Fuel gage troubles
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Senior User
Joined: May 2002
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Fuel gage troubles
Bought my "new" truck, a '91 F-150 XLT, 302, "cuse me, "5.0" long wheel base 'xtended cab with dual tanks, all for $500.
Guy I bought it from disclosed all kinds of small gremlins that I can handle for the most part, but this has me boggled.
Rear Fuel pump was changed, and the gauge quit working.
Checked plugs, secure.
Pumps comes on when key turned on. {both front and rear tanks}
Checked power to plugs.
Getting 8 1/2 volts on, counting from left, spot 2, 6 1/4 volts on spot 3. Spot 1 and 4 zero volts.
This is on both front and rear plugs.
Checked selector switch, voltage the same on corresponding wires.
Switch appears to work fine.
Haven't gotten to the gauge yet, but am wondering if I am missing anything.
Any ideas??
Guy I bought it from disclosed all kinds of small gremlins that I can handle for the most part, but this has me boggled.
Rear Fuel pump was changed, and the gauge quit working.
Checked plugs, secure.
Pumps comes on when key turned on. {both front and rear tanks}
Checked power to plugs.
Getting 8 1/2 volts on, counting from left, spot 2, 6 1/4 volts on spot 3. Spot 1 and 4 zero volts.
This is on both front and rear plugs.
Checked selector switch, voltage the same on corresponding wires.
Switch appears to work fine.
Haven't gotten to the gauge yet, but am wondering if I am missing anything.
Any ideas??
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Joined: Jan 2001
Posts: 56,984
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From: Virginia
At the rear plug you should have a yellow light blue and a brown white. The yellow/light blue is the sending unit fuel level wire, and the brown/white is the pump power.
With the key in run, and the switch in the rear tank position, have someone watch the gauge while you ground out and unground the yellow/lightblue. The gauge should swing back and forth. If it does, the wiring, the switch and the gauge are ok, and there is something wrong with the sending unit.
With the key in run, and the switch in the rear tank position, have someone watch the gauge while you ground out and unground the yellow/lightblue. The gauge should swing back and forth. If it does, the wiring, the switch and the gauge are ok, and there is something wrong with the sending unit.
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Haven't been able to drop the rear tank again, but the lt blue w/yellow on the front tank, taking the plug off, the gauge goes to "max" full, grounding out the wire makes it go back to empty.
Where do i go from here?
Where do i go from here?
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Fleet Owner
Joined: Aug 2005
Posts: 23,667
Likes: 301
From: Easton,Ks
If the rear gauge quite when the fuel pump (FDM) was changed and you used the old sender I would say the sender was messed up when the FDM was changed.
If the whole unit was changed from the top plate down then I would say the unit has a bad sender and you need to put your old sender back on.
There are only two screws that hold the sender on,
Image of the unit (FDM):
http://i54.photobucket.com/albums/g9...veryModule.jpg
/
If the whole unit was changed from the top plate down then I would say the unit has a bad sender and you need to put your old sender back on.
There are only two screws that hold the sender on,
Image of the unit (FDM):
http://i54.photobucket.com/albums/g9...veryModule.jpg
/
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Thread Starter
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Senior User
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OK. All this was done before I bought the truck. Would the rear sending unit knock out the front one also? 'cause neither one works, and that's where I am trying to go. I can't see how changing the pump in the back could make the front sender unit not work unless there is an electrical problem somewhere.
Fleet Owner
Joined: Aug 2005
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From: Easton,Ks
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Moderator
Joined: Jan 2001
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From: Virginia
Do this same test with the rear tank, and if it does the same thing(the gauge moves back and forth), then the gauge, the switch and the wiring to the rear are ok, and there is something wrong with the rear sending unit.
