Hi Jon,
I think you are going the wrong way about the control of injectors.
A better way to trim injector duty cycle is to modify the inputs
the cars ECU gets, ie vary the signal level from the air flow
meter + or - an amount.. Trick the ECU into delivering less fuel.

Regards
Peter Mcalpine
petermca@ozemail.com.au - www.ozemail.com.au/~petermca
mcalpine@gme.net.au - www.gme.net.au
www.wrx.org.au


----- Original Message -----
From: Jon Petty <Phxsys3@AOL.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Wednesday, 19 May 1999 9:56
Subject: Limit fuel injector pulses


> Hi everyone
>
> I want to use a PIC or even a stamp to manipulate fuel injector pulses,
> mainly reduce the pulse width. I really don't want to utilize individual
> injector drivers (for sequential injection systems) that will complicate
the
> project. As you are probably aware sequential systems usually use an
> individual driver for each injector. One side of all the injector has a
> common 12v source to all injectors and the individual drivers (sink)
control
> the ground.
>
> I was wondering if it is possible to modulate the 12v power line which is
> common to all injectors. For example say the PIC measures the previous
> injector pulse at 5 msec and I want the injector to pulse 2.5 msec on its
> next fire. Could I allow the injector to fire normally and cut the power
at
> 2.5 msec (to shut off the injector) and turn power on again in time for
the
> next injector firing? I am not sure what effect the  rise and fall times
of
> the power supply will have on injector firing or operation.
>
> If this is possible, I would just need one power control circuit to trim
4-8
> injectors. I could easily use a PIC to measure the pulse, allow the
initial
> injector firing to happen on schedule and trim each injector by
controlling
> the power source which is common to each injector.
>
> What do you think?
>
> Any comments or suggestions for hardware that could accomplish this?
>
> Thanks in advance
>
> Jon