Checking the ECU, AFAIK is by process of elimination, as in my earlier post; it(the case) must be grounded back to the battery; through the sheetmetal is fine. Usually; passenger-side apron to core-support to jumper to battery negative. There should also be a redundant ground strap from the rear of the passenger-side head to the firewall, but this has nothing to do with your problem....... unless both grounds are faulty!
You could build a tester; all you need is a spare Distributor, a coil,a ballast. and a battery .......... which are already under the hood. You just need to verify that they are all in good working order.Once you have done the diagnostic a time or two and have built the jumper wires, it only takes a few minutes to run thru the tests. I have done them on the side of the hiway several times. It was never the ECU, and since I installed the big yellow SuperCoil, it has never been the coil. For me, if it quits while driving, it's either the ECU ground return path, or the pick-up. If it won't start it has always been the ballast resistor.
That Ballast is always cooking itself, that is how it works. Eventually it just cooks itself to death, or the connections to it go bad. If you own a car with this system on it you will always carry a spare.
