TBI not getting enough fuel at MAP above 85Kpa

[JF in MI]

Hello all. I'm trying to figure out what I'm doing wrong with a GM TBI system I built. 747 ECM, TunerCat $42. Seems like anything above around 85 Kpa (about 4-5"Hg and lower) under load I'm running out of fuel. I have AFR vs MAP to zero in that range, have gone down to 13/1 AFR vs temp through whole range and max open loop AFR to 13. Also I have it always running in O.L. so it never gets to C.L.
Once the MAP gets below that the engine takes off. Running 12.5 PSI pressure. Any ideas where I should be looking? Thanks.

[dave w]

Maybe increase BPW, but that's a global setting which makes all RPM / KPA's richer.

Maybe post a data log? Maybe post the BLM History?

16959

dave w

[1project2many]

Hi,


Running 12.5 PSI pressure. Any ideas where I should be looking?

This is confirmed while you are at high MAP and the engine seems to be starving for fuel?
Have you confirmed lean operation on O2 sensor or with other instrumentation or method?
Check excessively advanced timing / spark knock present?

[JF in MI]

Maybe increase BPW, but that's a global setting which makes all RPM / KPA's richer.

Maybe post a data log? Maybe post the BLM History?

16959

dave w

OK, here we go; (and this is a bit embarrassing on my part). I went with new injectors on this highly modified project. I took the numbers off the old existing throttle body I was replacing but they were nearly impossible to read. The new injectors were 55lbs/hr but as it turns out the old ones were somewhat higher. I started thinking about what Dave W said and went back and recalculated the BPW and found it was all wrong and probably not even right for the old injectors (I didn't write the original data). It was at 130 and should have been 145. Corrected that and also increased the main fuel table percentages in the upper MAP/lower RPM range and lowered the AFR throughout the temperature range (it may now be a little too rich during warmup but that's easy to correct later). Runs a thousand percent better with only an occasional minor bog at high MAP while first getting the car rolling from a stop. Still working on that but am headed in the right direction. I might add that this is an EFI conversion of an old mechanical Rochester fuel injection and the original throttle plate was too big making it way too sensitive at "tip in" so I made a new throttle bore and plate reducing the size from 3" to 2.2". Much more controllable now.
1696116960

[JF in MI]

Just tested the last chip and it runs like a dream at operating temperature. Just too rich during warmup but I should be able to adjust that out.