4th gear missfire

[Juanmiguel]

The GTP is having missfires in cylinders 1 and 5 only when cruising at around 55mph in 4th gear, specially if going up hill. If you shift into 3rd it will go away and it does not missfire under any other type of acceleration, not even WOT.

It does missfire in all cylinders while idling, but that I guess it's because of the cam.

I think I've read about similar cases before here in the forums, but I can't find them right now. Anyone know why this may be happening?

[BillBoost37]

Typically it's ignition/tune up related. High load, low rpm in high gear. That's when the system works it's hardest.

[Juanmiguel]

I see, the plugs are a couple of months old (AL104s). The wires have over a year maybe. I could try the wires first I guess.

[reesez]

my truck used to do that after i mushroomed an exhaust valve. would miss and jerk while in od. no other time. then if i put in drive it was fine.

[dsmuts]

I thought you sold your gtp?

[Juanmiguel]

I thought you sold your gtp?

I did, to a close friend. I still help him out with this kind of stuff.

[BillBoost37]

my truck used to do that after i mushroomed an exhaust valve. would miss and jerk while in od. no other time. then if i put in drive it was fine.

This is a 3800 though. Valve issues are not very common. Igntion/tune up is the most common cause of this type of stuff.

[Tony Mendez]

Have someone put the car in reverse and brake torque it while you spray the coils with a spray bottle of water and see if the misfire develops. If it does, you may have a cracked coil(s). My advise has always been to replace the coils and module as a unit, if within your budget.

[Juanmiguel]

Thanks, I have a couple of spare wires to swap for the missfiring 1 and 5 cylinders. I will also try spraying the coils.

Sent from my GT-S5830L using Tapatalk 2

[reesez]

This is a 3800 though. Valve issues are not very common. Igntion/tune up is the most common cause of this type of stuff.

true, but i did read about chipped pistons and thought maybe id throw a personal experience in there. it was a v6 and auto. just saying.

[BillBoost37]

My only issue with throwing other motor experiences in is that the OP may end up going after that and wasting time/money/effort on something that is super uncommon with the motor he's working on. Like if someone had suggested a head gasket, it's so uncommon it's one of the last things you suggest/test for.

I try to aim the person at the most common and constant issues. That's all. Didn't mean it in a bad way.