86 F-250 460 dual tanks, rear gauge does not work most of time but sometimes if I get on a rough road or hit a bump fairly hard the gauge will start working. Everything else works fine, when I flip switch it will pull fuel out of rear tank the gauge just doesn't work most of time. Gauge works fine on front tank. Any chance this is a common problem


Thanks

 

Since your problem is intermittent it may be harder to find. But this is a common problem, and 99% of the time the sending unit in the tank is the problem.

There can be other problems, but that's the most common problem area, they just did not make them very well during this time period, and they wear out. The old sending units had wire wound resistors in them, these units used "painted on" resistance material, and it wears off over time.

 

Sending unit. You can test the electrical and gauge by unplugging the tank wiring, turning the key to on and grounding the ground wire to metal. If all is good it will peg the gauge to full. Then you know it's the sending unit for sure. You can also use this method on the coolant temp switches and stuff like that as well to test.

 

Thanks for the info guy's, I knew about the grounding thing and making the gauge peg full. I was already sure it was the sending unit but just wanted some expert advice to confirm. The bad part is this is one of them 460's truck that has the electric pumps in the tank so I am assuming the pump and sending unit are all one piece. Which I am also assuming means $$$...again thanks for the info.

 

They used to sell the sending unit with or without the pump. I haven't looked lately though.