GM ECM injector driver capacity

[Ken Kelly]

Bruce & Brock,
	An earlier post suggested that the ECM uses an LM1949 to
drive the injectors. I just found the LM1949 in a National
handbook. It has some very interesting info in the article.
It states "Fuel injectors can usually be modeled as a 1 ohm
resistor in series with a 2mh inductor, however the value of
the inductor will change depending upon whethter the
solenoid is open or closed.

	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. 

	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.

	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.

		Ken

Bruce Plecan wrote:
> 
> From: Jennifer and Brock Fraser <fraser at forbin.com>
> Subject: Re: GM ECM injector driver capacity
> 
> it would be a good idea to monitor it's temperature rise with 8
> >>injectors, and then with 16. If the driver can handle 16 at reasonable
> >>temperatures, you could mount a larger heat sink or small fan on it to get
> >>through the higher ambient temperatures found in the car.
> 
> Not a problem
> >
> >Bruce, while you are tap dancing, maybe you could hold your thumb on the
> >drivers to see if they are getting hot.  Of course, like Ken says, running
> 8
> >injectors first would be a good baseline.  To reference your wiring
> >question, I'll send you a plug-n-play solution that all you have to do is
> >hook one end to the drivers, and the other end to +12v.  As you mentioned,
> >I'll have to get some of those little contacts to use on the injector
> >terminals.
> 
> Cool, and yes
> >
> >> The idea of putting injectors in series will reduce the load on the ECM,
> >>however you have to make sure that the injector will work in this mode.
> >Since
> >>you only have 12 volts to pulse the injectors, if you put two in series
> >each
> >>will only see 6 volts. Don't know if they will respond quick enough at
> that
> >>level.
> 
> Has anyone built the injector flow bench, and would they be willing to
> actually measure what happens in the above?.
> Cheers
> Bruce