Hey guys. The fuel guage on my 86 is not working. I have dual tanks on a long bed. Both tanks work but neither will register on the fuel guage. I know it could be both gas tank sending units bad, but i'm wondering if there might be anything else that I should check before I drop the tanks out and replace the sending units?

 

Could be a number of things. If you know how to use a volt/ohm meter then you should be able to find the problem by testing at the dash tank select switch.

Could be the senders or fuel selector switch on the dash or could be a problem in the dash gauge circuit or any wires between.

If you have the electric tank switch valve, down on the drivers side frame rail, then there could be a problem with that as well. If you have the non electric tank valve selector then the tank sending wires go directly to the dash switch.

Get at your dash fuel selector switch and pull the connector.
Test the switch. If OK then measure ohms to ground for each tank sending wire. Should have a few ohms depending on the fuel level.

With ignition key on, measure the DC voltage on the gauge wire to ground. On my 86 F150 that wire pulses on and off every few seconds. If nothing then there is a problem in the dash.

Where to get sending units you ask? I have seen them online at Napa and Autozone etc but have not tried to order one yet. There are different models depending on tank size... 19 gal. or 16 gal.... side tanks or center tanks... all are different.
I have a problem with no flow from my rear tank and I am in the process of fixing that. I am replacing my tank selector valve 1st.

I have the factory wiring diagrams for 86 F150. If you need more help let me know what exact model/ engine you have etc. and I can look things up.

Kevin

 

Hey thanks. I appreciate the info. I will be checking this out.

 

I have a 2006 ford f-150 my fuel hand isn't working I have had the fuel gauge sending unit replaced and still nothing

 

Back in my day, we would adjust the gauges by using a rheostat to adjust the resistance of the circuit. Dial in zero resistance and the gauge would read either zero or max. (no memory). Again dial in say 86 and gauge would be at oposite. What I am trying to say is the gauge should respond to either an open circuit or a shorted circuit. You guys with one gauge for two tanks, check the gauge first. Go with the odds.

 

I doubt you have a bad gauge since the fuel gauge in you truck is usually serviced as part of a new cluster. I would just grab a basic wiring diagram for your truck for the fuel pump, go under the truck and find the harness that runs to the fuel pump. Check the correct colored wire for the gauge and check the ground signal running to the cluster. It will likely be a bad sending unit inside the tank. All auto manufactures, especially Ford had a lot of issues with sulfer contamination in the fuel causing build up on the needle on the sender inside the tank on the pump. The solution for this was replacement of the fuel pump sending unit. Without a doubt verify the cause of your issue before replacing parts. Sometimes its best to have an ASE technician at a shop diagnose the problem first if you cannot yourself.

 

i have i 87 f 150 and one of the tanks register but the other one wont till i get to about 1/4 of a tank

 

Probably need a new sender unit in that tank.
In the sender there is a rheostat like wiper which moves across a resistance wire pattern on a circuit card. A float and pivot mechanism moves the wiper across the resistor wire changing the resistance as the level of the fuel changes. A portion of the card is probably covered with varnish or tar like gunk or the wiper arm is bent.

I had a bad sender on my '86 and was going to attempt to repair it but there was so much gunk and rust in the tank that gave up and just replaced both the tank and sender.
Tank was $100.00 US and the sender with pump was $120.00 at Autozone.
Kevin

 

o ok thanks i will look in that

 

could be a pin hole in the float....as the last result. My old EB acted crazy like this.