Chevrolet Repair: check engine light strobes, gm training center, timing light

Question
Truck is a 92 chevy K-1500 5.7 engine. local shop replaced ECM and dist, and dist cap. now as soon as you turn the key on service engine strobes like a timing light. When the modus tester is pluged in the light stops but says no communication. Any suggestions besides towing it to a dealer. Any help would be appreciated. This truck was towed to shop for a dying upon starting. It would run approx 15 sec and die. Now it starts but as I said the engine light strobes like a timing light.

Answer
Hi Mike,
Years ago when I was in a GM Training center class, something like that was mentioned.
Seems he said if connecting the scan tool made it run better, that it was probably a bad ground to the ECM, and the scan tool was supplying a good ground.

I never ran across it, but sure rings a bell.

Van