I'm planning on converting my '88 back to EFI (speed density), I'm trying to figure out how to splice my MSD ProBillet distributor (w/advance locked out) into the factory harness.

I've scanned in the wiring diagram from my Chilton's manual....

It looks like I can just splice the mag pickup from my dist. in place of the factory pickup, ahead of the ESC module.

I was wondering exactly how the ESC works, and if I can just cut the whole thing out and use my 6AL and HVC coil without having problems with the ECM...


I'm going to make a custom chip to deal with the lack of emissions,A/C, etc. So I can work around a lot of things.

If the advance is in the ECM then I SHOULD be able to 86 the ESC, right?

The overall diagram:
http://albums.photopoint.com/j/ViewP...435&p=28658493


The ECM:
http://albums.photopoint.com/j/View?...nce=0&res=high

The ESC:
http://albums.photopoint.com/j/View?...nce=0&res=high

Also, if I wire my pickup coil in, what wire goes to the PURPLE, and what wire goes to the GREEN on my MSD harness (P or N, yellow underline)?

Is it as obvious as P-Positive, N-Negative?

Thanks,

John

 

John, here's how the GM system works:

The ESC module in the distributor buffers (amplifies) the signal generated by the magnetic pickup coil to create a signal, which pulses 4 times per revolution of the engine. This buffered signal is sent to the ECM over the purple / wht (+) and blk / red (-) dist reference wires. The ECM takes this signal and varies its delay, according to the amount of spark advance it wants to add to the base timing, and sends the modified timing signal back to the ESC module over the white timing output wire (on the 4 contact connector). The ESC module uses this signal to switch the white coil output wire (on the two contact connector) either open, or to ground. The pink wire on the two prong connector supplies +12 volt ign power to the ESC module. The tan / black wire on the 4 prong connector allows the ECM to switch timing control over from the ESC to the ECM, after the engine RPM is above a few hundred RPM. Disconnecting the tan / blk wire makes the ESC module control the timing exclusively. This is done to set the base timing on the engine.

You would have to consult MSD on whether the MSD pickup coil would work in place of the GM pickup coil - the MSD coil impedance and output level would have to be compatible with the GM ESC module. You could use the entire GM distributor & drive your MSD-6AL with the white (two contact connector) coil output wire from the ESC module.

Tim

 

Thanks Tim,

That is EXACTLY what I needed to know!