[Diy_efi] Dead cold rough idle

[Lee M. Lemoine]

Usually when the engines hunting like that your at the edge of a fuel map...
meaning that either your 500 rpm table is set too rich, so the extra fuel
makes the engine rev a slight bit... but the 1000 rpm table may be too lean,
so it falls back again...  (rinse, repeat, etc) and viola -- a rough idle.
The other things that I've seen related to this would be the air intake temp
compensation (too much / too little) or even coolant temp compensation,
although you say it seems to do that even after warmup.

Most EFI systems use a 'cold start enrich' map, which lasts the first 30
seconds or so, and fades out gradually.  What this means on a cold engine is
an increased amount of fuel -- causing it to start easier and (in your case)
idle smoother..  my guess is that whatever range your trucks idling in'...
the fuel maps too lean ...

Related to that ...  When's the last time you changed the fuel filter /
how's your rail pressure?  Maybe your fuel pump is also weak at colder
temps?  (just a thought!)

--Lee


On 2/17/06, David M. Ingebretsen <dingebre at 3dphysics.net> wrote:
>
>     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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>


--
Sincerely,

Lee M. Lemoine
http://www.turbochargedsoul.com/
'06 Subaru Legacy GT Limited - 250/250 AWD 5EAT
'93 Chevy Cavalier Z24 Convertible - 300/330 FWD 5MT (Mclaren Turbo!)
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