Open/closed loop Jeckyl/Hyde

[Marteney, Steven J.]

Keep in mind what Bruce said, the IAC can act as a stall saver.  If the
engine is really lean it will miss and not make much power to even idle.
IAC acts as a throttle change just to keep it from dying.  Friend had a 94
Jimmy getting bad mileage and no power.  Went to my friend's house and he
had the intake tube of it.  The thing was sucking air like you wouldn't
believe.  Timing was about base -10 to -15deg!!!  Set timing, engine got
real quiet.  The IAC was compensating for bad engine conditions.  Noy saying
this is it, just the only experience I have.

HTH, Steve

-----Original Message-----
From: akallotte at juno.com [mailto:akallotte at juno.com]
Sent: Friday, March 23, 2001 12:13 PM
To: gmecm at diy-efi.org
Subject: Re: Open/closed loop Jeckyl/Hyde


I set the fp by applying 10" of vacuum with pump.  Will recheck with car
in open and closed loop though.  I have thought about changing the inj
constant, but I'm wondering if the IAC being wide open and killing 4" of
vacuum is causing the lean condition.  Or maybe, the inj constant is
right on, but the 6E fuel tables can't feed the engine at idle.  !!But I
don't want to mess with all that until I know why the IAC is wide open in
open loop.!!  I think it's closed in closed loop because the ECM wants a
lower idle than I have set, but it runs great in closed loop and the IAC
isn't stealing any of my vacuum.  God, I can't imagine this on a MAP car.

On Fri, 23 Mar 2001 10:16:35 -0500 "Marteney, Steven J."
<smarteney at xlvision.com> writes:
> I'm not smart enough to figure out what your injector size REALLY is
(SVO rated at different pressure than GM, etc.) but I have two things.
> 
> 1) Is the fuel pressure quoted basically as measured at idle with
vacuum line attached?  If not, if you set it with vacuum line
disconnected, then pressure at idle is actually high 30's probably.
> 
> 2) If it truly is lean at idle in open-loop mode, start setting your
injector constant to a lower numbers.  This makes the computer think you
have smaller injectors and when it calculates the fuel mix it will
deliver more fuel.  When it goes closed loop, the O2 sense is in control
and will correct if necessary.
> 
> Don't know much about IAC stuff, but lowering the constant WILL richen
the car up at idle.
> 
> Steve (89 F-body 350 similar cam)

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