One cylinder is pig rich - GM Reflash PCM (LS1)

What could cause one cylinder (#2) to run pig rich while all 7 others look almost perfect?

The cylinder is always about 200 degrees cooler than the others. I suspect the other seven are actually slightly lean because I've been tuning with a WBO2 in the middle of the X pipe.

I've swapped injectors, and the problem stayed with the cylinder.

I leaked the cylinder, and it only has 6% leakage.

I've swapped coils and it made no difference.

I've checked the wires, and they appear to be correct. This is a 24X swap of sorts. It's an L21 BBC with Chevy firing order (1-8-4-3-6-5-7-2) controlled by an LS1 PCM. The 2-3 and 7-4 swaps of the LS1 firing order are reversed in the wiring.

I have a spare PCM that I want to test next.

i would be trying the pcm for sure then checking valve train next

Regards Ross

Bit of a long shot, but what exhaust setup are you using, the SB with 5&7 linked in a tri-Y used to cause air flow and fuelling problems?

More likely is the way Ross is thinking - if the fuel seems to be right, then it may not be getting enough air - something may be affecting the breathing, either in or out, that is preventing the required amount of air getting into the cylinder. If you should be using a flat-tappet (if so, why?), you may have wiped out a lobe, or both!

I'd start with a careful visual check, then using a DTI on the spring retainers/caps to check they're all opening the same, intake to intake, exhaust to exhaust - fortunately it's a relatively easy job on these engines, if you fab' up a simple mount for the DTI base, if required.

Oh, a slight mis-fire will also colour the sparp plug, and mean a lower pipe temperature, so I'd swap spark plugs and coils if there isn't a valvetrain issue. If the engine uses leads from the coil(s) to spark plugs, I'd check resistances and swap them around, too, if possible.

I think I found the problem, and possibly solved it. The rocker on #2 intake was just a hair past zero lash. The pug hasn't fouled yet, and the temps on the primary tube is at least 200 degrees hotter (almost as hot as the others now). The engine seems to run better too.

I had not touched the rockers since I lashed them on the stand, so I re-lashed them all to half a turn. It's definitely quieter now too!

I should have done this sooner, but I dreaded taking off the valve covers. Turns out it wasn't that difficult after all.