[Gmecm] Hard cold starting

Sun Jan 15 03:17:07 UTC 2012

I have ruled out the oil-pressure switch as the cause.

I did in fact have a bad oil pressure switch.  It was as old as the car (it was used for the choke relay originally, and I used it for the TBI system when I converted it over).  I changed it out, and it started fine - once.  However, I let it sit for several hours, and just tried it a few minutes ago, and it was back to the same behavior.  It's about 45 F outside right now, much colder than the mid-60s when I changed the oil-pressure switch this afternoon.

It catches quickly and runs STRONG, but I can hear the idle slow down gradually, and that is when it dies.  It goes from a gradual idle slow-down 15-30 seconds or so after it catches, to dying.

What is the name of the table in TunerCat that I can modify to increase the delay for taking out the crank enrichment?

On Jan 13, 2012, at 8:58 AM, David Allen wrote:

> 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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> 