Totally weird fuel pump issue
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Senior User
Joined: Apr 2005
Posts: 453
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From: medford oregon
Totally weird fuel pump issue
I just replaced the front tank and fuel pump a month ago. The tank was nasty and the pump float was rotted as well as the pump not running. The whole unit worked great for the last month until a couple days ago I started down the road and the truck started stumbling and died. I pulled over and noticed the fuel was low in the filter so I switched it to the rear tank which still works.
I jumped the relay and the rear pump runs but when I switch it to the front pump theres no action from the front pump. Heres the weird thing, with the relay jumped and the rear tank selector and ignition on the rear runs but when I switch to the front with the relay jumped it wont run until the ignition switch is off. Then it runs but no fuel comes out like its running backwards or something. Theres obviously power getting to the pump with the ignition off and the relay jumped.
This is a brand new Carter pump and a new fuel tank so Im kinda stumped. Any ideas out there?
I jumped the relay and the rear pump runs but when I switch it to the front pump theres no action from the front pump. Heres the weird thing, with the relay jumped and the rear tank selector and ignition on the rear runs but when I switch to the front with the relay jumped it wont run until the ignition switch is off. Then it runs but no fuel comes out like its running backwards or something. Theres obviously power getting to the pump with the ignition off and the relay jumped.
This is a brand new Carter pump and a new fuel tank so Im kinda stumped. Any ideas out there?
New User
Joined: Jun 2013
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Did you replace the fuel tank switch/ valve? I had a diesel (1984) and it would do nothing but suck air from the return line(bad selector valve). I just hard lined to one tank and it ran great till I got another valve.
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Senior User
Joined: Apr 2005
Posts: 453
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From: medford oregon
I didnt replace the switch valve because it seemed to work fine. You can hear the switch actuate when the selector switch is flipped. I dont think the switch keeps the power from the front pump but I may be wrong. The problem is the pump is not running when selected to the front and does on the rear. The sending unit on the front pump is working fine though.
New User
Joined: Jun 2013
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The problem I had was a lot of air in the lines. I would switch back and forth from front to rear and suck air. It left me on the side of the road many times. The switch rotted inside and would draw from the return and supply. Causing air. But in your case I would jump each pump to see if they are working then back track from there. If you only have one pump and it shuts off from tank to tank its a switch or tank valve problem I would guess.
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Senior User
Joined: Apr 2005
Posts: 453
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From: medford oregon
Im getting about 10.30 volts to the fuel pump and Im not sure what that means. Im still not sure which wires on the pump go to the pump its self and which are for the sending unit. Ill have to check it again in the morning.
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Old School Hot Rodder
Joined: Feb 2006
Posts: 6,472
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From: Exmore, VA
Voodoolord, Do a search on here, there have been several postings of the 1985 460 fuel pump wiring. I have the 1986 on my website, but it is different from 85, yours has two relays, 86 only uses one.
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pedant
Joined: Jan 2008
Posts: 23,576
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From: EXTREME southwest CT
I believe the SPDT *selector relay* default position is 'rear'
If you are powering the front pump directly it is just deadheading into the tank switching module.
Subford has the color coded wiring diagrams for the '85 setup.
If you are powering the front pump directly it is just deadheading into the tank switching module.
Subford has the color coded wiring diagrams for the '85 setup.
FTE Legend
Joined: Sep 2003
Posts: 53,994
Likes: 2,399
From: NY and VA
As mentioned go through the trouble-shooting steps. On the plug-in to pump/sending unit there a 2 grounds. 1 for pump,1 for sending unit. I went through 4 NAPA/Carter rear tank pumps. One didn't last 5 miles. Put in an Airtex working fine after a year.
Old School Hot Rodder
Joined: Feb 2006
Posts: 6,472
Likes: 11
From: Exmore, VA
One more issue I ran into on all of the aftermarket senders, the sender ground is a dummy. The Ford units had brass washers on the sender ground pin, the aftermarket ones have all four pins insulated.
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