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276 Views 8 Replies 5 Participants Last post by  vegas_ss
I have a 95 Caprice in my 66 Land Cruiser…. Going down the road yesterday and it was “stuttering” like it was running out of fuel…. Got to work and after work I went out and fired it up, was idling good and then it died. Went to start it back up and noticed that the fuel pump wasn’t running (inline after market). Towed home today, did a series of tests. Fuel rail is full and a jumper from battery to pump keeps pump running. Power lead from ECM turns pump on for a few seconds and turns off. Engine sputters like it wants to fire, but will not…. Any ideas or things to check? I think my ECM went out.
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The ECM won't power the fuel pump directly - there is (should be...) a relay between them. Check that relay
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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.

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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.
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