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Discussion Starter · #1 ·
Start problem. I have read so many things about htis problem and still havnt fig it out . Here it is . I have a 91 mustang gt 5.0 all stock aod. When turning on ignition fuel pump runs continuesly and doesnt run its intial 5 to 20 second and cut off . The car has fire and fuel pressure injectors have 12 volts . I replaced the prssure reg and tried the relay but mine is 4 prong and the auto parts sells 5 prong . When i use the 5 prong the pump doesnt come one at all . I jump the wires where the fuel pump relay plugs in and the pump runs and the car startes but pump runs cont again . Only dif is the car starts . Please help.
 

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Sounds like the ECM is not switching the ground off. Or someone has wired it to run constantly.

Did this just start all of a sudden, or has it always been like this?
 

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Discussion Starter · #3 ·
It just started all the sudden . Every now and then i can get it to work correctly and it starts but once i shut it off ot wont restart and pump still runs in on pos but no start, weierd .
 

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Turn the car on, not running, and try tapping on the relay and see if it switches off.
 

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seems like a relay issue, because you havent tried a new relay and if you jump it, its working fine, so the contacts in the relay are engageing and then not disengaging, so its either the relay or someone messed with the wiring check the wiring before getting a new relay its only a short run to trace
 

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I just posted this same message to another thread. On my '91 when the fuel pump wouldn't come on it wasn't the relay, but the plug that the relay connects to. One wire had corroded. I got it at Napa for $16, and had to splice the 4 wires and then vroom vroom. Best of luck. Napa's part # on the sheet is "1991 Ford Mustant 5.0L 302 CID EC199". I assume that the "EC199" is all you'll need.
 

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If the relay is good, and its connector, Then the ECM is not switching the ground like it should. My Coupe has the pump wire to run all the time, was like this when I got it, I just don't feel like taking the interior back apart ti mess with it. No problems here. But the ECM is what controls the relay, It switches the ground on and of depending on if the car is running or not. I wouldn worry about it IMHO. As long as the pump is running your fine.
 
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