'749 questions

[Shannen Durphey]

EST is ecm output to module.  This is the ecm generated spark signal.

REF is the square wave input to the ecm from the module.  It's an RPM
signal.

Bypass allows the ecm to toggle the module between using and ignoring
EST.  If there is no voltage on Bypass, the module will fire the coil
based on the pickup coil pulses.  This is also the line to disconnect
to set base timing on a real engine.

Crank input is REF, no other needed, signal provided by the module in
both dizzy and DIS systems.

VSS inputs... The VSS has 2 output wires.  It's an a/c signal, the ecm
is connected to both wires.  Any signal buffering is internal to the
ecm.

Be sure to connect the REF LOW (black w/red tracer) between the module
and ecm.
Shannen

Bill Shaw wrote:
> 
> I'm hooking up my '749 on the bench using the stim board from the recent efi332
> list buy.  I have most of it hooked up OK,  but have a few  questions:
> 
> 1)  EST (C8) - is that an input to the ECU with the timing pulses?  2 per rev?
> 
> 2) Reference (D8) - ground?
> 
> 3)  BY-PASS (C7) - what's that?
> 
> 4)  I don't see a crank input - not used on the '749?
> 
> 5)  I see 2 VSS inputs - is that a differential signal? 5V or 12V?
> 
> I think I'm about ready  to power it up and start some ALDL communications.
> With any luck I'll be firing injectors soon!
> 
> Thanks,
> 
> Bill
> 
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