Can someone tell me where the fuel pump impact cutoff switch is located on a 86 ford 150 4x4. I looked in the passenger floor board but did not see one. The previous owners of the truck i got have the high pressure fuel pump wired to the red wire on the relay. This wire gets hot when the key is turned on but there is no power going to the in tank fuel pump. I know the pump is good as it will run if I send power to it from a wire at the relay. Are these pumps designed to run all the whole time the key is on or should they be shutting on & off?
Are these pumps designed to run all the whole time the key is on or should they be shutting on & off?
When the key is first turned, the relay turns the pump on for a few seconds to prime the system. If the engine starts, the computer verfies the engine is running by looking at the signals from the distributor module. If the engine is running, the computer keeps the relay pulled in, and the pump runs all the time.
This brings up a good point. It's not good for the pump to run very low fuel levels in the gas tank. The gas in the tank helps cool the pump.
The pump does not build up a lot of pressure and dead head. There is a regulator on the fuel rail that goes to the injectors. It has a return to the tank fuel line it controls. It keeps the pressure at around 40 lbs. If the pressure tries to get above 40, it directs some of the fuel back to the tank through the return line.
I believe on the 86 models the inertia switch is on the heater duct on the right side of center. That's where my 86's switch is. Do you only have the one tank or two? Unfortunately, my EVTM is loaned to a friend who just bought an 86 truck and is trying to sort out some electrical gremlins of his own.
I found the switch today and it is working properly. Has continuity when closed and none when opened. I still cannot get my fuel pump to run without straight wiring it.
There are 4 wires going to my relay:
Pin #1 Tan/grn wire---Get power from Pin #2 when key is on.
Pin #2 Red Wire---Hot when key is ON
Pin #3 Brown wire-- NEVER gets power through the relay, But pump will run if I send power to it from the yellow wire or Pin #2 red wire with key on.
Pin#4 Yellow wire -----Hot All the time even with key OFF
I was having a problem with my original relay that when I hooked up power to the battery the pump would run. I changed relays and now the pump will not run. I went back to the parts store tonight and swapped relays to one that has 5 pins , but basically the same wiring diagram on top & it still will not work. Pin #3 & #4 should connect when the switch closes, but the switch is not making. What closes the switch? I tried to show the diagram that is on the relay below. What else can I do? Any Ideas?
3 ------/ -------4
s On the relay this is represented as a curly cue line between 1 & 2
Thanks for the tips...I have narrowed it down to the wire going from the relay to the computer under the dash is not geting a ground. I traced the wire from the fuel pump all the way to the computer and it ohms out good. I can connect the wire to ground and the pump goes on and off with the key. Would it be a problem leaving the wire grounded. The control power goes on and off with the key. Thanks for any advice.
The ECM is supposed to ground the relay for a few seconds on power up, then ground it during cranking and with the engine running. It gets its engine running signal from the distributor. If you leave it grounded, it will work, but you loose the fuel shut-off if the engine stalls. One of the issues I have run into on these is the ECM ground, it is near the battery on 86 trucks, a bad or missing conection will drive you bats. Once my EVTM manual returns, I will scan the appropriate pages and post them on my website for all to see.
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