[Diy_efi] Dead cold rough idle
Lee M. Lemoine
llemoine
Fri Feb 17 20:40:35 UTC 2006
I guess thats also possible.. it seems to be odd that it idles up fine, but
then after the cold start enrich decays off, it starts this problem..
On 2/17/06, Rick McLeod <dunvegan at sbcglobal.net> wrote:
>
> Icing is a good potential, a lot of throttle bodies
> have a pre-heat of some kind, the TPI on GM
> Camaro/Vette 85-92 era had a water line that was sort
> of the bypas hose circuit, many folks (myself
> included) have passed a copper pipe under the Throttle
> Body for summer use, and just move the hose from the
> Body to the pipe and back every fall/spring. That way
> you get the de-icer in the winter and not in summer.
>
> just an idea, my memories of my old VW icing up at
> idle even after engine warmed up, usually forgotten to
> unlock the air diverters for carb intake preheat from
> summer mode, It was a simple solution but extremely
> elegant in function. You may never see frost or icing,
> it may be occuring inside the passages, but will wreak
> havoc with idle if it is occuring.
>
> Good luck!
>
> --- Torbj?rn Forsman <torbjorn.forsman at gengas.nu>
> wrote:
>
> > Hunting at idle might also be caused by wrong
> > control parameters for the
> > idle speed stabilization or too early ignition
> > (then the engine
> > response to a change of the idle air valve will not
> > match the control
> > parameters and the system will oscillate).
> >
> > Idling problems at a cold engine can usually be
> > avoided by a good intake
> > air preheating and, of course, heating of the intake
> > manifold. Some
> > european TBI engines (for example, the 1,6 and 1,8 l
> > engines of VW
> > Golf/Rabbit from about 1988 to 1997, with Bosch
> > Mono-jetronic or
> > Mono-motronic TBI) have an electric PTC heater of
> > about 300 W directly
> > below the TBI unit. This heater is controlled either
> > by a thermostat or
> > by the ECU, so that it is switched on from a cold
> > start and until the
> > coolant temperature has reached about 50-70 ?C
> > (120-160 ?F).
> >
> > Best regards
> >
> > Torbj?rn Forsman
> >
> > Lee M. Lemoine wrote:
> > > 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
> > > <mailto: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
> > <mailto:dingebre at 3dphysics.net>
> > > Work: 801 733-5458
> > >
> > >
> > >
> > >
> > >
> > >
> > _______________________________________________
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> > > Diy_efi at diy-efi.org
> > <mailto:Diy_efi at diy-efi.org>
> > >
> > http://lists.diy-efi.org/mailman/listinfo/diy_efi
> > >
> > >
> > >
> > >
> > >
> > >
> > > --
> > > Sincerely,
> > >
> > > Lee M. Lemoine
> > > http://www.turbochargedsoul.com/
> > <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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--
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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