Trying to get pre-crank injector pulses

[kilohertz]

Hi guys,

I read somewhere over a month ago that someone had managed to get pre crank injector pulses but I can't find the thread.

Could someone please help me with the code or method to get a few pre crank pulses on the TBI ECM 1227747?

Thank you.

[kilohertz]

A little more research... I found it looks like the pre-crank pulses were done on the second gen ECMs, '93-'95??

Does anyone have an ECM that has the pre crank pulses, that could share a BIN code so I could try to find it and implement it in the 1227747?

thanks!

[Six_Shooter]

You mean like a Prime pulse? All GM ECMs do that AFAIK.

[kilohertz]

You mean like a Prime pulse? All GM ECMs do that AFAIK.

Exactly! Mine doesn't, and I have tried 3 different BCCs.

My injectors won't pulse until it's cranking, and with the convoluted intake path of the Flathead, I would like to have some fuel sitting on the butterflies ready to get sucked in.

Thanks!

[In-Tech]

The '7747 is pretty archaic and I don't think there is a prime pulse, from memory. If your injector/cu in constant is correct(very critical)...then all you should have to tailor is IAC counts during crank. I realize this is a bit vague. Bottom line is it will take a bit of work since you are starting from scratch basically. It seems like you are well on your way.

[kilohertz]

The '7747 is pretty archaic

Ha! But miles ahead of a Holley 94 carb.

If your injector/cu in constant is correct(very critical)...then all you should have to tailor is IAC counts during crank. I realize this is a bit vague. Bottom line is it will take a bit of work since you are starting from scratch basically. It seems like you are well on your way.

Thanks Carl. Yes I have moved from 2.8L injectors to 4.3L and the math comes out to BPW of 126 for the 3.9L Flathead with BSFC of .65 and 100HP. I have played with the IAC park position but didn't realize it was that important...I will continue to fine tune it. Appreciate the info.

Cheers