Fuel gauge problem

[wydomkr]

The 80 Scottsdale that I picked up a few weeks back, I have been going thru and fixing some of the little problems and I have one I need some input on.

It was on fumes when I picked it up, needle was below E. First stop was to the gas station. Put 10 gallons of gas in it and the needle just jumps all over the place. My first thought was the sending unit in the tank, but it does it when the truck is moving or just sitting. The truck doesn't even have to be running, you can just turn the key to the on position and it starts to move around.

Could it still be a sending unit issue? Possibly the gauge in the dash or a ground issue?

Will hopefully have pics up by this weekend, had to buy a new camera.

[Tony@AirRideTech]

sounds like the resistor in the guage itself..... easy item to replace.

[aero-pilot]

hmmm... Interesting. I have a fuel gauge problem as well. My fuel gauge only registers half a tank when it is full. It will never register a full tank, on either side I switch it too. It doesn't move around though it is stable.

Tony, what is this resistor you speak of?

[Tantrix]

Could be the sending unit...mine was doing the same thing but then after I couldn't get ahold of a fuel tank without pinholes rusted in it, I ordered a new fuel tank from RockAuto. While I was at it, I went ahead and got the sending unit with it too.

Fuel Tank $78.79
Fuel Tank Sending Unit $46.79

Installed both and no issues from fuel gauge after that. Matter of fact, it's dead-on accurate. I ran my truck (20 gallon tank) to 1/4 tank according to the gauge, and when I filled up, could only get 15 gallons in.

[ron350]

The gas gauge in my 75 C-10 has an 82-ohm ceramic resistor bolted across two bolts on the backside. Wonder if this resistor has a different value on different models?

There are three pins (bolts) located at 9 o’clock, 3 o’clock, and 6 o’clock on the backside of the gauge.
With the 82-ohm resistor in place the resistance of the gauge reads.
9 pin to 3 pin = 42 ohms
3 pin to 6 pin = 145 ohms
6 pin to 9 pin =104 ohms

Resistance with the resistor removed reads.
9 pin to 3 pin = 85 ohms
3 pin to 6 pin = 188 ohms
6 pin to 9 pin =104 ohms

[aero-pilot]

Tantrix, are you referring to my issue or wydomkr? Or Both?

[Tantrix]

Originally Posted by aero-pilot

Tantrix, are you referring to my issue or wydomkr? Or Both?

Sorry, I was referring to wydomkr.


I'm assuming you have 2 tanks on yours since you said:

It will never register a full tank, on either side I switch it too.

In that case, you have 2 seperate sending units...one in each tank. Your problem is probably the gauge itself (and a less expensive fix) rather than 2 bad sending units. I'd try another gauge from a wrecking yard, or better yet...try ron350's test and see what you come up with on your gauge first. If you try another gauge and it does the same thing, trace your wiring from the gauge, under the chassis, all the way to your tanks and make sure you have no breaks in it. The chances of you having 2 bad sending units is slim (but not impossible of course).

[aero-pilot]

Originally Posted by Tantrix

The chances of you having 2 bad sending units is slim (but not impossible of course).

Yeah that's true. Thanks for the advice!

[wydomkr]

Thanks for the advise and suggestions, I bought another gauge cluster, so I guess I'll try the dash gauge first and see what that does and then move on the the tank sender.

[BigE77']

Sorry to kind of bring up an old one, Having problems with my fuel guage, it reads way past Full all the time and when I shut if off it goes back to E, if I just turn the key on it runs right back up to way past full.....any thoughts?