Gas gauge sticks

[Grandmashotrod]

Aparently my gas gauge sticks because I'm on the side of the road with "half a tank". How can I fix this?

[BerniniCaCO3]

We need you to gather more information

It's a simple system. Float on the sending unit in the tank floats up and down with fuel level. It's attached to a variable resistor. There's a base signal voltage, I'm not sure it's 12V in fact I think it might be 7 or 8V (but I'd better check), which gets eaten in part by the resistor. The remaining voltage goes through the instrument cluster gauge, and the current runs through a coil that affects a magnet on the needle, pulling it to one side. It either resists a spring, or, opposing coils that generate a magnetic pull the other direction.

First, what year? There are little changes in how they did the gauge; 1990 vs 1989 was a big change (1990-93 has an antislosh module, and the resistance values sent from the sending unit are completely different from the 1989 and earlier models). I'm not sure if between 1985 and 1986 there were other big changes.

Find out what it is doing.
Fill it up completely. Does it show completely full? Or does it show waaaaaay overfull, more than it used to? Or is it always on half a tank, all the time, no matter how much fuel you have left?
This will help a lot.

1990-1993 has high resistance equating to a full tank, so if you have such a model, then very high internal resistance would result in a gauge that shows, say, 1/2 full, to really, very overfull. That resistance could be anywhere in the wiring and you'd have to do some checking with an ohmeter.
If you have 1986-1989, then high resistance is empty, and low resistance is full. Nothing really results in low resistance, unless somehow the variable resistor in the sending unit was circumvented, and I think that unlikely to impossible.

I've heard of floats getting caught on wiring, but I don't think that's an issue in the way our sending units are designed. I work on volvos, and there's 3 feet of wiring in the tank, and the float can get tangled in it (some models anyway, to qualify)
That would prevent it from showing less than a certain amount full, as the float bottomed out on some obstruction, the wiring, namely.
There could be an internal fault in the gauge, with the needle getting physically stuck on something. I know my own needle defaults to 1/2 tank when you shut the care off, but i"m told that's not right. My own needle also never showed MORE than 3/4 full, so there was more than that wrong, and that was with my gauge. I bought a used instrument cluster to fix it. I have a 1990. One of these days I'll take the fuel gauge apart on a bench and see how it ticks, internally, and see how it might be repaired.

[86VickyLX]

does the fuel pump work?

[BerniniCaCO3]

whoops, good question 86Vicky, I just assumed it was his fuel level sensing system.
Do you have half a tank and the gauge is quite accurate, and no fuel going to the engine for some other reason?

There's an inertial switch too, that shuts off the fuel pressure in the event of an accident (when the inertia of the car would change rapidly!).
Maybe it got tripped.
Maybe it's failed, and trips too easily.

As for the pump, it's a subtle sound, and I didn't used to pick up on it although I can hear it now: but when you turn the car "on" (all the dash lights on, but you haven't actually cranked it yet), at that moment, you hear a short, quiet buzz as the pump primes the fuel system with pressure, getting ready to start the engine. If you don't hear that at all, maybe the pump is dead.

[bigbeigeboat]

Aparently my gas gauge sticks because I'm on the side of the road with "half a tank". How can I fix this?

fill the other half



If its not a fuel pump, inertia stitch, fuel pump relay or fuse. and it really is sticking at 1/2 (rare as the usually sink or sick at empty from sitting a long time.
get a bottle of drygas, a bottle of oily carb/injector cleaner and dump them in the tank with 1/8-1/4 tank of gas. then go back and forth over a tall speedbump 9-10 times.

[86VickyLX]

I've also seen where the gauges get stuck if people touch them. 89 and down fuel gauges don't like to be touched...

[Grandmashotrod]

89 Marquis
fuel pump works
has always gone an 1/8th past full but the last week at half a tank it's empty but still fills up to the original position. I'll give some cleaner a try