Question on Cold Starting

[jon hanson]

At 01:06 21/09/97 GMT, you wrote:
>>>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.
>>
>>Any guess as to the pulse duration at 20 degrees C?
>>
>>Ric Rainbolt
>>
>>
>Nope - try about double the standard idle pulse, for starters
>
>

I have an after market efi system on a 1587 cc 4 cylinder engine
When the ignition is turned on and the temp is below a user specified
temp (60 deg C in my case) all 4 injectors are given a priming squirt
the length of which is dep on another user specified number.
here's the trick part. the no which works out to a pulse length can be
between 0 and 255. When I first got the car, it was pretty cold here
around 0-5 deg C in the morning. I gave it a no of 240, figuring too much
was  better than too little. the car would start after some cranking and 
throttle juggling. One day as an experiment I set the no to 100 and waited
till the next morning (thats the problem with these temp related problems
you do a lot of waiting). Engine fired at the first turn of the key, problem
solved.

to quantify the above
engine capacity is 1587 cc / 4 cylinder
my injectors flow around 21 lbs/hour
a value of 240 gives a 4.7 ms pulse ( the formula is in the owners manual)
a value of 100 gives a 2.2 ms pulse

be careful of the above figures, the system I use pulses
all 4 injectors 4 times for every 720 deg of crank rotation, from 
what I've read most batch fire systems fire all the injectors 2 times
for every 720 deg of crank rotation
so you would have to double the above pulse durations
to 9.4 ms and 4.4 ms respectively

To clarify matters their is also a warm up enrichment table which is active
and reduces as the engine warms up, the above is a totally separate priming
pulse
(a simple form of cranking enrichment).

Regards Jon Hanson.