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post #1 of (permalink) Old 01-28-2000, 04:47 PM
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fuel pump wont shut off

I turned the key to the "on position" today to listen to the radio. (with the engine off) and I noticed the fuel pump didnt shut off. It is to my understanding that when you turn the key to the "on position", the fuel pump turns on, and shuts off after 10 seconds if you dont start the truck. Well, mine doesnt shutt off. I disconnected the battery so it wouldnt run all day. Any help? thanks!!!

Roland

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post #2 of (permalink) Old 01-28-2000, 06:26 PM
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Re: fuel pump wont shut off

I usually use the "ACC" position to just listen to the radio! :-)

Most/all the FI vehicles I have worked on (including non-Ford) pressurize up the Fuel Rail if you do a key "ON". Then, if the engine is not turning (which it shouldn't be, if ya just did key ON), the computer turns off the pump after a second or so. The pickup that the computer looks at to see whether engine is turning is Crankshaft Position Sensor, or Distrib, or some such thing that shows it's actually turning. The computer starts a timer, for how long since it turned the pump relay on, and it times out and shuts down the pump relay if no turning within that period. Turning key to "OFF" resets the routine, so turning back to "ON" triggers it again.

You lost me on one part... does your pump keep running even with key "OFF"? If so, if you locate and unplug the pump relay, and check it with a DVM (ohmeter) to find which pins on it are the Relay's coil, you could rig up a simple low-current 12 volt test light, and touch it to the socket where the relay's coil pins plug in. If it lights, then the computer is telling the relay to pull. If it doesn't light, but plugging the relay in would cause the pump to run, then it sounds like relay contacts are welded on. If so, may be able to test relay for that with ohmeter, if you can figure out the relay base. A simple test light would be a side marker or dome-light bulb (the little ones with wire folded back on the bulb base), with two wires soldered on. Solid wire, small enough to fit in the relay socket. (Using a small test light, so the computer doesn't sink more current than what the relay would normally pull).

I wouldn't just replace the computer, they rarely go bad, and that's an expensive thing to guess on. A wiring diagram and a DVM will work wonders.
Also, look around in case somebody "modified" your wiring, 'cuz they couldn't understand and fix a problem the right way, so they just wired something up (I hate finding stuff like that!).


post #3 of (permalink) Old 01-29-2000, 10:27 PM
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Re: fuel pump wont shut off

a friend of mine had that problem with his truck. it was relay switch somewhere. sorry i couldn't be more specific.


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post #4 of (permalink) Old 01-30-2000, 12:42 AM
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Re: fuel pump wont shut off

thanks guys! it turned out to be a relay for the fuel pump mounted right behind the airbox. I just replaced it and the problem was gone. Oh by the was, yes I would turn the key to the "ON" position and the fuel pump would turn on (like normal, to pressurize the system) and it wouldnt shut off, even when I removed the key. Oh well, its all good...thanks again

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