88 GXL No Injector Pulse or Spark
 

I have a 5spd 88 GXL that was running great and has for years. Never had any issues with the car. Parked it one evening last week and I went out to start it the next day and it will not start. I confirmed that I am getting no spark and no injector pulse on the primary injectors. Main relay appears to be fine. Everything powers up and works fine. All fuses checked and rechecked. A spare CAS was plugged in and spun with a spark plug attached to a plug wire and I get one spark when I spin the CAS gear and nothing else after that initial spark. The key must be turned off and then back on to get the one spark. Tonight I cleaned the injector grounds on the top of the engine and checked for any breaks or rodent damage to the wiring. I found none. My next step is the ecu. Such a strange thing to have happen randomly overnight. Any insight would be appreciated. Double checking here to make sure I'm not missing anything. I trust the judgement of the forum.

Attachment 746962

Any other thoughts or suggestions?

This is indeed very weird. The stock ECU just isn't smart enough to deactivate certain features. Do you still have 12v on one of the injector wires before and after it sparks/quits?
The CAS connector tends to get finnicky as it ages, but the consistent failure mode doesn't line up with that.
I'd hit all the grounds and then turn to the ecu.

I did overlook the rest of the grounds as a possible suspect. Even if they aren't what's causing the issue, it wouldnt be a bad idea to get them all cleaned up and then inspect the ecu and the wiring near the ecu for possible rodent damage.

I did not check for any voltage at the injectors with a multimeter. I simply used my noid light on it while my son cranked the engine over and we got no injector pulse. I can always take a video of the issue and see if I can post a link to it if anyone would like.

Also, check the EGI Comp fuse closely and verify you have 12v coming out of the main relay

Have you checked the EGI INJ fuse? The EGI INJ fuse feeds only the injectors and coils.

I will verify that I have 12V coming out of the main relay. I did verify that the main relay was full operational last night and I cleaned all of the grounds, tapped the welded nuts, and replaced the bolts with new bolts that secure the grounds.

I did visually inspect the EGI INJ fuse but I did not run a continuity test on it or swap with a known good one from my 10AE. I can do this tonight after work and report back! Thank you both for the suggestions!