innaccurate fuel gauge

[kassim503]

My car's fuel gauge goes up past full when the tank is full and when the tank is empty it reads something around 1/6 tank.
Whats making it do that? Ive been driving with it for so long that I have grown used to it, but if there is a easy fix I would like to fix it

[asavage]

I just spent some time with the FSMs, and I am leaning to a faulty fuel gauge. However . . . this isn't as straightforward to guess at as you might think.

According to your clock post and pics, you have an SL model, which has the oil pressure and voltmeter gauges (as well as a tach). We diesel folks don't have that option, and the non-SL gassers don't have them either.

The SL instrument cluster has two mechanical heated/bimetal-type voltage regulators. On yours, one feeds the Temp gauge, the other feeds both the Fuel Level gauge and Oil Pressure gauges.

If the oil pressure reads marginally high as well as the fuel level, then you can tweak the mechanical voltage regulator, screw its screw in a little bit to reduce the ON time of the contacts. Here's a pic of the voltage regulator in my '83 Wagon:

(click on any image for larger)


See the screw? It can be adjusted within a limited range. It requires a jeweler's screwdriver, you're not going to adjust this with a 00 flatedge. Maybe with a broken-off razor blade, I've done that before. But it's a reach.

On your SL cluster, this adjustment will affect both the Oil Pressure readings and the Fuel Level readings. That might not bother you, but they're both going to go down together.

Or, you could swap the gauges out. If they're like mine, they are really one unit. While I could separate mine from each other, I doubt that I could get them back together and working. Carimbo has a spare SL cluster, you might ask him nicely if he would part with those two gauges.

The other possibility is that you have a small electrical "leak" (short) to ground on the wire that runs from the gauge to the sending unit. The most likely area for this to occur is wet mud & crap on top of the sending unit. This is easy to check: remove trunk mat, remove sending unit cover (three screws, I think), and look down. If there's only dust there, go back to the gauges. If there's a pile of mud and such, then note the current fuel gauge reading, hose down the top of the sending unit and let it dry off, check the fuel gauge and see if the gauge moved down.

[kassim503]

mud on contacts huh? 95% chance there is going to be mud caked all over there, this car sees more off roading than paved road. Ill check her up tommorow.