[Diy_efi] am i destroying my 749 ecm?

[Ludis Langens]

lou trapane wrote:
> 
> I just got my truck out of the garage and need some advice.  I am using
> a 749 sunbird ecm to fire 2 injectors in my GM TBI.

No problem so far...

> first...the GM tbi uses the P&H style injectors corrcet?  I am only
> driving two(of course)injectors-- one from each injector output.  Am I
> overheating or destroying anything?

...you have essentially the same loading as with a P4 ECM driving a
single injector car TBI unit.

> second...i am going to use two tbi's to feed my roots blower so i need
> to drive 4 total--can i just wire 2 injectors to each of the ecm's
> drivers?  I have the parts to build an injector driver board sitting on
> my bench  will i need this?  I read a few places where the 749 can drive
> 4 P&H injectors stock..is this for real?

Oops.  That won't work.  Each injector driver in a P4 can drive *one*
TBI style P&H injector, or two port injection P&H injectors, or eight
high impedance port injectors.  In the OEM hookup where a '749 is
driving 4 P&H injectors, the P&H injectors each take half the current of
your TBI injectors.

You will need to build your injector driver board.

> third...what do the injector jumpers on the 749 do for me?  it shows in
> the 749 pinout to have them connected together.   I currently have them
> connected togther(the proper wires together of course) and the whole
> thing seems to run just fine.

Check the ECM schematic on my web pages.  In P&H mode, the jumpers allow
the ECM's current sensing circuit to watch the injector current.  In
saturated mode, the jumpers bypass the current sensing resistor.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/
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