Hi all fellow Ford lovers. Hate to ask a question that has been covered so much but can't find the answer.

Filled up my F250's front tank all the way(did not top it off I never do), and put $10 bucks in the back tank. After driving around town about 60 miles the gauge still didn't move from full. I switched to the back tank to see if the gauge was working and it stayed pegged at full. Over the course of the last two weeks its slowly dropped to just below 1/4 tank where it has stayed after filling her up a few more times. I read that pegged full is a bad ground but pegging full then dropping?

Bad ground? Bad switch? Blown fuse? could it be a bad connection on the frame somewhere?

As always thank you for your expert Ford 9th Gen F Series advice!

 

There could be a couple different problems I think.. If it only does it on one tank, the one problem could be a bad fuel measuring device (I forgot the name) that is attached to the fuel pump inside the tank. Another problem could be the connections, I would check the ground and make sure there aren't bad connections. And another problem, I think this might be it, but a bad fuel sending unit. If it was a bad fuse, the fuel gauge wouldn't be working at all, so rule that one out.

I'm not exactly sure on the answer so don't quote me on it, but I hope this helps.

 

I bet it's the sending unit too. It's located in the tank from my understanding. Dropping the bed makes it easier to replace.

 

Ya I think it's the sending unit. It is located on the fuel pump inside the tank and taking the bed off does make it a lot easier, as long as the bed bolts aren't rusted like mine are. If they are, you'll have to drop the tank on a jack and remove all the connections from underneath. To do that, you'll need the quick disconnect fuel line tool from Advance for like $7 I think and it's metal. The measurements for the fuel lines, if it's unleaded gas, are 5/16 and 3/8 and those are3 the measurements on the tool. There's 2 fuel lines to disconnect, then there's an electrical connection that you'll have to disconnect, and finally the emissions line that should just pull right off, and if not just stick a screwdriver inside it and pry it off cause sometimes they get stuck. After that, take out the gas filling hose and it should just drop. After that, take off the lock ring and pull out the fuel pump and replace the sending unit and just do everything I said, but in reverse. Hopefully that fixes the problem.

 

Don't think it's the sending unit as the gauge doesn't work on either tank - I first thought that was the issue. The gauge doesn't work at all and is staying in the same spot, I don't think it's a fuse because that is the only thing not working in the cluster and all lights interior/exterior are in working order.

I read on one post that there is a plug/connector on the frame kind of under the drivers seat but don't know what it looks like.

Do both tanks sending units connect to a central plug/connection and run to the engine bay?

The reason I'm not sure if it's a bad ground is because it moved, I read that a bad ground it will peg and so when it slowly moved I wasn't sure if that was it.

 

If you have 2 tanks then yes, there is a fuel tank selector valve (I believe that's what it is called) that sends the fuel to the engine from whichever tank you have the switch on. Its inside the rail underneath the rear of the cab and those go bad sometimes, especially on OBS Ford's, so that might need replacing so I'd check that. But I didn't think that it would cause your gauge to act like it is, but I'd look into it if I were you.

 

I'm in the process of replacing my fuel pump and sending unit and I actually made better time dropping the tank. It's only 4 bolts holding the tank straps. And all you need is a pair of needle nose pliers to remove th clips. No special tool needed. Mine reads full constantly and my in tank pump sounds like grinding metal and gravel. Just remove the filler neck and fuel lines. Then slowly lower the tank with a jack. Took me a couple hours. I started by pulling the bed but one of the bolts was already rounded off .

 

It's probably stuck b/c the sending unit in that tank is bad. it's stuck at whatever it was at when the unit stopped working. Just a thought, not a for sure answer

 

Spent a few hours troubleshooting this and still can't figure it out. Does anyone know where the ground is for the fuel tanks? I read that it's around the radiator and didn't see any wire hooked to the radiator, core support, or frame in that area. I checked every fuse and found one that had no juice to either side, it's a 4 amp fuse.

Looking under the truck and following the wiring from the rear tank past the fuel filter I didn't see any fuel selector switch. I know both pumps are working because I ran out of gas on the front while driving and switched to the back and kept going on my way. I'm stumped, if both pumps are working and both tanks are operating, if the switch inside the truck is working why in the world does everything work except for the gauge!

 

what year and model truck are you working on?
the tank is grounded to the frame by a small wire off the sending unit usually..

 

1997 F250 HD with the 5.8L and E4OD.

 

Fuel pump, selector, gauge circuit diagram:


Ground G100 location:


Your 5.8L equipped truck has the same ground location as the above.

The Fuel Tank Selector switch is located on the dash of the truck. It has two sets of contacts, one for the pump, the other for the respective fuel sender.

 

Thank you for the diagrams I know exactly where G100 is but I didn't think the ground would come all that way and not start at the rear of the truck.

I can get another switch on the inside of the truck, I know that they can go bad but wasn't sure if part of the functions of the switch could go bad or if the whole switch would go bad.

 

There are several wires that go to G100 as you probably saw. It does seem odd Ford used a ground at the front of the truck for the fuel tank operation. I guess they knew that steel is not as good of a conductor as copper.

 

Ok I hate to kick this can down the road again but I ran out of gas again yesterday and I need to fix this. So far I've changed the switch inside the truck, removed the bolt on the G100 ground and took a wire brush and sand paper and made it shine and both have not fixed this issue. I went to the yard and got another cluster with a tach from a March 1996 F250 that I'm going to install this weekend.

Any other ideas?