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I have been chasing an abnormality in my Magnacharged '01 Vette for a while and could use some new ideas. The car runs very good in all modes except for part throttle with RPM between 2000 and 2200. When there, the right bank goes lean and the car stumbles. I have replaced the front O2 sensors, checked engine grounds and visually inspected wiring and ignition. An ideas would be appreciated. And if someone can tell me how to attach a scan and/or a tune to a post, I would be glad to do that.
Ok I figured it out, scan attached.
Note that whenever the RPM is between 2000 and 2200, wheather moving or stationary, a large variation can be seen in the STFT's. Right bank gets a big POSTIIVE correction to make up for the right side O2 sensor lean indication. This is enough of a 'leanout' to be felt, which feels like its dropping 2-4 cylinders. I made one 2nd gear WOT pull which looks pretty good.
Any ideas?
How did you tune this? Your VE is lean at 20-30 MAP & 2000-2400 RPM. If you did a VE table tune, fatten up those cells and test again.
Tune attached. As you can see, my VE is actually a bit fat in those cells plus the real brain teaser is, why does the right side lean out to the point that the engine stumbles??
Could this indicate a bad PCM??
Judging by the uniform numbers in the VE table, it wasn't tuned with a w/b. Try fattening up the values in the affected areas. If that doesn't resolve your problem, I'd suspect a slight intake leak or perhaps a bad injector.
Thanks for the reply. I have considered the intake gaskets and injectors, but it doesn't make sense that the lean condition would only exist at 2100RPM, but it could be due to some other variable coming into play. Oh yeah, it only does it after the engine is throughly warmed up, ie, run for at least 30 minutes. If pulling the blower wasn't such a chore I would have done that by now, but if I can't come up with anything else, I'll just have to go ahead and do it.
Before you commit to a bunch of work, fatten up those VE cells by 10% and test again. That's a lot easier than pulling the blower..