I could try to get back to the original fuel pump but because it's runnig rich and not lean makes me think the fuel pump is not a problem. I'm going to replace the fuel pressure regulator first, although I can't explain myself how a bad regulator or something bad in the fuel system at all could cause running rich irregularly? When the FPR fails it not regulates the fuel pressure correctly and makes more fuel to pass than it should be, am I right?
The only one constant is the problem appears after similar RPMs every time.
Anyone has an idea what else from mechanical side would be good to be replaced?
Unless I am not reading your graph correctly, it looks like it is running rich AND LEAN. There are two "spikes", one up and then one down. So it looks like it goes very lean (upwards spike) , then very rich (downwards spike). Perhaps it is the lean condition causing the problem? When it goes so lean, the computer is overcompensating and you get the momentary richness until the computer catches up? (remember, no O2's online during WOT). Computer should really react faster though. Can you hear any noise when it goes lean? Any knocking?
Since it happens at a certain rev range, I keep thinking less fuel pump/FPR and more CPS/Vanos. Something that causes a running change. Cam timing would do that. Have you run the Vanos test on the computer?
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