Ford 4x4

I have a 85 ford with the 300 6. It has one tank, which is the front. The fuel gauge does not read the gas that is in the tank, i dumped about 10 gallons in it and the gauge stays pinned at empty.

Is this a sending unit problem, or should I look for disconnected wires or a faulty gauge first? The Previous owner installed an aftermarket oil pressure gauge, so could he have accidently disconnected the wires for the fuel?

Btw all the other gauges in the truck work fine, just the fuel gauge.

Thanks ahead of time!

klricks

A problem anywhere in the fuel system from gauge to sender could cause the same issues.
It's not possible for you, me or anyone else to know which it is without doing some diagnostic work.
1st thing to do is pull the connector off of the tank. Short the 2 pins of the cable together with a small jumper wire. The gauge should 'peg' full.
(Don't leave the jumper on for a long time).
If that works it's most likely the sender.
If gauge does not respond then start looking at wiring including grounding from there back to the fuel gauge etc.

Here is a diagram of the fuel gauge circuits.. (From '86 manual):
http://imageshack.us/a/img507/4813/solsel.jpg

It's possible that the PO hacked the fuel gauge out of the circuit. You will have to compare what you have to the above diagram in order to figure it out.
Is the original oil pressure gauge and sender still present and functional? If not that would throw off the other 2 gauges fuel and coolant temp.

Ford 4x4

The factory oil gauge works fine, as well as the speedo, the temp gauge, and the voltage gauge. The only one that doesnt work is the fuel gauge.

For the test to see if the gauge works, (the wire bypass) i have to have the truck running correct?

klricks

The engine does not need to be running. The ignition must be turned to ON or ACC position.

Ford 4x4

Alright, thanks alot, ill hopefully try the test tomorrow. I plan on doing frame off restoration on it, so if its the sending unit it wont get fixed for a little while yet.

MonkeyWrench

I know this thread is old and all but you don't have the page that shows the grounds to go with that diagram would you Klricks? If so I would highly appreciate it. I keep running out of gas because of no fuel gauge and my mpgs are never the same I am currently working on fixing that but until then I. Just wanna get my gauge working so I can know for sure what's in the tank.

klricks

Diagram:
http://imageshack.com/a/img850/9286/grounds.jpg

Locations of splice connections and grounds:
http://imageshack.com/a/img138/2906/ground1s.jpg
http://imageshack.com/a/img222/6159/ground2.jpg

Half ton

I just wanted to say thank you for that test information. I have a 1982 F-150 5.0 v8 and my rear tank doesn not registar on the gauge cluster only the front tank so i am going to try that pin test. I thought i would also follow the wires from the tank top forward to make sure no broken wires and just for education sake.

MonkeyWrench

I tested my sending unit by jumping the wires together and it pegged full after always reading empty. So just so I got this right this is a faulty sending unit correct?

klricks

Yes it could be the electrical part of the sender or maybe the float has a hole in it and is saturated.