stalls after cold start

[ChevelleFan]

Wondering if someone can help me out here.. my car runs really well 99% of the time. However, on a true cold-start (first of the day), it starts, RPMs probably hit 1500-1700, starts to taper down, then dies. Re-starting (without power-cycling) and the engine will catch itself and then idle fine. Every now and then it will die after the 2nd restart, but usually it stays running. Log and MSQ included in the ZIP file.

Thanks in advance..

-Dave

[Matt Cramer]

That's a lot of timing at idle - you might want to try less timing and more throttle opening at idle. Running more than ~18 degrees at idle tends to make for idle stability issues.

[ChevelleFan]

Thanks Matt! That advice worked really well. Added +1 turn to throttle opening screw, it started and stayed running fine. Idle seemed a little too high, backed it off 1/2 turn, so net +1/2 added, dropped timing in idle area down to 18* and the combo of the two made a nice improvement in idle + off-idle.

-Dave

[anesthes]

That's a lot of timing at idle - you might want to try less timing and more throttle opening at idle. Running more than ~18 degrees at idle tends to make for idle stability issues.

I'm confused by this.

I'm running about 24 degrees at idle just to keep the car (Formula) stable.

On my C4, the stock PCM runs 36-37 degrees at idle, and that has a much smaller cam than the 412" on my Formula.

-- Joe

[Matt Cramer]

There used to be a meme going around that 5.0 Mustangs required 50 degrees of timing at idle, apparently based on some sort of stock map. And we had a LOT of Mustang owners complaining about unstable idle. When we released the MSPNP, which had a map that used far less idle timing, more people copied our map and these complaints about unstable idle dried up in a hurry.

[Blown88GT]

There used to be a meme going around that 5.0 Mustangs required 50 degrees of timing at idle, apparently based on some sort of stock map. And we had a LOT of Mustang owners complaining about unstable idle. When we released the MSPNP, which had a map that used far less idle timing, more people copied our map and these complaints about unstable idle dried up in a hurry.

Stock map is about 28 deg. Yours is 16 deg.
http://www.efidynotuning.com/saftot.htm
http://www.efidynotuning.com/mbt.htm

[anesthes]

There used to be a meme going around that 5.0 Mustangs required 50 degrees of timing at idle, apparently based on some sort of stock map. And we had a LOT of Mustang owners complaining about unstable idle. When we released the MSPNP, which had a map that used far less idle timing, more people copied our map and these complaints about unstable idle dried up in a hurry.

Any guidelines you use based on cam size ?

I've been trying to dial in a tune on my 412" SBC and I have not had the best of luck. If I reduce the timing below 24-22 degrees I have to open the throttle blades quite a bit to maintain idle.

-- Joe

[Matt Cramer]

Greg Bannish put it best: Your goal for idle tuning is to balance engine torque against friction to hold the engine speed constant. An engine with a wild cam will need more help making enough torque to overcome friction, in the form of either air or timing. I've found more air is often a bit more stable than more timing.