Erratic Fuel gauge
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5th Wheeling
Joined: Jun 2013
Posts: 35
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Erratic Fuel gauge
I have an 84 F150 with 2 fuel tanks. At 8mpg i really need them too 
Anyway, the fuel gauge shows when both tanks are full or when either one is full. But as I'm using up the gas, the gauge stops giving me an accurate reading. Most of the time it shows empty.
How do I fix this?
Anyway, the fuel gauge shows when both tanks are full or when either one is full. But as I'm using up the gas, the gauge stops giving me an accurate reading. Most of the time it shows empty.
How do I fix this?
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
It is probably the sending units in the tank. They are variable resistors that are changed by an arm with a float on it, which slides a contact along a resistance wire. But over the years the wire gets corroded at spots and the connection goes away at that level of fuel and the gauge goes to empty.
To test that theory you can take the wire off of the connector at the tank and put a jumper to ground. The gauge should go to FULL. Then wiggle all the wires in sight to ensure it isn't a bad connection, and have someone watch to see that the gauge doesn't move.
But, the problem is that the sending units aren't cheap. Aftermarket units like from the parts store aren't known to last very long, and ones from Ford are pricey but last better.
To test that theory you can take the wire off of the connector at the tank and put a jumper to ground. The gauge should go to FULL. Then wiggle all the wires in sight to ensure it isn't a bad connection, and have someone watch to see that the gauge doesn't move.
But, the problem is that the sending units aren't cheap. Aftermarket units like from the parts store aren't known to last very long, and ones from Ford are pricey but last better.
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
Possibly. I've seen them work better just from use - presumably the movement of the arm's contact on the wire cleans it. But I've not tried to clean one by taking it out and working on it. That's not to say I haven't taken them out - I have taken several out. I just haven't tried to clean them.
As for taking them out, you can lower the tank enough to get the sender out by running the nut to the end of the long bolt or all-thread. If you alternate between the two hanger straps you should be able to lower the tank even when it is pretty full.
As for taking them out, you can lower the tank enough to get the sender out by running the nut to the end of the long bolt or all-thread. If you alternate between the two hanger straps you should be able to lower the tank even when it is pretty full.
Elder User
Joined: Mar 2008
Posts: 509
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From: Central Florida
Where does the other end of the wire goto for the fuel level? Does it run directly into the back of your dash guages? I've got a brand new sending unit and gas gauge, but having the same issues as gimmeagig. 
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FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
Yes, if you have a single tank. With dual tanks it goes to a switch on the HVAC panel, which chooses which sending unit is connected to the gauge.
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Senior User
Joined: Jun 2013
Posts: 121
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From: Lake City, Florida
question: how do your other gauges work? I.E. the water temp gauge. I have an intermittent problem. sometimes my water temp gauge will show abnormally low (but normal range) and will cause my fuel gauge to drop more than what I know is in there. I hear there is a voltage regulator behind the instrument cluster that causes this. But if your water temp gauge stay in the middle or so and your fuel gauge is still wack...I'd agree about it being your sending units.
Mine is an 84 with two tanks as well
p.s. HVAC stands for Heating Ventilation And Cooling...it's how your turn your air on and there is a toggle switch to the right that controls your fuel tanks
Mine is an 84 with two tanks as well
p.s. HVAC stands for Heating Ventilation And Cooling...it's how your turn your air on and there is a toggle switch to the right that controls your fuel tanks
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5th Wheeling
Joined: Jun 2013
Posts: 35
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question: how do your other gauges work? I.E. the water temp gauge. I have an intermittent problem. sometimes my water temp gauge will show abnormally low (but normal range) and will cause my fuel gauge to drop more than what I know is in there. I hear there is a voltage regulator behind the instrument cluster that causes this. But if your water temp gauge stay in the middle or so and your fuel gauge is still wack...I'd agree about it being your sending units.
Mine is an 84 with two tanks as well
p.s. HVAC stands for Heating Ventilation And Cooling...it's how your turn your air on and there is a toggle switch to the right that controls your fuel tanks
Mine is an 84 with two tanks as well
p.s. HVAC stands for Heating Ventilation And Cooling...it's how your turn your air on and there is a toggle switch to the right that controls your fuel tanks
I just had the instrument panel out and i changed a bunch of bulbs cleaned contacts and painted it black. I hated this funky wood trim that had turned pink over time.
I'll be taking out the center panel too with the HVACc panel (thanks for explaining that for me). So I'll be cleaning all the contacts there. It would be nice if that's all it is.
I'll be taking out the Radio while I'm at it. It's really worhtless. A lot of the thrift stores around here sell units that are better than what I got. I just need one with a cassette player. I have one of those cassettes with a cable coming out of it that I use for my MP3 player. Much better than CDs.
Freshman User
Joined: Apr 2014
Posts: 41
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From: Canyon Lake, Ca
Hey there! New guy to the forums, and i know this is an old post but its why I am here. Im having the same problem. Did any of you find success with changing out the sending units? I feel like it might not be that problem with my truck because the gauge acts the exact same with both tanks, so I guess unless the sending units wore out in the same exact places it might be something else. Thoughts?
Its a 85 F250 with the 6.9. if that matters.
Its a 85 F250 with the 6.9. if that matters.
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
Pull the wire that goes to the sending unit and ground it. If your gauge goes to Full and stays when you wiggle wires then it is the sending units. And, it is very possible for two units to be bad in the middle.
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