Ls4 random misfire on every cylinder when warm with no codes thrown

[Greasymonkey]

Need a little help or advice on where to trouble shoot next. Its a 2007 Grand Prix gxp which is all stock besides a k&n filter. I'm having an issue where the car has a noticeable miss when driving in 3rd or 4th. It doesn't throw any codes. While taking a log and monitoring the misfire cycle it will usually have a miss on multiple cylinders. Every cylinder usually has a miss at some point. It's never consistent with which ones are missing. The plugs are brand new as are the spark plug wires. Both o2 sensors have been replaced. New throttle body, gas pedal, map sensor and a new catted downpipe. Fuel pressure is at 57.9 psi, mass air flow seems to be reading normally from what I understand. DOD is disabled. Any help or advice would be appreciated. Thanks.

I will attach the log soon. Thanksgxp misfire 2.hplgxp misfire.hplgxp misfire 3.hpl



Also want to add it’s only when light throttle driving normal. WOT there is no miss or hesitation.

[5FDP]

For what it's worth the fuel pressure channel will always read 57.9psi because it doesn't work. You'd need to manually check to see what your fuel pressure is and it will vary, it's not possible to always be at 58psi 100% of the time.


Being that it's only in 3rd and 4th I wonder if it's transmission related, like the torque converter. What happens if you turn off the torque converter when it hits 3rd or 4th gear?

[Greasymonkey]

I’m planning on checking fuel pressure at the rail tomorrow with a gauge. The transmission was rebuilt, in the logs attached in also monitoring the Tcc slip when it is engaged. The thought has crossed my mind but I was sure if that was causing the misses. I have not tried turning off the converter yet I will give that a shot tomorrow as well. I appreciate the reply!

[Greasymonkey]

The issue is resolved. I had too much converter slip while it was engaged. Raised the minimum tcc values and no longer have the misfires or slight shuttering. So with that being said is it possible to have excessive torque converter slippage while engaged that will create a false misfire or was it truly missing? Either way I appreciate the advice. Thanks