2002, Camaro, Z28, LS1, Automatic, Cam, Stall, Stock exhaust, 125 shot wet.

The car has been dyno tuned by a reputable tuner.... The car ran perfectly fine until a couple of nights ago. Started it, took off to head home, and it was cutting up, backfiring out of the exhaust and it has been doing it since.. if you hammer it, it will always do it and it will intermittently do it under normal driving conditions... if I pull up to a stop light and stop sometimes it will backfire while just sitting there, if I make the converter lockup and lug the car, it cuts up and backfires.

The upstream 02's have been replaced
Cam Position and Crank Position Sensors Replaced
Visually inspected valve springs
Plugs have been checked
Wires and Coils have been checked
Fuel Pressure has been checked
Checked for vacuum leaks


Watched the live data and misfire's on a scanner and everything looks normal to my knowledge and it is not showing any misfires, I've used 2 different scanners just to eliminate the possibility of the scanner not reading correctly. I've pretty much run out of ideas at this point... I may replace the plugs, wires, test spark out of the coils but it doesn't really feel like a miss (misfire).... it almost seems like it's loading up..

Any help is greatly appreciated.

 

Did you test the fuel pressure while driving it? It may be ok at idle, but not ok under load or at WOT....

 

Did you happen to get gas right before it started to happen?

 

Does it run better if you unhook the MAF?

 

Did you check your nitrous system for leaks? A bad solenoid leaking n2 and fuel into the intake will cause all sorts of problems. You should be able to see something change while data logging if you are experiencing backfires.

I'd close the bottle then purge all the pressure then take a section of your intake downstream of where you have it plugged into your intake. Check for obvious leaks. If you don't find any I'd keep the nitrous off and data log again to see if the misfire goes away

 

Yes, I left the gauge hooked up while driving and pressure remained around 58 even while it was cutting out etc.

 

He did get gas before it happened but has since fill it up with 93 from a reputable gas station.

 

Same problems whether the MAF is plugged in or not.

 

We have not checked the nitrous system for leaks although the bottle has been closed and lines emptied via the purge. It is a zex kit with the WOT box, the only solenoid is the purge. I will look it over tonight when he comes by.

 

Does it feel like one cylinder or multiple cylinders? Ive seen coils run fine at idle and when they load up it will misfire.

 

Honestly, I can't tell if it feels like only 1 cylinder or if it's multiple. If you hammer the car, it runs perfectly fine. It's mainly when the torque converter locks and you lug it, it cuts up and back fires and you can feel it missing. Mainly when it's under a load.

 

Do you have a wideband hooked up?

 

I would borrow a set of coil packs from a buddy as they take 5 mins to change. I had a similar issue with my vette that was not throwing any misfire codes. I swapped coils with my truck and the problem went away.

 

Other possibilities:
- leaky injectors,
- coils as mentioned above;
- CKP reluctor spins on crank.

 

Sounds like a spark-coil-wire problem. Take a peek at night with the engine running you may see the problem.

 

On the older VW's we used to spray them with a squirt bottle with water. Found cracked coils real easy with that method.