No idle closed loop 7427 $0D

[jameslleary]

Comp 12-388-4
Surging idle, constantly low BLM's....always 118 or below.
I am still having some issues every now and then, vac in drive, per the data dash, is 15"
But comp swears up and down its not the cam.

[EagleMark]

I'd like to see both the cam cards if you can?

A vacuum gauge, mechanical! Is also a useful tool to look for shake in reading. Won't find it in a log... is vacuum steady at idle? No shake in reading? Accelerate and differences should be smooth, no shake.

There was or still is a 290 HP 350 Chevy engine that just sucked for idle and by specs should not been that bad. There's always a degree issue when installing a cam, or at least check and see how far it's off? Push the cam specs to .224 duration @ .050 and this degree is more crucial with idle!

Or who adjusted the rockers?

15" of vacuum is easily tunable if it's a steady vacuum. But 15" of vacuum could be 17 or 13 depending on elevation.

[96lt4c4]

I'd like to see both the cam cards if you can?

A vacuum gauge, mechanical! Is also a useful tool to look for shake in reading. Won't find it in a log... is vacuum steady at idle? No shake in reading? Accelerate and differences should be smooth, no shake.

There was or still is a 290 HP 350 Chevy engine that just sucked for idle and by specs should not been that bad. There's always a degree issue when installing a cam, or at least check and see how far it's off? Push the cam specs to .224 duration @ .050 and this degree is more crucial with idle!

Or who adjusted the rockers?

15" of vacuum is easily tunable if it's a steady vacuum. But 15" of vacuum could be 17 or 13 depending on elevation.

I am working on getting the cam card, I did not build this motor, it was built by a machine shop. As far as adjusting the rockers, I always 1/2 to 3/4 turn past zero lash.

I have a mechanical vaccum gauge, so I will stick it on the truck next time he brings it by. I am also going to lower the idle speed and raise the timing at idle to see if it helps. If everything else comes out OK.

[woody80z28]

I turned closed loop idle off with my built 350 running $0D. For some reason while sitting idling it would cut the BLM all the way down to 90 and stall. You could see my wideband going way lean as it was cutting the BLM but it continued to lean it out anyway. Open loop idle has been fine and the wideband shows the a/f is good.

[EagleMark]

I'd be interested in seeing your cam card too! I was watching this happen here to in last log but not convinced it is the cam yet, I think there are other issues.

What your describing is to much cam for EFI CL Idle, either duration or overlap and your getting reversion/EGR at idle. there's a point where you can't raise idle, advance timing and lean fuel enough to get good exhaust to O2 sensor. The Narrow Band O2 sensor is lieing, or more acuratly being lied to. When that happens Open Loop Idle is the answer! As you found.