A few days ago, I was almost home and the engine quit. No unusual noise, no faltering, just off.
The fuel pump sounds like it's working normally, the injector appears to be delivering fuel normally, and the rockers are still rocking. Suspecting the coil, I swapped in another used but known good coil. The engine started up instantly then died within a second.
Both coils test ok with the 3 step factory service manual resistance checks.
Is your car a standard or automatic? This is a long shot but try this: If your car is a standard transmission unplug the connector to the clutch safety switch and jump the plug with a wire or a large paperclip then try to start the car. Its possible that the contacts inside the switch are corroded and when a large shot of current hits them they only work for a couple of seconds and after that its an open circuit. If its not that it could be in the ignition switch.
If you have access to another ECU, it might be worth swapping that out as well to see if there is any change at all.
The ECU on my 84 failed, causing in the engine to simply shut off when other wise running perfectly without warning and without any check engine codes.
Ding, ding, ding! We have a winner! edfiero had the correct answer! Woohoo!
A couple of years ago, I replaced the rattling 2.5L in my '86 with a 2.5L from an '87. Today, I replaced the 31 year old 367,600 kilometer ECM in my '84 SE 4 speed with the surplus ECM from the '86. The engine started right up and seems to be running normally. As I suspected, the shift light comes on to suggest 5th gear, but since I don't have one, I tilt the wheel so I can't see the light. The light goes off over 3,000 RPM; about 100 kilometers per hour or 62 mph. I presume if I swapped the PROMs, that issue would disappear.