Hello,
Probably my car is kinda too old to this forum, but you guys seems to know a lot about DFI system.
My car is Cadillac Seville from 1980, engine is 368 without 8-6-4.
So, I bought this car two weeks ago. It cranked, but won't start. After some adventures with dirty intake manifold i tried to start this car.
Thing is, that I can't manage why injectors aren't working. Spark is good, short grounded injector connector show power on bulb. When just putting some petrol to throttle manually, it starts for a seconds.
Today I was working on it all day and figured that signal from HEI module to ECM is okay, power to ECM is okay, ground to ECM too.
Fuel pump is working for 1 second after ignition ON, and according to service manual it's correct. And then working also when engine rpm is higher than 200.
I checked power to injectors, voltage measured in connector is 12v for one second after turning on ignition (same with fuel pump), when cranking it's about 8v, can't figure out why, it can be because of pulsing of ecm ground? But if so, why testing the same connector with bulb, it doesn't show any light?
Also when measuring injectors voltage it's okay until I connect bulb too. After that, voltage is 0. What does it mean?
Testing with bulb and outside ground source light up bulb, so there's power for injectors for sure. But it seems to be missing ground.
Also checked injectors resistance. All good.
I tried to check if injectors are okay and grounded connector. Injectors are now constant open.
ECM seems to be 1224539
New HEI module.

 

sounds like your ecm is switching ground to the injector to turn it on and off. this is the most common way of doing it even today. so basically your ecm is not firing the injectors. either because of something else not telling it to, or bad mosfit in the ecm itself.

you're going to need to find some kind of scanner to read live data from the obd1 port. once you find that look for rpm while cranking first.