Question : 3400 just quits - need help with diagnosing

[GaryW]

Running a 3400 (LA1) with DIS / 7730 ECM. Last couple weeks while driving, engine just suddenly quits. Starts up, goes for a bit, then quits. Same behavior parked in the garage. Swapped in a new ICM, as same problem a year ago when alternator went and took out ICM with it. New in the last year: all 3 coils and ignition wires, ICM (this week), CPS. Fuel pressure reads 50psi on the rail even when it quits.

Tuner Pro tracings attached. 1st and 3rd run show the intermittent quitting. 2nd run ran for several minutes without a problem.

Would appreciate thoughts on how to chase down the problem!

[autosmith]

1227730's were notorious for cold solder board cracks (although I'm sure by now you have this sorted already).
Best way to test is to drop the ECM and let hang down. Run car setting heater to high on floor vents, after several minutes lightly tap the ECM near the PROM access door, if she stumbles/dies you found it.
When you get another ECM be sure to very gently install the PROM removed from your original ECM: insert into socket lightly and fasten the side retainers into place allowing them to pull the PROM into seated position. Be sure to remove any cork or foam gasket on the PROM door that will contact the PROM as this pressure is enough to create an issue later.