My 1988 IROC shows error code 12 when I use the safety pin trick. It is "No reference pulses to the ECM! Is this a fault in the ECM or one or more sensors??? HELP!

 

This is correct, just telling you that the engine isn't running. The missing reference pulses would be from the distributor if running.

RBob.

 

My mechanic came over and used his computer to check the code to be sure, and it was only showing code 12 when it was not running, and code 42 when it was running. I think its the EST but the 42 codes are: Fault at electronic spark timing circuit OR Fault at direct ignition system OR Fault at fuel cutoff relay circuit.
Any advice?

 

Code 42 will also be set when the EST bypass connector is opened to set the timing. So if the timing has recently been set. . .

Reset the ECM (battery dance) and see if 42 comes back. If so, then I'd check the connectors at the distributor and then possibly swap the ignition module (in the distributor). Can also be the pickup coil or the ignition coil.

RBob.

 

Thanks RBob! I will check those things. Also, I wanted to see if the computer itself was fried, so I used an old 305 ADS Super Chip that I had and installed it in my 350 and it still shows the same symptoms. Does this mean that the computer is fine, and it is for sure something else? Also, I just did the Throttle Body coolant bypass, i dont see why that would have anything to do with it, but is it possible? Thanks again!

 

A different chip won't define whether the ECM is good or bad. The TB bypass won't have any effect on the 12/42 error.

Do the battery dance first (disconnect negative lead for 5 minutes and reconnect) before doing anything else. If any codes come back then the tap test is next.

Your '88 uses a '165 ECM that is prone to intermittent problems. While the engine is idling tap on the ECM. If the engine stumbles, misses or otherwise misbehaves, there is a good possibility that the ECM is bad.

RBob.