other way around? The car seems to run very badly when cold but once it warms up it runs just fine.. I will certainly give the ECM a try though, sounds like it's a very good possibility since the codes are reading crankshaft position sensor if the ECM uses that info to determine when to fire..


    Thanks!

  • ajweysham Sep 26, 2009

    I just looked up this part. Over $400 and there's no guarantee. Is there any way to test the ECM to determine if it truly is the problem? I'm ok with buying the thing if thats the problem but if it turns out NOT to be the problem I'm going to want to pull whats left of my hair out! Any ideas on how I could determine if this is truly the issue? It makes sense to me that it would probably be the issue but I just dont want to make another costly mistake..

  • ajweysham Sep 28, 2009

    blueextc3221 seems to be on to something with the ECM but this is quite an expensive part to not know for SURE if this is the real problem. Can anyone tell me a way to TEST the ECM before replacing it? Im assuming that a part like that is not returnable if it turns out NOT to be the correct part. Am I correct in that assumption?

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My son had one when he was attending university and had not exact issue but similar, we live up in the mountains and when he leave to class he stat the car and go try to be on time, but that took him more time in the winter than in the summer, we tested the car and no one can find the problems, they just appear when it wants to and after keeping a log we discovered that this car need to be warm at all times to operate good, the computer does not function good until it reach the temp. that needed. We found out that in the summer it is less and less problems if any than winter…we took the thermostat out just to test it and he drove to town without one, he never put one again in the car since…the car get worm faster and no problems were noticed since then…many will disagree on this approach however I am giving you a real experience and it is up to you to diside…let me know how that work for you and please do not forget to rate my service so we can improve on it with your help. God bless

Posted on Sep 28, 2009

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Could be your fuel injection pump. It may not be working optimally when cold and runs OK when it reaches a certain temp and above.

Posted on Sep 26, 2009

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  • Master
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ECM (engine control module) may be faulty. It uses the Crank/Cam sensor info to determine when to fire. If it has bad solder joints - they will expand after heated, and not work properly. Seems like it is the only thing not replaced :D Thanks for using FixYa!!

Posted on Sep 25, 2009

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  • Expert
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Hello! I have owned/repaired several 97-03 Grand Prix's both L67 and L36. If you have aftermarket coil packs (I'm assuming MSD), you aren't gaining anything from a performance standpoint over the OEM packs. Are they the source of your problem? I doubt that, too. However - did you by change have a CASE learn procedure after you did the crankshaft position sensor replacement? I would have that done.

Hope this helps and good luck!

Posted on Sep 25, 2009

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  • Pontiac Master
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Sorry to hear about repetitive problem. The 3800 engine was one of the best GM ever made.
There are 3 areas to look at. The engine has a cold start circuit. It relies on info it gets from an air temperature sensor in the airfilter ductwork and a water sensor. Both tell the car it is cold. It will not increase idle or enrich the fuel like it needs to on a cold start.

The second item is an evaporator cannister switch. This switch is meant to pull in fuel vapors from the start. It can cause a vacuum leak if it is broke and runs mainly on startup to clear excess gas vapor.

The third item which should have coded would be a bad oxygen sensor. When parts start needing to get hot to work, they are "lazy" because it takes them so long to finally work.

Your mentioned coding. I do not know if you are taking it to Autozone for testing or doing it at home. But maybe you could drop your car by Autozone early in the A.M. and then have them scan the engine when it is cold later in the afternoon. Wish I could point to one thing, but you seem like you understand how many things can affect your vehicle.

Let us know what you found so we can help someone else with the info.

Posted on Sep 25, 2009

  • fordexpert Sep 25, 2009

    Did you happen to keep the old coil paks? You would have an option to switch the coilpak and return to the same dealer or go to a different place.



    I would try Autozone or Oreillys for a free scan. See if they list a cold start solenoid, if it is not using the onboard computer to increase RPM. Tell them also you want a water sensor not for the gauge but for the cold start circuit. The air sensor looks like a matchhead, hit it with a hairdryer to see if it helps.



    Another thing that does not cost anything is to put your A/C controls on Off when you start the car. Get your Alternator and battery checked on the car, as some of the electronics trip at different volts.

    Low voltage may not give good spark and it will take a few minutes to build up, which you assume is the "warming up" time.



    Let me know what helped.

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