[Gmecm] Cold start with 1228746

Tue Nov 30 03:14:50 UTC 2010

Jared, it sounds like as the engine warms up it leans out too?quickly and dies, 
or like you suggest the IAC is closing too quickly and killing the engine. I 
have similar problems with my '89 firebird L03 that I have converted to E85. 
Mine doesnt die, but?as it warms up from a cold start it leans out a little too 
much until it gets?through a certain temp range. Since E85 is a little 
tempermental in cold weather I usually let the engine warm up a bit before I 
drive anyhow. There are 2 tables in TunerproRT for the 61 definition file that 
address open loop AFR's vs. engine temp and open loop AFR vs. engine load. I've 
been too lazy to make changes to my tune in?a while and like your problem?mine 
is only in cooler ambient temps so in the summer I don't have this issue. 
Anyhow, I am unfamiliar with tunercat, but if you download TunerproRT and the 
61v3 definition file you can find these tables and alter them. They are 
additional tables separate from the base ve tables and the crank AFR tables. 
There?are also IAC steps vs. engine temp and choke tables. In open loop your BLM 
and INT will remain at 128. The BLM and INT only go active in closed loop and 
they are based on o2 sensor feedback to keep the AFR at the desired level. You 
need to do some driving and log your BLM and INT in closed loop and make changes 
to the base VE tables to keep them close to 128. Your car may perform well 
as-is, but once the ecm goes into closed loop it's going to alter the fuel curve 
to maintain the proper AFR and therefore you may not realize how far off your VE 
tables actually are. Since you have a slightly more efficient intake and a 
better camshaft, the VE tables will need to be optimized to your particular 
engine combo. I too, haven't made many changes to my ve table and I average 
around 17 mpg with E85, but if I look and my BLM and INT in closed loop they are 
all over the place, but since the computer is continuously monitoring the actual 
AFR and making changes the car performs just fine. As a matter of fact, the car 
runs quite remarkable given the relatively poor tune I am running. As far as the 
AIR pump goes,it technically does not affect the driveability of the vehicle at 
all. The AIR pump is meant to lower emmissions levels at cold startup by using 
fresh air pumped into the exhaust upstream of the catalytic converter. This is 
there the post-converter o2 sensor comes into play on many obd2 vehicles. Other 
than commanding the AIR diverter solenoid on under the proper circumstances, the 
ecm we are using has no other connection to the AIR pump. I eliminated the AIR 
pump as well as the EGR valve long before converting this vehicle to E85 with no 
affects on driveability at all. Although, you can utilize the EGR valve to 
increase fuel economy under cruise conditions, I simply eliminate them just to 
get rid of some of that unnecessary junk under the hood. I hope this info helps, 
and update us if you resolve your problem. BTW my car is a daily driver that I 
use to commute 50 miles to work everyday (yes that is injust 1 direction), so I 
have a LOT of miles of tuning this?particular ECM?under my belt now.

?? Phil

----- Original Message ----
From: Jared Ryan <jryan at caminofx.org>
To: A list for discussing General Motors EFI <gmecm at diy-efi.org>
Sent: Mon, November 29, 2010 3:03:02 PM
Subject: [Gmecm] Cold start with 1228746

I have a Chevy El Camino with a relatively new (not rebuilt) 350 long block, 
Edelbrock Performer TBI intake manifold, stock exhaust manifolds, and Crane 2032 
roller camshaft.

I have been using a 1228746 ECM with an ANLU .bin from an '89 or '90 9C1 cop 
car.? I do not have an air pump but I do have the IAT sender in the air cleaner, 
and it is hooked up and gives a sane reading on the scantool, as does the sender 
in the thermostat housing.

In summer, the engine catches quickly and runs fine.? I haven't put forth much 
effort to really tune it because it drives fine and gets between 19 and 22 mpg 
on the highway (with 3.23:1 rear axle and TH-200-4R overdrive).

Once the temperature goes below about 80-85 F, the following starts happening:

Dead cold, the engine catches relatively quickly, and has a strong fast idle.? 
After about 10-40 seconds (seems to happen faster if it is colder outside), it 
will sound like it's slowing down gradually, then abruptly quit.? I crank it 
again, it fires quickly, and either it will keep running or the same thing 
happens.? I go through more cycles of this if it is colder; it is definitely 
temperature-dependent.

What little logging I have done actually showed values close to 128 at idle 
conditions, so I am not sure what is happening.? Previously, I have tried 
changing the open-loop and start AFR values in the chip, but nothing seemed to 
make a difference.

I have never tried a 1227747 ECM in this car; I have one on the way and I am 
tempted to try a .bin for a truck 350, just to see if it acts any different.

I am not sure what to be looking for.? It's very odd that it catches and runs 
very strong, then abruptly quits.? Then when I crank it again, it catches and 
runs fine (though it may quit again).? Once it has gone through this, it runs 
fine the rest of the day, and warm starts are never a problem.? It is only 
dead-cold starts that give me fits.

Based on how it begins to slow down then dies, it seems to me that perhaps the 
IAC needle is being moved from its starting position.? I don't see a way in 
TunerCat to adjust the rate at which this happens, or perhaps I don't understand 
what I'm looking at.

I never have gotten to the bottom of this, because I primarily drive my Civic 
when it gets colder, and it makes me lose interest in the El Camino.? I'd like 
to fix this, though.
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