Anyone ever see a TPI setup that won't go into bypass mode? My buddy picked up this '86 bird dirt cheap cuz it wouldn't run worth a turd. That ended up being it had too big of injectors installed and a ruptured fpr. I wanted to check the timing, so I found the est bypass connector and opened it, but the check engine light didn't come on and the timing mark didn't move. I checked the wire from pin B at the distributor to the bypass connector and on to the ecm at pin C7 and all is good. I'm thinking it has something to do with the ecm and/or memcal because it's an aftermarket reman ecm, 730 ecm btw, and it has a JET memcal in it. BTW, this car was supposed to have a 2.8 in it according to the vin but has a 90-92 speed density 305. Runs pretty good but I still want to check the timing cuz it has bad spark knock on hard accel.
Plus the yahoo's that had this thing before had nitrous on it who knows what they've hacked into. So, no EST bypass mode. Bad ECM? MEMCAL? Ignition module? Wiring issue? I did find a wire spliced into C8 Spark timing output, at the ecm but don't know where the other end goes to so I just unspliced it. Can't check it yet, engine is out for other reasons and I wanted to address this issue before getting it back in and trying to set the timing again. Watchya think?

 

I'd say that the ignition control module (ICM) is bad. When the EST/BYPASS is opened the ICM sees this and pulls the EST line low along with running at base timing. The EST/BYPASS is a signal from the ECM to the ICM.

The EST line being pulled low is what the ECM sees and then sets the SES light and code 42. The EST is a signal between the ECM and the ICM. The ECM pulses it for coil dwell and spark timing.

The ICM holds it low as long as the EST/BYPASS is active (open). Which the ECM does during cranking, then once running the ECM closes the EST/BYPASS signal to take over timing.

So, with the EST/BYPASS open, no base timing and no SES, ICM is the guilty party.

RBob.