What inputs cause the ECU to make the switch to send ground to the injectors making them fire?

I am troubleshooting a no start issue documented here:

https://www.yotatech.com/forums/f116...-start-251387/

Also is there anyway to verify the output of the ground signal from the ECU to the injector? I have unwrapped the harness and verified the wiring between the injectors and the ECU and reran the grounds for the ECU direct to the battery.

Swapping in a new ECU didn't help so trying to figure out what's keeping the injectors from firing, including the cold start injector.

Matt

 

I am chasing same problem, have good spark and runs on eather, fuel pressure to rail but no gas to cylinder. New engine, wondering if I missed a connection somewhere

 

Not really sure what you are trying to say here. If you measure with a voltmeter from #10 to ground and #20 to ground at the ECU with the Key on, you will measure probably a bit less than battery voltage. The ECU fires the injectors by completing the circuit to ground internally. If you have a pre mid 88 system that voltage value will be lower due to the impedence of the injector and the resistance of the solenoid resistor that is in the circuit. After mid 88 there is no solenoid resistor and the only voltage drop will be due to the impedence of the injector.

If nothing is firing, I would start my continuity checks at the EFI fuse, EFI main relay, solenoid resistor if your truck has one, and the Wiring to the ECU.

Jagman60, you say you are getting fuel pressure to the rail, but is it enough fuel pressure for the engine to start? I'd install a temporary fuel pressure gauge to see if it is within spec.