Fuel sending unit only registers 1/4

[Jemo]

My project truck has been a project for 5 years and I took it out for the first drive tonight. I initially filled it with 5 gallons from the lawnmower container and drove it over to the gas station and filled it up. The initial rise to 1/4 tank made me think it was working but after the fill up, it didn't move. I bought the right sending unit for my gauges. Not understanding. Could it be because it sat for so long that the arm has stuck in place? I hate to drop the tank to figure this out!

[VetteVet]

Originally Posted by Jemo

My project truck has been a project for 5 years and I took it out for the first drive tonight. I initially filled it with 5 gallons from the lawnmower container and drove it over to the gas station and filled it up. The initial rise to 1/4 tank made me think it was working but after the fill up, it didn't move. I bought the right sending unit for my gauges. Not understanding. Could it be because it sat for so long that the arm has stuck in place? I hate to drop the tank to figure this out!

The fact that he arm had an initial rise to a 1/4 tank would seem to rule out that it was stuck in place.

Disconnect the fuel sender wire at the fuse panel and see if the gauge goes way past full with the key on. Then ground the terminal on the fuse panel and see if the gauge buries on empty. If it does then it indicates that the gauge is good. However it might do that and still have a bad resistor on the gauge itself.


connect a voltmeter to the sending wire and a good ground and read the ohms resistance on the sender. It should read around 30 ohms at 1/4 tank, with a full tank it should read 90 ohms. You might have a bad sender or the float might have a pinhole in it and the gas inside makes it too heavy to rise to full with the gas in the tank.

Here's a gauge resistance chart but the resistances do vary some between the years.




Here's a troubleshooting guide that specifically mentions the 1/4 tank reading.

[_Ogre]

do the above checks first, but since you've changed the sending unit...

my truk has the tank relocated under the bed, the vendor sent a universal sender
i had to cut and bend the sending unit to make it read the full range from E to F
i used a string thru a sending unit bolt hole to run the gauge up and down in the tank
that worked fine until i mounted the tank on the truck, now the float hits a baffle in the tank
it works fine from E to half tank, it's been that way for 5 years

stock tank or aftermarket tank?

[VetteVet]

Originally Posted by Jemo

My project truck has been a project for 5 years and I took it out for the first drive tonight. I initially filled it with 5 gallons from the lawnmower container and drove it over to the gas station and filled it up. The initial rise to 1/4 tank made me think it was working but after the fill up, it didn't move. I bought the right sending unit for my gauges. Not understanding. Could it be because it sat for so long that the arm has stuck in place? I hate to drop the tank to figure this out!

Originally Posted by _Ogre

do the above checks first, but since you've changed the sending unit...

my truk has the tank relocated under the bed, the vendor sent a universal sender
i had to cut and bend the sending unit to make it read the full range from E to F
i used a string thru a sending unit bolt hole to run the gauge up and down in the tank
that worked fine until i mounted the tank on the truck, now the float hits a baffle in the tank
it works fine from E to half tank, it's been that way for 5 years

stock tank or aftermarket tank?

A very important point Ogre