Trying to sort out cold start issues..... When zeroing out the iac count does this in essence completely limit the range of air to come in? What I've been doing is keeping it in the 140 range and tailoring it off to zero as it gets warmer. Obviously from what I know I only get a couple of shots at it when it is completely cold from that point on tuning cold start for me has been a shot in the dark.

 

You beat me to it.
I was about to ask if anybody tried to set the IAC to like 10 to start (higher vaccume) then adjust the fuel according to the IAC.
(If you have too much fuel the IAC will go up to compensate).
I have had waaaay to much fuel and the IAC would go up in the 180 range during cold startup(-15c).

 

In your case if you capped it to say 50 would it still go to 180 to compensate for too much fuel???

 

While were on the subject (newbie), Which is wide open? 0 or 160+? Sorry for the dumb question.

 

0'ing out which table/ entry?.

You typically have:
IAC reset
IAC park
Then IAC warm park.

The IAC reset is to seat the IAC, and then retract it at key off, to verify the count. It then goes to theIAC park.

Then when you start the car, it goes from the park position to whatever count will maintain the commanded idle speed.

The warm start is in sort of a new park position, for a warm start.
Since a warm engine doesn't need as much IAC.

 

Thanks for the info Grumpy!!!!

 

Your welcome...
While no one's asked I thought I'd toss some info out there.

If you set all the IAC stuff to 0, then the engine is in effect cranking with a closed butterfly, so cranking maybe slow, and for some combos so slow the engine may crank alotm and really not pump enough air to get any fuel into the cylinders (TBI).

The hot (actually just restart) IAC counts can be just as critical in that if too low allow the motor to about instantly flood, if wrong.

You want *JUST* enough choke AFR for the engine to run at whatever the worst case IAC count might be when cold. TOO LEAN on a cold engine can be a no run, while too rich can run long enough to foul the plugs. Some combos can be trying to get all the aspects of *choke running*, CORRECT.

 

Now that's good info !!! Thanks again!!!

 

FYI, over around 150 counts is the full flow potential for the IAC. Closing it a little on startup and increasing the min air can help the fuel distribution if your using TBI.

Another thing that really has an effect on the startup is how fast the spark advance is brought in. This is in all ECMs/PCMs in some form or another. There is a constant that controls this. If the timing is brought in too slow, it can cause the engine to suddenly fall off, or stall, after it catches.

 

And you might not max it out, until right at the 250 number, it depends on the IAC (pintle)/ mating orfice your talking about..

 

Hey dimented24x7 what do you mean by to slow? Mine does this now where it starts up but falls off but only when cold like the rest say. Is this the "initial spark advance"? if so and I'm at 8 deg. would faster be 7?

 

Those where the numbers I saw that GM gave for the TBI units with the standard style IACs.

 

There is actually a constant that controls how fast the ECM can go from zero timing during crank to running off the timing tables. If it where to instantly go right to the timing in the tables after startup, it would possibly kick back and trash the starter, and generally be rough. Too slow to start towards running off the tables, and you wont have any advance in time and it wants to stall, from what Ive experienced. The start up fueling obviously also has a large effect as well.

Are you using the 7747? I dont remember off hand where the constant for the timing transition is, Id have to go and look. Its something that you probably wont see in the tuner definitions, though.

 

The IAC wont compensate for fueling. It should be tuned the other way around. Set your desired IAC counts, and make any adjustments to the crank fueling if needed.

 

I'm using a 4488, and from what I see in the constants is it is "initial spark advance" or "main spark bias" , I would assume initial?

 

Is this a fuel only setup, or does the ECM have control of the spark as well?

 

fuel only

 

The above wont apply then, since your using a mechanical dist. Just set it up for what youd typically use and concentrate on fueling/IAC.

 

Ok , I'll leave that alone. So as stated above would you go for the IAC then?

 

IAC park counts and crank/initial choke fueling would be the other things that would have an effect on initial startup.

 

[QUOTE]Originally posted by dimented24x7
[B]There is actually a constant that controls how fast the ECM can go from zero timing during crank to running off the timing tables. If it where to instantly go right to the timing in the tables after startup, it would possibly kick back and trash the starter, and generally be rough. Too slow to start towards running off the tables, and you wont have any advance in time and it wants to stall, from what Ive experienced. The start up fueling obviously also has a large effect as well.

I'm using 6e and can't remember seeing any constant that would control how fast/slow timing rolls in. I know the cool comp.spark works very well in adding spark, but if I could control how fast it does it I could eliminate the run and stall syndrome when cold.

 

IIRC, the SA blend is in DRP's. Do a search in the 6e hac for blend.
Might turn up the table. I don't have a 165 hac with me or I would look. Your problem sounds like a s/u fuel decay is too fast or not enough fuel. Not sure what they are called in 6e.

 

thanks for the replies!!!