GM ECM injector driver capacity

[Sandy]

>	More importantly the Darlington driver transistor should
>have a 0.1 ohm resistor from the emitter to ground. It
>actually uses this resistor to sense the peak current, and
>decide when to go to the hold current. The value of this
>resistor needs to be changed based on the number of
>injectors if you want to keep the same peak and hold
>currents to each injector. Basically whatever value the
>emitter resistor is for 8 injectors should be cut in half
>for 16 injectors. This really means you should get a
>resistor exactly like it and put it in parallel. If you
>don't do this the peak current output from the ECM will be
>the same with 16 injectors as with 8 injectors, because the
>unit regulates peak current based on the emitter resistor. I
>don't know if the stock peak current will reliably pull the
>16 injectors open. With 16 injectors each should see 1/2 the
>peak current they would see if you only had eight, and one
>half the hold current. 

This was the point that I was making, you will not be able to drive all
them injectors with the driver. If they are in series, you need more
voltage, in parallel need more current, simple. Now expecting a single
transistor to sustain all that current is going to be a probem with a stock
mounted transistor, look at the lm1949 sheet, you will, I think the Tip121
or suggested transistor is rated at 6 or 8 amps. Hmm, 'not in my store you
don't' (from an old van halen video)... 

>	The IC actually uses 385MV accross the resistor for Peak
>current and 94mv for hold current. For the given schematic
>with a 0.1ohm emitter resistor, the total peak current
>should be 3.85 amps, and the hold current would be .94 amps.
>This would be independent of the number of injectors. Each
>injector would see 1/16th of this value instead of 1/8th.

Remember that the circuits are designed to fire one injector, the wattage
capability of the .1 ohm is set for 1 injector, same for the zener, same
for the traces on the PCB. Again, if using the LM1949 more then likely will
have the time out function too, so if you are trying to run even 2
injectors, it will still be limited to .94 amps after the tko is hit.

>
>	There is also a recommended 33volt 5watt zener that absorbs
>the voltage spike generated on solenoid release. This could
>be doubled to ensure protection from the extra solenoids.
>This leaves you with the question - can the driver take the
>additional current.

Likely no, (Sales pitch comming) Just get in on the Injector/Ignition
driver board buy on the EFI332 list, any you can drive that with the stock
ECU's output and run a bunch of injectors off of that. You could even
parallel them, as you have the ability to remove/change the current
limiting functions and behaviour. You could even make a peak and hold
injector system with a 24volt supply and saturated if you were so inclined ;-)

Sandy