Too much fuel?

[Chewy1576]

After swapping to a BB throttle body and 16197427 ECM, I have been having a hard time getting a consistent idle in closed loop. In open loop, it seems to run really smooth, but once it goes closed, the idle gets really unstable. The RPM stumbles along with a drop in integrator value. Once the value gets to 124 stall saver kicks in, it revs up, then starts over again. I was watching the live BPW value, and it was getting to the min allowable value so I lowered that a little bit. I attached my current BIN and a log of the stumbling idle.

I had it running somewhat reasonably with the SB throttle body, same injectors/FP, and a 1228747 ECM. Do I need to go back to the SB throttle body or less flow injector/higher FP in the BB throttle body? Shouldn't the BLM adjust when the integrator gets that low to adjust C/L idle fueling? I'm stumped...

[steveo]

fighting closed loop to get idle right is sometimes a losing battle. smaller throttle bodies have superior incoming air velocity at low RPM which can result in more low airflow stability. you might have tipped it over the edge where it no longer "wants" to idle at stoich. smallblocks prefer a slightly richer idle, especially without mpfi due to uneven fuel distribution. you might want to just consider forcing an open loop idle, and allow somewhere around a 14:1 ratio at idle when warm, it'll be way happier.

[Chewy1576]

I did have to back the minimum idle screw all the way out to get it to idle without the IAC closing completely. It also probably doesn't help that I have the BB throttle body on top of a spacer and bolted to an Edelbrock 3704 intake. I got really ambitious and was going to bore out the intake to 2" to match the BB throttle body, until I saw that the passenger side bore was 6" deep and I knew there were water jackets nearby the bores anyway. So I just bolted them on anyway and went with it. Maybe I need to go back to the SB throttle body with the 80 lb/hr injector setup for now until I get the correct intake?

[fastacton]

Are you using an early or late BB throttle body? The second version had drastic changes to the IAC passages, so I'm assuming that the early version might have had some idle issues in certain situations?

[Chewy1576]

Are you using an early or late BB throttle body? The second version had drastic changes to the IAC passages, so I'm assuming that the early version might have had some idle issues in certain situations?

Its the late BB throttle body. I went after this one because of the opened IAC passages.

[Chewy1576]

The SB throttle body is back on the intake with the 80.5 lb/hr injectors and 13 psi of fuel pressure. It runs much more smoothly than it did with the BBC throttle body.