[Diy_efi] Dead cold rough idle

David M. Ingebretsen dingebre
Fri Feb 17 17:08:56 UTC 2006


  
Hello all. Been awhile since I've lurked here.
 
Setup: 1990 Jeep Wrangler, 4.2 liter inline 6, Originally a Howell GM TBI
conversion with 1227747 ECM, now happily modified and tuned.
 
I've searched the archives, web, and FTP site and didn't find anything which
helped.
 
The problem is this. When cold, (even using the Howell supplied bin and
their "cold" bin) at or near 0 C, the Jeep starts great, starts idling fine
but after some 15 to 20 seconds at idle, the RPM's drop and it begins to
idle very rough. When I drop it into gear (was manual, now Chevy 700R4 auto,
yes I added a pk/ntrl switch and have verified its operation with WinALDL,
and I am using the ECM to control TCC lockup) and go, it runs fine. Smooth
engine speed and running. But soon after I stop (2 to 3 seconds) it starts
to idle rough, sputter, cough, on occasion die. If I poke the accelerator it
comes back and when I start, no problem. When fully warm, no problem. When I
start it at about 30 to 50 C, no problem. This was the same with the manual.
 
Question is what -exactly- controls the cold open loop -idle- AFR? I've had
no luck changing the O/L AFR table except to make it run crappy before it
goes into closed loop. I've adjusted the closed loop temp threshold, cold
and warm choke timer, choke table, cold AFR v. MAP, time out decay mult. V.
Cool. O/L idle AFR enable time delay, O/L idle AFR time delay, closed loop
timer warm threshold and timer. I've looked at the Accel Pump v. Coolant but
that doesn't seem to be a problem because I can hit the throttle and it
snaps right in. I've searched the AZDZ hack to see if I could glean anything
 but didn't find anything useful.
 
Like I said, it is fine when it starts warmish, but when it is dead cold it
struggles. So, my thoughts turn to the choke table, but I'm not sure.
 
Any ideas?
 
Thanks all.
 
David M. Ingebretsen M.S., M.E.
Collision Forensics & Engineering, Inc.
2469 East Fort Union Boulevard, Suite #114
Salt Lake City, UT 84121
 
dingebre at 3dphysics.net
Work: 801 733-5458
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