[Gmecm] Hard cold starting

Fri Jan 13 15:15:37 UTC 2012

I know what you mean about having a vehicle you can't trust! That's no fun.

When you check the fuel pump circuit, remember though, that the oil pressure 
switch is a backup system, and that the ECM fuel pump relay will maintain 
the fuel pump without the oil pressure switch.

None of my EFI conversions have an oil pressure switch. I have used only the 
ECM controlled relay and never had a problem. My reason is not wanting to 
have extra wiring on the fuel pump circuit that is vulnerable to shorting 
out and shooting the fuel pump fuse. Also I can use the oil pressure port 
for something else (such as a turbo oil supply).

If you're sitting in the truck, and tap the gas pedal after cold-starting it 
can you keep it running?

----- Original Message ----- 
From: "Jared Ryan" <jryan at caminofx.org>
To: "David Allen" <davida1 at hiwaay.net>
Sent: Friday, January 13, 2012 9:05 AM
Subject: Re: [Gmecm] Hard cold starting

>I think what I am going to do is prove out the oil-pressure switch and its 
>wiring, and replace the switch if the wiring is good (switch is cheap, if 
>hard to reach), then explore what difference the Crane camshaft makes.  My 
>stumbling block is that this camshaft is supposed to be meant for 
>fuel-injected engines, and it doesn't idle lumpy, and I haven't read 
>anything online about people replacing the chip after installing this 
>camshaft.  I really don't know, though.  I'm open to any ideas.  I'm just 
>frustrated at having a beautiful vehicle I can't trust to drive anywhere.
>
>
> 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
>>> _______________________________________________
>>> Gmecm mailing list
>>> Gmecm at diy-efi.org
>>> http://lists.diy-efi.org/mailman/listinfo/gmecm
>>>
>>
>
>
> 