Question about 1988 Ford F 150

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No power to fuel pump

Replaced fuel pump, relay switch, and checked kill switch, no power to pump when i turn the key over what could be the problem?

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  • rerun2marie Mar 03, 2009

    new fuelpump, does work when tested to battery , not when installed

  • rerun2marie Mar 03, 2009

    new fuel pump test to battery works fine

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I had the same problem, for the longest time I couldn't figure out why the pump wouldn't work....I don't know if your solution is the same as mine was but look to see if you are missing the connection wire that goes from the negative connection at the battery (should be a wire that sticks right out of the actual connector on battery) to the wires that run alongside the front rail and radiator. This goes right to the PCM and was my problem. Let me know ;)

Posted on May 05, 2009

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Replace the fuel pump.

Posted on Mar 03, 2009

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1 Answer

I replaced the turn signal switch and now it wont start. i can hear the fuel pump kick on. makes no sense


You said you hear the pump come on, then said fuel pump not running ???
Check the fuse for the pump, preferably with a test light to verify power is there. Key must be in on position. If the fuse is powered, feel for the fuel pump relay to click when you turn key to on. Put your finger on it while someone turns key to on. If it clicks, check for power at the tank connector on the pump wire, while the engine is cranked. If power there when cranking, the pump must have failed and needs replacing. If the relay clicked with key on, and no power at the pump wire at tank while cranking, then check wiring from relay to pump connector-the fuel wire may have broken.
If the relay doesn't click when key turned on, check for the power feed for the pump at the relay terminal. If the relay has power available to be transmitted to pump, then the relay's signal from the computer or the ground side of the relay's coil signal (from the computer) may need checked.
If the pump is working, and you have good pressure in the lines, check the injector circuit. Also a fused circuit, so check the fuse first. The injector should have a steady voltage signal to it with key on. The injector only has two wires, the power wire and the ground wire which goes to the computer. When the computer momentarily grounds the injector circuit, the injector "pulses", causing fuel to spray out the bottom.

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What shuts off power to fuel pump when key is turned off on a 94 GMCwith 350 engine


Power is fed to the pump by a fuel pump relay. The relay is powered by a fuse but is triggered by the computer. So when you turn the key on, the computer triggers the relay, the relay closes and turns on the fuel pump. Power is cut off only when the key is shut off and the computer kills the trigger signal to the relay

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1 Answer

Car will turn over but won't start. Through the


No noise from fuel pump when you turn over the car .First thing get voltage at fuel pump relay checked, is there 12 volt to the relay.If no, then problem is again the relay.--------- To reconfirm the problem, try other test, that is remove the relay and by pass the relay terminals with a jumper wire .Then with 12 volt external battery give power to fuel pump connector and see, if the fuel pump starts, then its clear that fuel pump relay is faulty.----------- Also other problem can be fuel pump inertia switch.If the inertia switch is faulty then also fuel pump will not start.-------- The fuel pump relay on a 1995 Ford Explorer is in the power distribution
box, in the engine compartment, driver's side near the firewall.----------
The fuel pump inertia switch is in the right front passenger area
it is below the dash but above the carpet in the right hand corner.--------
Its a push button type inertia switch.
--------
Fuel Pump Activation
When ignition switch is turned to START position, PCM operates fuel pump relay to provide fuel for starting engine. PCM senses engine speed and shuts off fuel pump by opening ground circuit to fuel pump relay when engine stops or engine speed drops to less than 120 RPM. When ignition switch is in ON position, EEC power relay is energized (contacts closed). Power is provided to fuel pump relay and timer in PCM. Fuel pump receives power through fuel pump relay contacts.
Inertia Fuel Shutoff (IFS) Switch
All models use an electrical interrupt switch in fuel system. During a collision or vehicle rollover, electrical contacts within inertia switch open, shutting off fuel supply to electric fuel pump. Fuel supply is interrupted even when engine is running.
A reset button is located on switch assembly. If electrical circuit trips, vehicle will not restart until switch is reset. Fuel system should be inspected before resetting switch.
IFS switch is located under instrument panel, near right side of transmission hump.
----------- If the fuel pump relay, the inertia switch and fuel pump all checked ok, and fuel pump is working with direct 12 volt source to fuel pump.Then problem relates to computer.The computer (power control module, PCM) is faulty and has to be replaced.--------- This will help.Thanks.Helpmech.

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1 Answer

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Model? Year?

Check per owner manual to be sure inertia switch is not tripped. Remember, fuel pump only runs for 5 seconds when key is turned ON, then it shuts off if engine is not running. Pump always runs when key is in START position.
Listen for pump to run inside fuel tank for 5 seconds after key is ON.

The PCM power relay turns on the PCM and the PCM turns on the fuel pump relay, which turns on the fuel pump.

See owner manual forfuse & relay charts.

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When you turn on the key to Run, do you hear anything? There is an Inertia cutoff switch which kills the power to the fuel pump. This switch is usually behind the front kick panels and has a reset button that you push. It is a safety switch and can sometimes trip if a doorslam or impact is felt by the sensor.

There can be a Fuel pump relay in the black powerboxes, but there is no Code, so it should be okay. If you have a gauge to measure fuel pump pressure, check to see if the fuel pump is working by measuring pressure at the fuel rail.

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3 Answers

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1 Answer

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