bypassing GM TBI injector pulse from distributor

[marc92040]

I need to bypass the injector pulse from the EFI style HEI distributor on a GM TBI system and still have the system function. would a crank trigger be the way to go, or is there a better way???

 

[pulsewidth]

If memory serves me, the HEI module takes a VR AC waveform and converts it into a REF logic pulse. The REF pulse goes to the ECU. The ECU sends back an EST waveform with dwell start on the rising edge and spark (module trigger) on the falling edge.

I guess if you created a one-tooth-per-cylinder crank trigger wheel and mounted a VR sensor so that the tooth was in the sensor when the crank was close to TDC, you could then run a shielded pair up to the HEI module's VR input. You would need to match the polarity of your new signal to the stock HEI polarity. Connect the shield to ground at the HEI module.

When you go away from the VR sensor in the distributor it is harder to physically correlate actual timing with ECU timing because you can't just turn the distributor till they agree. You may have to provide some adjustment on the VR pickup at the crank.

Good Luck

 

[Andy330hp]

What are you trying to accomplish? Explain the situation