Inconsistant Start Condition

[paramagicmike]

I have read several posts regarding difficult start conditions. I am adding to the list. Small Block Ford 306 w/ 42 lb injectors, mild cam, 70mm tb, MSD distributor, direct coil control, etc

I found a posting about taking required fuel and cranking pulse width down very low, and start with priming pulse. Got a hint of a revolution at 1.3 ms and moved to Cranking pulse. Cranking pulse had the engine fire slightly at 2.0 ms. Brought required fuel up to 12.9 and the vehicle did start without throttle. Car did idle around 1300 - 1500 rpm. Next day, car came close to starting after 3 short attempts of cranking but died. Warm up wizard, ASE, and other assistance measures have been turned down to take varibles out of the troubleshooting. Not concerned about the idle as I can fix this. Problem is the major inconsistant starts. Car did start after running for twenty minutes and cooling down for an hour. Car started pretty easy.

Also, had another megasquirt guy come over to work on primeing pulse width, cranking pulse width and required fuel. He got some slightly different numbers but did get the engine to run. But same problem I had. His numbers (priming pulse width and cranking pulse width did not get the car to start.) Again, all enrichments have been turned off. We would also get an occasional backfire (smoke) through the exhaust. Actually, it was a very loud bang. Any help would be great.....

Mike

[devastator]

The ASE, Cranking pulse, and Warm up Wizard, must all work in conjunction in order for the engine to start and idle at different temps. The Priming Pulse is not supposed to be used to start an engine, but it definitely contributes to the starting conditions. Your inconsistent starts are likely caused by the lack of the enrichments that you turned off. Also, are you using an IAC?

[paramagicmike]

I am using PWM. I did not have any accurate numbers until recently. I found some ford numbers under success stories with PWM. I will plug those numbers in today and see if this helps. I'm sure there will be some benefit. One of the things I noticed is that small-block ford guys have a long cranking pulse widths compared to what I have had limited success with. Both tunes I looked at were around 10 m/s. I am concerned because I had those massive backfires under cranking and believe it was from longer cranking pulsewidths. I understand that all setups are unique and you need to go with what your engine responds to. Just seems like those numbers a a bit large.

[devastator]

Usually too much fuel will cause fouled plugs, not a backfire. Often backfires are the result of unburned fuel in the exhaust that ignites, meaning that there is not enough fuel entering the combustion chamber to start the engine with, but there is enough to accumulate in the exhaust an cause a backfire.

[paramagicmike]

So that could be why I am getting such a loud bang occasionally while attempting to start. That would also explain the Cranking Pulse Width the other small block ford guys are using. Very large numbers compared to mine. All I am doing is attempting to get the car to fire with a lean condition and loading the exhaust with fuel. Cranking the engine for a period of time will eventually get the right mixture in the cylinder and the exhaust and then pops. I am heading out shortly to try some of hose numbers I discovered. Since I have not a much time to tune the idle, the plugs are showing a rich mixture. This again a why I was so concerned about adding more fuel. We will see what happens. Also, when you started your engine for the first time, did you use the warm-up wizard numbers that were already in the program?

[devastator]

So that could be why I am getting such a loud bang occasionally while attempting to start. That would also explain the Cranking Pulse Width the other small block ford guys are using. Very large numbers compared to mine. All I am doing is attempting to get the car to fire with a lean condition and loading the exhaust with fuel. Cranking the engine for a period of time will eventually get the right mixture in the cylinder and the exhaust and then pops.

Sounds about right to me.

Also, when you started your engine for the first time, did you use the warm-up wizard numbers that were already in the program?

Those numbers were so far off on my engine that I had to lean them out a bunch, but I'm running E85 too, so this may not apply to you.

[vinister]

It is worth looking into cranking advance as well, as this has quite a significant impact. Also the cranking AIC PWM is quite important, because obviously the amount of cranking PW is dependent on how much air is getting into the engine. There isn't very much documentation about this setting... how much air should we be letting in during cranking? The same as is required for idle, or more/less? Myself I have a slightly higher air PW than the corresponding idle PW for that clt temp.

[devastator]

Good point Vinister. I have the ignition skip pulses set to 10 so I do not get more than the basic advance during cranking. It usually starts in less than 10 revs. I've also noticed that my engine does not like a ton of air when starting. Just a little more than idle works well for me. I've also seen the engine ire for a second, kick in to the VE table, (way lean at the time), then stall back to the cranking pulses, making starting the engine confusing to say the least.