Fuel pump issue (maybe)
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Tuned
Joined: Jul 2011
Posts: 350
Likes: 3
From: Sacramento, CA
Fuel pump issue (maybe)
My 1998 F150 4.6l will run well in the morning and the evening. If I run it during the heat of the day, it acts like it's running out of fuel and then die. And then won't turn back on until the evening. I was hunting for vacuum leaks and anything I could think of but nothing made it better. Then I noticed when I tried to turn it on, after having sat for awhile, I wouldn't hear the fuel pump prime. So i listened a few times. Every time it wouldn't start, i wouldn't hear the pump prime and every time it would start, i could hear the pump prime. I replaced the fuel pump relay but that didn't help.
So a couple questions. Before i replace the pump I want to make sure power is getting to it. I pulled the bed and there are four wires going into the pump. Looks like a pink/yellow, pink/black, dark blue, and a yellow. Which one of these wires will be live when I put the ignition switch into the on position? And will the wire stay live in the on position or will it only be powered long enough to prime the fuel system?
thanks
So a couple questions. Before i replace the pump I want to make sure power is getting to it. I pulled the bed and there are four wires going into the pump. Looks like a pink/yellow, pink/black, dark blue, and a yellow. Which one of these wires will be live when I put the ignition switch into the on position? And will the wire stay live in the on position or will it only be powered long enough to prime the fuel system?
thanks
Hotshot
Joined: Jan 2004
Posts: 19,760
Likes: 1,079
From: St Louis
Pink/black is pump power, black is ground. The other two wires are for the fuel level sender circuit.
You should have battery voltage for only about 2 seconds when you first turn the ignition switch from OFF to RUN, then it will drop to some random voltage from 3-8 volts.
You should have battery voltage for only about 2 seconds when you first turn the ignition switch from OFF to RUN, then it will drop to some random voltage from 3-8 volts.
Senior User
Joined: Jul 2017
Posts: 278
Likes: 1
From: Penticton, BC, Canada
Sounds like the exact same thing that happened when my fuel pump bit the dust. Replace the fuel filter at the same time, because it will be filled with pump schrapnel from the failure.
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Tuned
Joined: Jul 2011
Posts: 350
Likes: 3
From: Sacramento, CA
I tried to test the power going into the pump yesterday but it was oddly cool out. It has been 102 to 109 everyday for the last few weeks but yesterday was in the 80's so the truck (for the first time in a few weeks) did not stall. I already had the bed off so I went ahead and changed the pump and filter. I did notice that the fuel coming out of the fillet was black as oil. Anyway, i'll get to 100 today so I shouldl know for sure today.
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