[Gmecm] Hard cold starting

[David Allen]

Jared, IIRC there is a table in the ECM that determines how long it takes 
for the
cranking-enrichment to be decayed out of the fuel delivery.

I've been working on a Buick engine with a "mild" cam, and it too requires
richer mixture to stay running when cold. I don't have the tuning program in
front of me to look at - but I beleive I doubled the time it takes to remove
the enrichment.

Also the ignition timing curve was VERY sensitive compared to the stock cam.
To idle correctly there is about a 2 degree window between stall out and and
going "zoot-zoot-zoot-zoot" when it idles.

Hope this helps!
David

----- Original Message ----- 
From: "Jared Ryan" <jryan at caminofx.org>
To: "A list for discussing General Motors EFI" <gmecm at diy-efi.org>
Sent: Friday, January 13, 2012 7:40 AM
Subject: [Gmecm] Hard cold starting


>I have tried working on this before but never had any success, nothing that
>made a real difference.
>
> Here is what I have:
>
> 1984 Chevrolet El Camino
> '87-later-style 350 GM long block, NEW in 2005
> Crane 2032 roller camshaft
> Edelbrock Performer TBI intake manifold
> GM throttle body with 55 lb. injectors (IIRC; I have a spec sheet for them
> at home)
> Stock 305 exhaust manifolds
> Painless Wiring TBI wiring harness
>
> It is a relatively tame engine, meant for street reliability in a small
> pickup.  My problem is cold starting.  Here is what happens:
>
> When it is cold outside, and the engine has not yet been run that day, I
> turn the key, crank it, and the engine catches after four or five seconds,
> and goes to a smooth, moderately high idle (1300-1400 IIRC).  Then, after
> a short period of time - yesterday it was about ten seconds - it will
> suddenly stop running.  There is little warning; sometimes it will run
> rough for a second or two, but it is very abrupt.
>
> When I turn the key, it starts back up in a second or two, but it usually
> does it again.  Yesterday I went through three cycles of this before it
> started and stayed running.
>
> What I do not understand is that the car previously had a 305 in it, with
> the exact same setup with the exception of the roller camshaft and
> Edelbrock manifold (used a modified GM TBI manifold), and I never, ever
> had this problem with the 305.  Ever.  It just started up and stayed
> running, smoothly, like a fuel injected engine should.  Same wiring
> harness, same fuel pump, same fuel lines.
>
> This behavior usually does not happen in the late spring and summer
> months.  Whether it happens, and how long it takes before the engine
> quits, seems to be highly dependent on the ambient air temperature.
>
> What I have seen from the ALDL seems sane, especially regarding coolant
> and intake air temperature.
>
> I have tried both a 1228746 ECM with a '90 Caprice 350 chip, and a 1227747
> ECM with a '91 1500 Suburban 350 chip.  I reset the minimum air when
> changing ECMs, but the behavior is the same.
>
> I may have a possible clue.  I tried enriching the open-loop mixture in a
> chip for the 1228746, and I got it so that it would - most of the time -
> stay running when it is cold outside.  However, this was at the expense of
> the exhaust smelling VERY STINKING RICH.  Like, stinging the eyes.  But
> that at least gives me the idea that it is somehow going lean, and that is
> what makes it die.
>
> I looked at the EGR valve yesterday and it looked like it was stuck open,
> so I put a new one in, but there was no change.
>
> Is there something really stupid obvious that I may have overlooked?
> Something, anything, that might make it go lean and stumble and die when
> it is cold?  It seems like, once the combustion chambers warm up a little,
> it is fine, but getting it to that point can take starting it three or
> four times.
>
> What I am wondering is if there is something beyond the ECM programming
> that would allow it to start easily when dead-cold, but then somehow make
> it go lean after a few seconds.
>
> I am very, very frustrated with this.  I love the vehicle but I can't
> trust it to drive it on cold days.  It is not normal behavior for GM TBI,
> and I don't know where to turn.
>
> Once it is warm it runs GREAT.  Smooth idle, even acceleration, 22 mpg gas
> mileage - just a joy to drive.  But that hardly makes up for not being
> able to just start it and GO first thing in the morning!
>
> Jared
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