Ok, I am asking this for a friend who is literally at the end of his rope with this car. I know almost everything about the car because I have been there for most of it. Quick Specs are: 385ci LT1, M6, LS1 style LTCC Coil per cylinder ignition with Opti used as crank sensor, LT1 intake, Lazer Cams (I think this is all correct) .529"/.522" 228*/234* 112LSA, Ported LT1 casting heads, and lots of the little things.

The specific issue that we're having is that the car has a stumble at ~2000rpm and has a loss of 10psi of fuel pressure at the exact moment the stumble occurs. I'll try to be very descript here so that you can imagine the problem. Whether in gear or in neutral, at ~2000 rpm the motor starts to modulate the RPMs in a very short range like between 1900 to 2100rpm, the car will then get an errant reading from the MAF sensor of 250gps or greater (up to 441gps) and will proceed to dump fuel into the cylinders as if it has gone WOT. The injector BPW goes from about 5mS to 35mS as soon as the MAF thinks that its seeing 250+gps. This in turn seems to suck the fuel rails dry and there is a recorded loss (visually) of 10psi on the rail. Strange I know. And everything was actually recorded, the stumble, using Datamaster. This is still OBD-I using a professional OPEN LOOP tune from one of the boys over in Detroit, but I don't remember the name of the place it was tuned at. The car did make 426RWHP and 404RWTQ so the tune isn't necessarily somthing that should be in question, the guy is extremely well versed in tuning many many vehicles.

I have provided a screen shot of 4 consecutive frames from the Datamaster stream so you can see the before and during occurences of the MAF/BPW/MAP and any other important readings.

The only thing I find really strange about all of this is that the O2's never really record a drastic change. With all that raw fuel being dumped into the cylinders you'd think they'd spike and go completely whacko with so much unburned fuel.



Anyone??