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Grand prix gtp missfire

2

2000

New member
Hey guys I purchased a 2002 grand prix 40th anniversary and when I bought the car is was misfiring. so I figured it was a bad plug of wire.. so I changed the plugs and wires and it still misfires , I also changed the coil packs and coil module under the coil packs. now I scanned the code and it tells me A p0300 code witch is a random misfire. after a long day trying t figure out when the problem is coming from I found that cylinder #1 and cylinder #6 only get spark occasionally at idle. another thing is the car only misfires at idle not when driving. I also check the vacuum pressure and checked for rips in the hoses and that's all good. Now I suspect this problem to be faulty injectors or a bad fuel pump. I also took all the protector on the wiring harness to see if there are any wires that are corroded and everything is good. If anyone has any idea what could be the problem please let me :)
 


What plugs and gap?

I found that cylinder #1 and cylinder #6 only get spark occasionally at idle
Click to expand...

With that being said, I would say its not a fuel issue if they only get spark "sometimes". But if they are always getting spark but lack fuel, then I'd look into injectors.

Just for kicks, swap that coil with one of the others to see if it follows.
 
The plugs that are used are NGK platinum and the gap is 0.60 the problem was occurring before change all that . I also tried to switch the coils around and that did nothing. And when the car is at idle I disconnected the wire of cylinder #1 (from coil) and there was no spark then did it again and all of a sudden there was spark so its only at random times when there will be spark going threw ( same problem with cylinder #6
 
We can't use platinum plugs in these motors, the ignition system in our cars does not like them. Though that is not the whole problem here, you still will want to swap them out for the factory Delco Iridium spark plugs.

Sounds to me that if when you pull the wire off the coil and you get no spark and it still doesnt change when you swap coils, the Ignition control module is the one at fault here.

Try looking at all the wire for damage or anything that may seem wrong. Its also possible that the "new" ICM that you swapped in was bad from the get go.
 
Another thing I forgot to say is that my car under 1/4 tank of gas the fuse of the fuel pump pops and the car dies... Also what I have notice is that the misfires are alot more rough when the gas is under half a tank ... I don't know if this gives some hints of what the problem could be ?
 


OK I Know its been a while lol but I put new plugs in the car *factory DELCO* and the car still misfires at idle but will never stall on me... I was probably thinking I need to change my injectors do you think that injectors would have fault in an of this?
 
2000 said:
OK I Know its been a while lol but I put new plugs in the car *factory DELCO* and the car still misfires at idle but will never stall on me... I was probably thinking I need to change my injectors do you think that injectors would have fault in an of this?
Click to expand...

Fuel pump relay might be getting ready to take a dump. They're known to go bad on the 97-00 GTP's and cause misfires/no starts.
 
Got anything to scan the misfires with? If so switch the injectors around and make sure they're seated properly and see if the misfire changes cylinders.
 
I scanned it and it told me that cylinder 1&6 are misfires only at idle around 800 RPM so I got new coil packs = nothing also changed the coil pack module= nothing .... I check if all injectors they are all seated properly. So now im thinking that it could be something serious inside the motor. When I went to check out the car before buying it the old owner told me that it misfires so I figured it was spark plugs... when I changed spark plugs and wires I found that all wire were misplaced on the car..
 


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