Open/closed loop Jeckyl/Hyde

[Marteney, Steven J.]

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)

-----Original Message-----
From: akallotte at juno.com [mailto:akallotte at juno.com]
Sent: Thursday, March 22, 2001 6:33 PM
To: gmecm at diy-efi.org
Subject: Open/closed loop Jeckyl/Hyde


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?
 
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