Open/closed loop Jeckyl/Hyde

[Bruce Plecan]

> Just started the motor and she's idling lean in open loop. 6E code in an
> 87 Vette, 24# SVOs at low to mid 40s PSI, 218/226 510/510 114 LSA cam,
> idling at 700-800 in Park. The only code I've changed was inj constant
> (25.9#), lower fan on, and higher tc lock.
> I went through the service manual idle set procedure today. Got
> everything perfect. Shut it down, restart, idled at 1400, not the idle I
> set.  In open loop, it runs poorly - lean, low vacuum, low idle, IAC wide
> open. Once it hits closed loop, IAC closes completely, vacuum picks up,
> good AFR, good idle.

> What is causing this? I don't know if IAC or lean condition is causing
> all the problems, although IAC would seem to cause the lean condition.
> Why is the IAC wide open in open loop and closed in closed loop? I must
> have to change something in my program, but what?  Commanded idle speed,
> maybe?

Just some points to look at:
That much cam is going to want more air at idle,  when cold is probably
going to want a richer mix.   Depending on driving sytle, you might do
better with the IAC at idle in drive warm, at 0.   The ecm uses the IAC in a
stall saver mode.

Takes tuning tinkerin experimenting to see exactly what your engine wants
Bruce






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