baffling fuel issue

[nismoautoxr]

Back story is as follows . the car has been flawless for 3 years for the most part ....LS1 swap in a road race car doing mostly HPDE stuff and some TT. Its using a MS3 with MS3X and using a MAF as the primary algorithm . The MAF is a card type GM sensor (frequency type). It has been fine . Things are always good till they aren't and now they aren't. The last track weekend it ran great on Saturday then on Sunday it started to have a high RPM miss starting around 4100 RPM. The logs show that something is terribly wrong with the PW and the MAF frequency above 4100 RPMs. It is rock solid below that and it is very consistent that it starts at about 4100.fAt first I started focusing on RPM signal since it was so RPM related but looking at the log I only see the PW and MAF abnormality. I have a known good crank sensor, a bank of 4 coils , and a MAF sensor so I went to the dyno so sure Id be able to get it narrowed down. NOT!!!. I swapped the crank and MAF sensor as we were doing pulls and then I substituted one bank of coils at a time and the problem still persists. I don't get it . I'm a little lost on this because the frequency MAF is a little under supported in the manuals . I just cant imagine why it would have gone all this time and been flawless and then boom ...its not . That typically leads me to a failure when that happens. Here is the tune file and a log. see what you guys see because I need a fresh set of eyes . this thing is wearing me out and I really want to be at Road Atlanta on the 19th....9days from now

[Matt Cramer]

It seems to be getting noise on the MAF frequency sampling. Are you able to get an oscilloscope on the MAF output to see if there's any intermittent weirdness there? If not, try decreasing the MAF averaging lag factor and see if that helps.

[nismoautoxr]

I agree with you Matt and that is something I didn't think of (reducing the lag factor) . I will toy with that if need be but this just came from no where and it seems to be getting worse and worse. I wish I had caught on to what was actually going on when I was on the dyno but I didn't and scoping it on the street while driving it is gonna be dangerous and maybe impossible since it doesn't have a passenger seat for a helper. I took a potshot at it by replacing the maf since it was pretty cheap . I'm going to do some basic DVOM checks on the related wiring tonight. Failing that I may have to whip up a speed density tune to get me by.