BobMachus

I went on a nice spirited drive up into the mountains and back today. I was having a blast. I had Craig Moates diagnostic software running, but not logging data. I was VERY low on fuel (1 bar) and my passenger noticed my BLMS were 160!! (this means VERY lean). About 3/4 mile later I pulled into a gas station to buy gas and the idle was a bit rough. I filled the tank and when I restarted the car it still idled roughly. By the time I got home (7 miles later) it was idling VERY roughly. The car is a 1988 Corvette with a cut air lid, no MAF screens, no precats and an AFPR.
I put a fuel pressure gauge on it when I got home and the fuel pressure was 47 with no vacuum and about 39 running. When I blipped the throttle the fuel pressure jumped then slowly dropped. The idle by this time was so rough the car barely ran. I pulled the codes and got a 34. I unplugged the MAF and started the car and got a 33. The software was still indicating a VERY lean condition. I erased the codes and started the car again, now it was super rich and dumping black smoke out the tailpipe. The car would not start and idle with throttle input. I checked the codes again and got a 33 again. I plugged the MAF back in and it still ran terribly, wouldn't idle without throttle input. When I turned it off to get the codes this I got a 36.

Any ideas what would cause this? I thought with the low fuel level maybe I clogged something, but I get good fuel pressure (haven't tested under load yet). I am going to go do some multitester diagnosis for a bit. See ya later. Please feel free to suggest anything. Thanks, Bob

Ed Maher

I'd like to see FP under load before i made a guess myself. Good chance you fried the FP though if you were out driving spiritedly in the mountains with low fuel. The fuel pump is cooled by fuel so when it's low it's dry, and it also works hardest when the FP is high under load. And they canm just get really weak before they finally go all the way such that it might be ok @ idle and revved for a second, but no way under load.
But then again, it could be something dumb like the MAF, lol, you never know.

BobMachus

How about some fuel pump diagnostic tips? Thanks, Bob

Ed Maher

Does your FP fall under load? If yes you have a fuel delivery problem, if no, look elsewhere...

BobMachus

I went over to try the MAF from a friends 86 Corvette. I plugged it in and VIOLA!! my car ran great! All the diagnostics for the MAF from the Haynes, and the Shop manuals did no good diagnosing this. YEAH!!!

Ed Maher

lol, like i said above, could've been fuel, could've been something dumb like the MAF. Glad you're fixed...