Fuel gauge doesn't work in 68 Road Runner

[moparmusclecars]

I'm terrible at wiring. Can you guys please advise me on checking fuel tank sending unit, etc? How would I check the connection at the sending unit, and then the gauge? Can I check these two without pulling the tank and sending unit at this point? If i need to buy a new sending unit, where is the best place to get one that is actually accurate? I appreciate any and all help! Thanks!

 

[69a100]

Have you done anything to the system to cause this to happen? The first thing to check is the ground strap, is it there? It jumps the piece of rubber between the sending unit and the line to the pump. Is the fuel line clean/un-rusted, same with the ground strap? Is it on there tightly? Is the plug at the sending unit rusted or in bad shape?

 

[moparmusclecars]

Bought car a few years ago with new tank installed and the gas gauge has never worked since I owned the car. I'll look at the ground strap for starters. Fuel line brand new, when rebuilt engine was installed. Any other advice would be appreciated!

 

[uranium238]

You can get a wiring diagram at this page, if that'll help:
http://www.mymopar.com/index.php?pid=24

There should be a ground from the tank to the body, but the gauge should work sometimes if it was just an intermittent ground.

The sending unit has a float on the end of it like in a carb. If the old unit was just re-used, that float may be bad.

- - - Updated - - -

Have you done anything to the system to cause this to happen? The first thing to check is the ground strap, is it there? It jumps the piece of rubber between the sending unit and the line to the pump. Is the fuel line clean/un-rusted, same with the ground strap? Is it on there tightly? Is the plug at the sending unit rusted or in bad shape?

Sorry, just noticed you already mentioned the ground. It's always the first thing I look for.

 

[1968RRTEXAS]

What did you find?

 

[Cornpatch MO]

I attached my sender ground to the body. The factory had a jumper ground to bypass the rubber hose between the sender and the fuel line. But the stock fuel line was steel all the way to the fuel pump. Chances are you now have another rubber hose from the fuel line to the pump = no ground unless it grounds thru the fuel line body clips,,,,,,,,,,,,,,,,,,,,,,MO

 

[miller]

no ground unless it grounds thru the fuel line body clips

One other thing you might look for...how the steel fuel line runs, just off the sending unit. Line normally bends up going to the underbody, and on from there. On my 64, where the fuel line attaches at the body, an all steel clamp fastens it there, making a positive ground to the body.

 

[bigmanjbmopar]

Did you ever get it fixed?

 

[Dennis H]

He hasn't had enough years to read all the other fuel gauge doesn't work threads. Mine was in need of a separate ground.

 

[1968RRTEXAS]

Mines has no ground. So I will have to ground it.

 

[Cornpatch MO]

Mines has no ground. So I will have to ground it.

View attachment 346772

Mine was just like yours with no ground. I pulled my rubber hose and mini clamp off, just far enough to get another mini clamp in front of it on the bare outlet pipe. I put a wire under that hose clamp and ran the other end to a ground. Cleaned off a bare spot on the under body , just a few inches away and put a self tapping screw into a wiring end eye. .................................MO

 

[1968RRTEXAS]

Mine was just like yours with no ground. I pulled my rubber hose and mini clamp off, just far enough to get another mini clamp in front of it on the bare outlet pipe. I put a wire under that hose clamp and ran the other end to a ground. Cleaned off a bare spot on the under body , just a few inches away and put a self tapping screw into a wiring end eye. .................................MO

I finally got under the car this weekend. I pulled the sending unit wire off and grounded it....turn the ignition key on and the fuel gauge went to full! Good News

I replicated what you did with your grounding wire...self tapping screw..wire under 2nd mini clamp. Got out all excited, turn the ignition on, and the fuel gauge went to..drum roll....it went up to E! The tank is at least 3/4 full. Its a new sending unit. Any ideas on what i should try next?

 

[bigmanjbmopar]

It has to be the grounding if the guage went full by grounding the sender lead then it is the sending unit amd th metal its made out of. Is there any way your tank is somehow isolated from the body of the car even if just slightly? The sending unit needs to be in contact with the body of the car just like any other device in the car. Can you take a piece of copper wire and physically secure it to the sending unit wither the tube or the body and then to a know good ground on the car then turn the key on? I think your tank or sending unit is just not making good ground contact.

 

[1968RRTEXAS]

It has to be the grounding if the guage went full by grounding the sender lead then it is the sending unit amd th metal its made out of. Is there any way your tank is somehow isolated from the body of the car even if just slightly? The sending unit needs to be in contact with the body of the car just like any other device in the car. Can you take a piece of copper wire and physically secure it to the sending unit wither the tube or the body and then to a know good ground on the car then turn the key on? I think your tank or sending unit is just not making good ground contact.

The ground wire I made is good to the body. The way it's grounded to the sending unit supply tube isn't great. Does it have to be grounded to the sending unit or can I ground it to the tank. I know there is a rubber washer behind the sending unit

 

[bigmanjbmopar]

Unit, and make it as good of a connection as possible, fyi stainless steel sometimes is not great at conducting a ground, light sanding on the area may help.

The factory ground strap as you know wrapped around the tube and the 5/16" line after the rubber hose section, is yours rubber all the way to the pump?

 

[Cornpatch MO]

I finally got under the car this weekend. I pulled the sending unit wire off and grounded it....turn the ignition key on and the fuel gauge went to full! Good News

I replicated what you did with your grounding wire...self tapping screw..wire under 2nd mini clamp. Got out all excited, turn the ignition on, and the fuel gauge went to..drum roll....it went up to E! The tank is at least 3/4 full. Its a new sending unit. Any ideas on what i should try next?

Since it moved up to E, I believe your sending unit is working. If your sending unit was out, so you could move the float, you would have a range of 10 to 74 ohms. Is it possible to have the sending unit in upside down? You may have to take the sending unit out and manually move the float and observe the gas guage .................................MO

 

[1968RRTEXAS]

Unit, and make it as good of a connection as possible, fyi stainless steel sometimes is not great at conducting a ground, light sanding on the area may help.

The factory ground strap as you know wrapped around the tube and the 5/16" line after the rubber hose section, is yours rubber all the way to the pump?

Good ideas. I will take what I have off and put some sandpaper to ensure the best ground connection possible. I have steel line front to back with just short pieces of rubber to attach the tank and fuel pump.

 

[1968RRTEXAS]

Since it moved up to E, I believe your sending unit is working. If your sending unit was out, so you could move the float, you would have a range of 10 to 74 ohms. Is it possible to have the sending unit in upside down? You may have to take the sending unit out and manually move the float and observe the gas guage .................................MO

Due to the shape of the sending unit. I don't believe it's possible to installe them upside down. I put the sending unit in myself and remember operating the float by hand prior to install so I would know it's installed correctly.

 

[kiwigtx]

I had this once - turn the key on and the gauge went to 'E' - turned out to be a pinhole in the brass float, and it was full of gas. Changed the float and all good again.
Inquiring minds need to know if @moparmusclecars ever got a fix on his '68 RR

 

[RobP]

I'm having the same issue except my gauge will go up to about 1/2 when it's closer to full. Grounding the lead wire will peg the gauge at full. I didn't have the ground strap and made my own which improved the reading from 1/4 to 1/2 tank, but it's still not correct. I may try a new fuel sender.
Let us know how you made out.