I'm working on a 2002 Trans Am and it has an issue I can't figure out. Customer dropped the car off for a tune but the car is rough to say the least and needed more than a tune. The cheap ass chinese y-pipe was in the back seat and needed two hours of fab work to install, needed the right plugs in it, and the car looks like it's hit everything but the lottery. He did a cam swap and has no idea what cam he used, 01D030x injectors from Racetronix, ebay headers, and a 6 speed swap.
It had a dead misfire in it on cylinder number 3. I swapped the coil and it's gone away except an occasional PO353 code but no noticeable misfire to go with it. Whether open or closed loop, once warmed up the Bank 1 O2 sensor reads considerably leaner than the Bank 2. Even in closed loop the STFT can go to 20% and see very little change in the O2 reading. Plugs all looked good, I've switched O2 sensors side to side with no change, moved injectors side to side, new plugs, verified fuel pressure, looked over wiring, verified grounds on the back of the head. I'm pretty much at a loss on what to do here. Looking for suggestions. I've attached a couple log files to help. Any advice is greatly appreciated.
I have had a similar issue on an LS1 intake. Initially it was just happening cold then as it warmed up things expanded in the right places and it all sealed up. Over a fairly short period it got much worse. Intake manifold seals took care of it.
This is sounding more like a burnt valve or some other mechanical issue. Have you run a compression test? It might save you from spending a lot more time on a lost cause.
Sadly you will have to pull the heads to see if you have a wiped cam lobe and/or destroyed lifter. And it doesn't have to be completely rounded, it just takes a little to be out of balance with the rest of the motor. If you have checked everything else then it is time to remove the head and look for this:
I forgot to update this a couple weeks ago. So after a laundry list of little issues I finally got it straightened out. The intake seals were crap, small vacuum leak at the back of the manifold, two bad coils, wrong plugs that were all fouled anyway, and a loose ground on the back of the head. The final piece of the puzzle was the female terminals in the coil harness connector. They were bent just enough to where they weren't making solid contact. I bent them back into place and it fired on all 8 consistently. I was able to tune it with no more issues.
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