I'm pretty much in the dark when it comes to tuning. I'm starting up a new build and have very rough running and severe backfire....
SBE LQ4, L92 heads, LS3 stock intake and injectors. Custom cam and bench tune by EPS.
Upon startup, everything was good. Fired immediately, idled smooth, sounded good with open headers. This was only about a minutes worth of time. I didn't even have coolant in it yet. After a few short startups it started running rough and backfiring really bad. I thought maybe because open headers. Few days later, got loose ends tied up including the exhaust on. No change. It backfires and won't idle. I changed plugs. #2 & 4 were BLACK. Tried again. Holding rpm around 2000, and entering CL, the LTFT on bank 2 goes to 25%. Bank 1 at 12%.
Why would they do this?
Did I screw up by starting a few times with open headers?
If so, why would only 2 & 4 be so black?