ECM?

The ECM won't power the fuel pump directly - there is (should be...) a relay between them. Check that relay

Ok….. how do I check the relay

If the engine is getting fuel, it should start…. I by passed that system, engine will not fire

To add….. the power lead from the computer ran the fuel pump constantly, up until yesterday

Assuming you have a relay - The ECU will send power to the coil of a relay - this is a low power/current circuit, maybe 0.01 amps, small wires, etc.
The relay should make an audible "click" when it has power on one side of the coil and ground on the other.
If it doesn't click, you need to determine if it doesn't have power, ground or if the coil on the relay is bad.

What system did you bypass?

If the pump is running, have you checked fuel pressure at the engine?

If you were really pulling the FP 10+amps through the computer, then you probably fried the computer.

-Brian

On a stock LT1, the oil pressure switch takes over after starting. It's wired in parallel with the relay. I can pull the FP relay on my Caprice after starting and it will keep running. Unsure if your swap was done this way. But it's the way it's supposed to be. I never did verify if the computer really keeps the FP relay energized the whole time or just at start, I'd have to consult the FSM on that one. But I always assumed the relay dropped out as a safety feature. Engine stalls (ie: accident) or low oil pressure, then no fuel until you recycle the key.

Also unsure how you got a constant voltage in your experience other than you were just reading a backflush signal from the relay.

Edit: FSM states they are wired in parallel as a "backup" in case of relay failure. No indication that this is a safety feature or not.

Really need a fuel pressure gauge to troubleshoot properly. The presence of fuel in the fuel rail doesn't mean much and your symptoms are that of a bad fuel pump/insufficient fuel pressure.