[Gmecm] Hard cold starting

[Jared Ryan]

It just did. :-)


On Jan 13, 2012, at 9:04 AM, Butler, Jim (NSN - US/Arlington Heights) wrote:

> I'm sure it's occurred to you that you can just jumper the fuel pump
> test connection to the battery easily, to test this hypothesis that the
> oil pressure switch may be open/opening.
> 
> :o)
> 
> Jim
> 
> -----Original Message-----
> From: gmecm-bounces at diy-efi.org [mailto:gmecm-bounces at diy-efi.org] On
> Behalf Of ext Jared Ryan
> Sent: Friday, January 13, 2012 8:58 AM
> To: A list for discussing General Motors EFI
> Subject: Re: [Gmecm] Hard cold starting
> 
> I did not realize that the ECM might cycle the relay on and off during
> the start-up process.  Now that I think of it, with a cold engine I'm
> pretty sure I do NOT hear the fuel pump after the engine stalls.  In
> fact, I noticed that a while back, but did not know what to make of it!
> 
> The oil is fresh synthetic 10W-30 with a good filter but switches can go
> bad (and wire connections can go bad as well).  Oil pressure is very
> good at the gauge once the engine is running.  It is relatively cold
> here in Houston - 40s daytime - so the oil is going to be relatively
> thick, and the switch is at the very top of the block.
> 
> Your theory makes sense and at least gives an avenue to look at that I
> haven't covered adequately.  Thank you.
> 
> Unfortunately, the shape of the Performer TBI manifold and its proximity
> to the throttle/cruise control bracket prevents me from putting the tap
> for my fuel pressure gauge right behind the throttle body.  I am not
> sure if it would be meaningful to put it after the filter, which is the
> other place with threaded fittings I could put it.
> 
> 
> On Jan 13, 2012, at 8:41 AM, Aaron wrote:
> 
>> OIL Pressure.
>> 
>> The first thing that came to my mind was not EFI at all.
>> I'm not sure how your fuel pump is wired, but IIRC GM liked to use the
> ECU
>> to fire the fuel pump relay for a short time when the key was turned
> on.
>> Then turn it back on during starting. The ECU would keep the fuel pump
> relay
>> on for another short time after cranking. This second delay was
> waiting for
>> the oil pressure to build up enough for the oil pressure switch to
> hold the
>> fuel pump relay on. 
>> To me it sounds like the fuel pump relay is NOT getting held on by oil
>> pressure from the oil pressure switch. Thick cold oil or a filter with
> too
>> much material to pump through or a weak oil pump, all could cause this
> type
>> of cold start issue.
>> When you added more fuel, stinking rich, I think you covered up the
> fact the
>> fuel pump shut off, by running on leftover fuel in the runners and
>> combustion chamber.
>> 
>> I quick check would be a fuel pressure gauge installed and watched
> during
>> startup or a voltage check on the oil pressure switch to fuel pump
> relay
>> circuit.
>> 
>> -----Original Message-----
>> From: gmecm-bounces at diy-efi.org [mailto:gmecm-bounces at diy-efi.org] On
> Behalf
>> Of Jared Ryan
>> Sent: Friday, January 13, 2012 8:41 AM
>> To: A list for discussing General Motors EFI
>> 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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