Fuel gauge doesn't work in 68 Road Runner

Update: sanded the stainless steel line. Re-installed my ground. No change. Pulled the sending unit out. Verified it was installed correctly.(fuel supply on left, sending terminal on right). Submerged the sending unit in a big bucket of water, no bubbles from the float. Ohm testing revealed

7.7ohms empty
84ohms full

Re installed it all. Did a better ground IMO. OHM tested revealed 52.7 ohms installed. Fuel gauge still sitting on E......

What's next lmao

Have your replace the wire from the sending unit to the cluster? it could be pinched and grounded somewhere maybe at the aft bulkhead connector. You can pull it off at either end and take both an ohm reading to ground which should be virtually zero but if its not and its shows .01 or depending on your meter 00 OL or 000 could be a dead short to ground or if it reads 10,000 ohms or more could be just touching somewhere maybe rubbed on something along the drivers side somewhere where it runs. If its not the wire or you have already ready run a new one then the only other suggestion I know of is the gauge is self, it is adjustable and was calibrated at the factory originally, and can be adjusted or more or less empty or full readings I have done few times, its a little know or understood item always overlooked, but on the back of the gauge on the left and the right are little windows inside are gogs you can kick one of the gears of the gog down or up to adjust the needle position and when tested on a bench can be calibrated to where you want it / should be. Most just give up and buy a new one lol

The resistance range of the sender unit is wider than what gauge can indicate.

What normally happens is that even if you fill up the tank to the full the gauge will not point all the way to the full level and by the time the tank is 1/2 full or even 3/4 full the gauge shows empty which can be a bit of pain.

Commonly used configuration is that when the fuel level is full the resistance will be low and resistance value increases as fuel level decreases in the tank. If the gauge read out range for example is between 80ohm to 10 Ohm then when the tank is 2/3 full with 260 - 20 Ohm sender range the gauge will read empty even though the tank is 2/3 full.

I have one of the Repop senders that never worked, all wiring is good and the gauge will move from e to full when grounding Ect. I pulled the filler neck and used some long 3/8 fuel line to jostle the float and arm around. Guess it was just sticking in the sender body,now Iget a full tank reading and a empty reading as it should be. When it is at a 1/4 tank reading I fill it and only can get about 9 gallons in it. Guess I have a 10 gallon reserve LOL.

Back at it again. Going to try this grounding strap. FYSA it's only $9. Will post update later.

wagonman said:

I have one of the Repop senders that never worked, all wiring is good and the gauge will move from e to full when grounding Ect. I pulled the filler neck and used some long 3/8 fuel line to jostle the float and arm around. Guess it was just sticking in the sender body,now Iget a full tank reading and a empty reading as it should be. When it is at a 1/4 tank reading I fill it and only can get about 9 gallons in it. Guess I have a 10 gallon reserve LOL.

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Install a meter match kit and you can recalibrate the gauge so it will be accurate. http://www.technoversions.com/MeterMatchHome.html

well as the clock strikes midnight, no luck. tomorrow im going to try and manually lift up the float to see if it reads anything. (like wagonman)

If it works right out of the tank then its working. Something is blocking the grounding after its installed you need to figure that out. In a previous picture it looks like you whole tank is black? Is it black where the unit sits in the tank? Maybe the painted surface is not helping?

bigmanjbmopar said:

If it works right out of the tank then its working. Something is blocking the grounding after its installed you need to figure that out. In a previous picture it looks like you whole tank is black? Is it black where the unit sits in the tank? Maybe the painted surface is not helping?

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My whole tank is black. The tank itself it's t grounded to the sending unit be design, due to the rubber washer seal that goes between the sending unit and the tank. But I'm with you. If the sending unit works out of the tank. And the gauge is moving when grounded. Then it's most likely a ground issue

1968RRTEXAS said:

My whole tank is black. The tank itself it's t grounded to the sending unit be design, due to the rubber washer seal that goes between the sending unit and the tank. But I'm with you. If the sending unit works out of the tank. And the gauge is moving when grounded. Then it's most likely a ground issue

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The sending unit would be grounded to the tank thru the mounting screws, even tho there is a rubber washer-gasket....................MO

J hook screws and straps of the same type of metal, his looks like its was sprayed with undercoating or something?

bigmanjbmopar said:

J hook screws and straps of the same type of metal, his looks like its was sprayed with undercoating or something?

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I don't think the gas tank itself has to necessarily be grounded, but the sending unit has to be somehow grounded through the steel outlet tube..........MO

Today on Mopar garage. I removed the filler neck and got a good pic of the float as it sits now with the reading at E. I used a wire and lifter the float all the way up and my fuel gauge reads 1/2. So do I replace the sending unit or try the adjustment bigmanjb Mopar suggested.

Well that plastic float is junk hope you got a brass one with the new unit

I might be a little lost on this one but, here's what I see:
- the float is floating - not junk. It looked like it was on top of the fuel in the first picture.
- the sending unit out of the car has the correct ohm readings.

When you tested today, what was your ohm readings? If you lift the the float all the way up and you get the right ohm reading then it's good. Same with the 1/2 tank reading. Test at the sender first using the sender as the ground source, the move to the body. If both readings are the same, move on.

I would be moving up to the dash if all that works out. Find the wire at the dash and take the same ohm reading using the body of the car as you ground.

Its junk i will get a hole in it sooner than later. It may be working now but all this trouble shooting to get it fixed just to have it tank over a piece of plastic would be shame, the suggestion is to replace it now with the know OE brass one that is sealed. The arm on the unit probably just needs to be bent its likely not going to the full mark on the rheostat when the tank is full.