How does electronic timing advance work on a TBI distributor?

[MANIAC]

Okay so after a trip to pick n pull and pulling proms I found that while they didn't have any that would work with mine none of them looked like min so after looking at it like a fool for like 20 minutes I pulled my ECM prom from a chip that was put on it that got burnt up in place of the prom so after installing it without that chip now my obd1 port works and I gotta change my ICM again because it burnt out yesterday but after I change that out and check if the timing issue is fixed I will let you guys know what I find out but that's the update so far and the only code it's throwing is knock sensor but it's the 96-99 knock sensor which I don't think is the same as the 88-95 ones but who knows. Either way I'll keep you guys posted on the progress

 

[Schurkey]

I pulled my ECM prom from a chip that was put on it that got burnt up in place of the prom so after installing it without that chip now my obd1 port works

I'd like to see photos of this mysterious "extra chip".

and I gotta change my ICM again because it burnt out yesterday

Repeat failures of ignition modules is almost always due to a failed ignition coil.

Test your coil with an ohmmeter to start with. You need to measure primary resistance, (typically about 0.5 ohms) secondary resistance (check the service manual for spec) and then primary and secondary to ground (no continuity allowed--must be infinite resistance/open circuit.)

THEN, if your coil passes all those tests, use a spark tester calibrated for HEI to verify voltage output. Ideally, you'd drive around for half-an-hour to get the coil fully hot, then connect the spark tester and have someone crank the engine while you mist the top of the coil with water from a squirt-bottle and look/listen for regular (not erratic) sparking across the spark-tester's gap.

I will let you guys know what I find out

Yes, please.

the only code it's throwing is knock sensor but it's the 96-99 knock sensor which I don't think is the same as the 88-95 ones but who knows. Either way I'll keep you guys posted on the progress

Sounds good. You absolutely need the correct knock sensor.

 

[AuroraGirl]

I'd like to see photos of this mysterious "extra chip".


Repeat failures of ignition modules is almost always due to a failed ignition coil.

Test your coil with an ohmmeter to start with. You need to measure primary resistance, (typically about 0.5 ohms) secondary resistance (check the service manual for spec) and then primary and secondary to ground (no continuity allowed--must be infinite resistance/open circuit.)

THEN, if your coil passes all those tests, use a spark tester calibrated for HEI to verify voltage output. Ideally, you'd drive around for half-an-hour to get the coil fully hot, then connect the spark tester and have someone crank the engine while you mist the top of the coil with water from a squirt-bottle and look/listen for regular (not erratic) sparking across the spark-tester's gap.

Yes, please.


Sounds good. You absolutely need the correct knock sensor.

1997 PCMs have an additional kncok component on the case
But they did away with that after a year, and then were gone of the chips entirely because 1996 obviously uses no PROM for the main thing

but there could be auxillary knock related memcals in the older ECMs too, because thats just how it worked.

 

[AuroraGirl]

www.repairpal.com/gm-obd-I-code-chart

GM OBD I Trouble Code Chart

Code Description Code 12 No distributor reference pulse (diagnostic test active) Code 13 Oxygen sensor circuit open or no

repairpal.com

@MANIAC What is your trucks VIN number, i can tell you a list of PCMs and the PROMs which will work, and how to know which is neeeded. also need to know if federal, california, or export emissions.

 

[MANIAC]

@MANIAC What is your trucks VIN number, i can tell you a list of PCMs and the PROMs which will work, and how to know which is neeeded. also need to know if federal, california, or export emissions.

I will send the vin in the morning when I got some daylight but on another note truck is finally fixed turned out it was chipped being that it was an ex fire chiefs vehicle I shouldn't have been surprised but in either case the chip had burnt out which was why I couldn't get any codes and the ECM would not advance the timing it's all good now that I've removed the chip and just plugged in the prom but I wanted to let you guys know

 

[AuroraGirl]

I will send the vin in the morning when I got some daylight but on another note truck is finally fixed turned out it was chipped being that it was an ex fire chiefs vehicle I shouldn't have been surprised but in either case the chip had burnt out which was why I couldn't get any codes and the ECM would not advance the timing it's all good now that I've removed the chip and just plugged in the prom but I wanted to let you guys know

HI