FFCam1991

iTrader: (4)

Just swapped a 350 into my 91 Firebird, so we're talking speed density TPI here. The exhaust seems to leak pretty bad from a few places...I can here a very distinct and raspy "pap pap pap" coming from the engine bay (I hope it's just an exhaust leak).

What kind of issues can an exhaust leak cause for a new motor? My BLM's are at 96 at idle so it's obviously running super rich. Will leaks cause an 02 sensor to read rich or lean? Could that noise be something more serious? I dropped my fuel pressure because I know my fuel pressure gauge is faulty, but that made no difference.

Yesterday I took it out for a spin and it performed quite well, but I didn't have a data logger hooked up. Today I was letting it idle, and I tapped the throttle twice, knock count jumped up to 5 and the engine died.

This is confusing the hell out of me. The first start up, it held 21 inches of vacuum. Now I'm lucky if I get 15.

I guess it all comes back to fixing that exhaust leak first. Is it safe to use some seafoam to reveal where the worst of the leaks are?

Thanks for any help.

FFCam1991

iTrader: (4)

Couple thoughts,

My FPR (stock diaphragm and spring, new adjustable cap) leaks vacuum slowly when testing it with a vacuum pump. At the upper end (15 to 20 inches) it leaks about an inch of vacuum every 2 seconds, this interval slows down to about 3-4 seconds per inch as the vacuum drops. Is this normal, or are the diaphragms supposed to hold totally steady vacuum? I'm thinking this might be a possible cause of the rich condition. I can smell fuel in the line, but it's nothing like my old set up, where fuel would fly all over the place when you removed the vac line.

Another thought, TunerPro shows no changing value for my MAT sensor. I don't know how much the MAT affects fuel delivery, but it stays at a constant 16 degrees C. I'm thinking this might more of a TunerPro issue (bad .ADS to .ADX conversion or similar) because I'm not getting any DTC's.

Finally, could an overly rich mixture coupled with an exhaust leak cause combustion in the headers that translates to a knock being sensed? Just throwing out ideas.

FFCam1991

iTrader: (4)

Tried the Seafoam thing, I did not see any plumes of white exhaust coming from anywhere other than the tips. New ADX file resulted in the MAT sensor slowly increasing in temperature, which I understand is acceptable. My BLM's are still bottomed out at 96, knock counts go way up when I tap the throttle (27 after a few blips.) The car sounded like it was going to die after it hit closed loop, but regained a consistent idle of 625-675 RPM. Vacuum is about 17 inches.

I'm guessing that the car died because the spiking knock count pulled a bunch of timing. Maybe that, coupled with the extremely rich fuel mixture, caused the motor to stop. I still don't know how the low BLM and high knock are related (if at all), maybe super rich exhaust can still combust and trigger the knock sensor without a serious leak?

Injectors ohmed out at 16.7 - 17.3 hot.

I REALLY need some input!