fuel guage is wonky

[carpenter_jai]

This was a problem about 5 years ago that went away on it's own, and just came back. Lately, my fuel guage has been acting a little possed. Fueled up today, it read 5/8, drove around all day, then it read 7/8. Last week, it went from about 1/4 to 3/4, and everything in between. Normally I would be happy to see my guage go up without stopping at the gas station, but wishing it was magically filling is not the same as the real thing. Anybody know what does this? It's a 95' 3 banger.

Jai

[vcrmonthly]

You could be experiencing the same thing that I pulled on my wife when she owned an '88 sprint. She was regularly getting 48 mpg and bragged about it a lot. I decided to bug her and started sneaking out at night and putting extra gas in her tank. I started with just a half gallon. Then I progressively worked it up to about 2 1/2 gallons. She finally got suspicious when her mileage increased to 77 mpg. I gradually decreased what I was putting in her tank until it was nothing extra. I thought of siphoning out gas, but that seemed like to much trouble for a practical joke. It was only about 2 or 3 years later that I came clean with her and told her what I had done. At first she was a little "miffed" at me, but then we both had a good laugh over it. We never should have gotten rid of that car.

[MatLax]

The fuel gauge were never really good on those cars and a small change in inclination will make it move alot, but from ¼ to ¾ that would be a first...

[carpenter_jai]

Ha! good story vcrmonthly! Since I regularly calculate my mileage, I know that no ones adding gas to my car, but I wouldn't mind. As far as inclination goes, yeah I know about that. I live in a pretty flat city, and I have been comparing the guage readings on flat surfaces only. Is there a floating device in the fuel tank or something? How do these things work? What can go wrong with them that it would get all weird for a while and then go back to normal for 3 years before getting screwy again?

Jai

[hot_sd]

Yes, there is a float that goes up and down with the fuel level inside the tank. The slider forms a variable resistor. The voltage drop across the resistor is measured as fuel quantity by the gauge. The slide can get sticky after a while and does not move smoothly - if it gets stuck and then moves you could be seeing these jumps.

A quick check would be to disconnect the sender wires and stick a fixed resistor between the wire terminal and drive around for a while. If it remains steady then it is the sender - if it continues to do it it could be loose wiring or the gauge itself. There is an expensive test box from kent moore that the techs use but you can just buy a couple of fixed value resistors from Radio Shack and do the experiment. Accoring to my manual - about 10 ohms should be a full tank and above 120 ohms should be reading empty. You can try 10ohms, 120 ohms and another value for half tank - like 50 or 60 ohms ( or whatever the nearest preferred value is available).

My gauge is underreading so I guess I will need to replace the sender when I replace the filter sometime next year. Not looking forward to this as the tank has to be removed.

[carpenter_jai]

Crap... or I could just refill every 500 km...

Jai