Guilty1s

Series 2 rb25
-stock ecu
-fresh stock motor
-3" FMIC
-Freddy IM
-vented Bov, I know but it's not the issue
-running wastegate pressure
-zero boost leaks


New motor to us. Drove it around for a couple day fine. Pulls real hard. Then it will start hesitating. Pretty much fuel cut as far as I can tell. May be spark cut but I don't think so, wideband read lean during the cut. What is making it so hard to diagnose is that it is intermittent. Turn the car off. Turn it back on, it is fixed, pulls like a champ. It may last 10 seconds, it may last 10minutes. At stand still, when the issue is present, won't rev past 2000 something rpms.

My first assumption was MAF, it fits.Have put 4 other e60 mafs on there and act the same situation. I checked all the wiring and it checks out fine but it is hard to be 100% since it is an intermittent issue.

I am using ecutalk and everything looks fine.
-coolant temp in check
-cycling o2 sensor
-perfect tps
-base timing as expected
-maf reading as expected but it does hit 5v on a WOT pull. I didn't think a stock rb could do that at 9-10? Psi. The butt dyno tells me only about 260hp maybe?

Here is where I find it gets interesting.

I put a new ecu in it. Boom. Fixes it. Swap back to the old one immediately to make sure it's not a fluke, runs like shit again. Put the new ecu back in. Run good, Like 2 small burps for a split second in about 2 days running perfect otherwise. Then the same exact issue comes back.

That's where we are at today where we swapped the old ecu in today and it runs fine for now, but we expect it to start it's intermittent problem again...

Any ideas?
Learning LT or ST fuel trims odd or something?



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