Fuel Pump Relay?
Lead Driver
Joined: May 2004
Posts: 6,461
Likes: 6
From: Abilene Kansas
the relay gets power from the switch. it takes this power and turns on a circuit to power the fuel pump. its basically a powered switch (like a light switch) only electricity switches it on and off. if it is failed the fuel pump will not run.
Matt
Matt
Elder User
Joined: Mar 2005
Posts: 524
Likes: 0
From: Liberty, MO
Something that'll indicate a non functional fuel relay is if out of nowhere it takes a seemingly long time to start. IF it starts at all. Try switching your fuel pump relay with the replay for the computer, that'll tell you right away!
Posting Guru
Joined: Feb 2006
Posts: 1,448
Likes: 1
The function of the relay is to control the fuel pump under various conditions. This relay has two parts. One part is the relay coil, and the other part is the electrical contacts that open and close. The actual switch in the relay.
Current flowing thru the coil will cause the contacts to close completing an electrical circuit to supply power to the fuel pump via the inertia switch.
The electrical supply to the contact side of the relay is there all the time coming from a fuse in the fuse box.
The electrical supply to the coil side of the relay comes from the EEC relay. For current to flow thru the coil, it must have a ground. Grounding for the fp relay is controlled by the computer depending on the action called for.
At ignition switch turn on, EEC relay closes supplying power to the fp relay, and the computer is supplying ground for approx 2 seconds, then releases the ground. This primes the fuel lines with fuel.
The ignition switch is then turned to the start position, the engine begins turning over. The computer detects electrical pulses from the ignition spark circuit, and re-grounds the fp relay coil starting the pump to supply fuel for engine start/run.
The relay contacts can stick, pump will run all the time. The coil can become weak (shorting or high resistance) and cause slow/no pump start. Coil contacats can become contaminated causing no/intermittent start. jd
Current flowing thru the coil will cause the contacts to close completing an electrical circuit to supply power to the fuel pump via the inertia switch.
The electrical supply to the contact side of the relay is there all the time coming from a fuse in the fuse box.
The electrical supply to the coil side of the relay comes from the EEC relay. For current to flow thru the coil, it must have a ground. Grounding for the fp relay is controlled by the computer depending on the action called for.
At ignition switch turn on, EEC relay closes supplying power to the fp relay, and the computer is supplying ground for approx 2 seconds, then releases the ground. This primes the fuel lines with fuel.
The ignition switch is then turned to the start position, the engine begins turning over. The computer detects electrical pulses from the ignition spark circuit, and re-grounds the fp relay coil starting the pump to supply fuel for engine start/run.
The relay contacts can stick, pump will run all the time. The coil can become weak (shorting or high resistance) and cause slow/no pump start. Coil contacats can become contaminated causing no/intermittent start. jd
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rulam
1987 - 1996 F150 & Larger F-Series Trucks
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Mar 20, 2006 08:11 AM
