01 GT 3.4L Tune-up and still Cyl.5 misfire

[JBramley26]

I recently had to change my head gaskets on up on my 01 3.4. Got all that done and 20 to 30 mins after running it i got a service engine soon light and checked the codes and have a P0305 which is a cylinder #5 misfire, I changed the plugs and wires, code went away for about 10-15 mins and is back now. I swapped out the coil pack with 2 good ones and no change. I checked the ohms on all the injectors which all check in range. The car runs, idles and drives just fine. Im beating my head against the wall on this, thinking about getting a used ignition control module and see if that does anything. Any help would be greatly appreciated. Hope everyones New Year is off to a good start.

[grandprixgtx00]

a P030x can also be caused by low compression. since you just changed the headgasket that would be my first suspicion. i would check compression on cylinder#5 and see what you get.

did you torque the heads down to spec?

[JBramley26]

I will do a compression check tomorrow and let ya know. I did the torq. specs and sequence correct, i have torn this motor apart at 37K and now at 113K for head gaskets and intake gasket failures. Thanks for the quick reply.

[tempfixit]

If you get a low psi reading, try squirting some oil in the clyinder and retest. If it raises the compression you have failing or lined up rings.

[grandprixgtx00]

Originally Posted by JBramley26

I will do a compression check tomorrow and let ya know. I did the torq. specs and sequence correct, i have torn this motor apart at 37K and now at 113K for head gaskets and intake gasket failures. Thanks for the quick reply.

Yeah, I'm not a huge fan of the 3400 myself. i had a 2004 Grand Am GT with the ram air...bought it with 10 miles on it, and traded it in at 30,000 miles cuz i had nothing but problems with it.

but do the compression test and see what you get. I've seen these motors go at 100,000 miles many times before.

[lilwhitelude]

Find someone with a scanner that can read data. See how often you misfire. Pull the plug and compare with a plug from another cylinder.

[JBramley26]

Well i performed the compression check, Cylinders 1-2-3-4 & 6 are 160-170, cylinder 5 is 140. All the plugs look the same but they have only been in there for 3 days and about 100 miles. -Lilwhitlude, what type of scan tool would i need to see how often I'm misfiring? Would it be the GM Tech 2 Scan tool cause i wouldn't even know where to get one. Thanks all for your inputs and please keep them coming.

[lilwhitelude]

Any descent scan tool will be able to give you a data stream. I have a cheaper matco scanner that does just fine. Even a actron scanner, not a code reader, but scanner would work.

[JBramley26]

An update, after doing the compression check i put the plugs back in and fired her up and now its miss firing hard, shaking and shuttering the vehicle. In park i give it some throttle, smooths out but in gear its a no go. It wasn't doing this prior to me checking the compression. I also have the rotten egg smell coming out the exhaust now as well which would be a plugged up cat. I feel like Im going around in circles with this thing. Hope everyone had a good weekend.

[grandprixgtx00]

before the headgasket was done, was it leaking internal or external? if you had an internal coolant leak it could in turn cause the cat to go bad if you drove it around for a while. It also has the potential to ruin the bank 1 sensor 1 o2 sensor too.

did you get the codes cleared? if so...what if any codes came back up? If it is a bad cat...it could also cause a P0305.

[consultIII]

sometimes when doing headgaskets or intake manifold gaskets the fuel rail o-rings into the intake get disturbed and cause a vacuum leak and lean misfire. these o-rings are dry and seal air from the manifold. spray brake cleaner into the #5 injector area and see if idle changes or may hear air sucking into the manifold as the fluid is sprayed over the leak...if yes check the o-ring for not being seated properly.

[JBramley26]

Alrighty guys, don't know why or how really but here's what i did. After the compression check and engine running like crap, i went back and removed the coil packs again and swapped them seeing if the problem would follow which it did, i've never seen a coil pack like these have a problem on just one cylinder but it did for me. Replaced it and cleared the codes and so far so good. Thank you all for your help. Greatly appreciate it. grandprixgtx00, I did have an internal leak and i will be replacing the cat just to avoid problems down the road. consultIII, thanks for that bit of info. on finding leaks around the injectors, when i did the heads and intake gaskets the intake was crack and i swapped it out so i replaced all the o-rings on the injectors and fuel rails, but doing what you said and no problems there. Thank you all again for your help, this site and you guys have helped me out tremendously.

[JBramley26]

Well new update, Cylinder 5 misfire is back. I did go out and get an Actron CP9176L Auto Scanner and tried using the freeze frame data and it would say error connecting to the computer. Just so no one has to re-read everything. Ive got a 3.4L, changed out head gaskets recently @ 113K miles. New plugs and wires, took the service engine light away for about 10 to 20 minutes, Cylinder Compression for 1,2,3,4, & 6 are 160-170 and #5 is 140. The car was running smooth when i did the the tune-up but now it seems to have a shutter. any help would be greatly appreciate guys. Hope you all have a good weekend.

[grandprixgtx00]

have you checked out the cat? if you have access to a heat sensor gun, test the cat. put the car in the air and see if the cat is running real hot.

[JBramley26]

i do have a heat sensor gun and will do that tomorrow, thanks for the quick response grandprixgtx.