Question on Cold Starting

[Clare Snyder]

>
>I'm trying to tune a custom EFI system that I've developed and I'm having
>trouble with the cold start.  By cold I mean room temp, which in my garage
>lately has been about 70-80 F.   I've tried many settings from moderately
>rich to "pig" rich and nothing at all happens until I squirt some Carb
>cleaner into the manifold.  Once I do that, the engine will hit and then may
>start (or may not).  One or two shots of Carb cleaner more and it starts and
>runs (at which point my warm up cycle takes over and seems to work OK).
>
>More info:
>  8 cylinders with port injection
>  Injectors well matched to engine output
>  No cold start injector
>  250 RPM cranking speed nominal
>  Good spark, new plugs
>  Hot re-starts work OK
>
>Does anyone have any info on good "start" algorithms?  One that I have not
>tried yet is a rapidly decaying very rich to a little rich scenario.  Say,
>2x to 3x the normal amount of fuel for the first few revs and then back off
>to 125% over a 20 rev range.
>
>What do "factory" systems do?
>
>Ric Rainbolt
>ricrain at airmail.net
>
>
when cold, first ignition pulse triggers a "prime " pulse on all injectors.
This is a common setup, used by GM and others. Easy enough to implement, I
would think, even as an addon.just a oneshot triggered by the ignition
pulse, and not retriggerable.