Fuel gauge/sender problems- reads half when really at empty.

[Guest Anonymous]

I don't know how to fix this, but my fuel gauge reads at about half when the tank is empty. Anyone else had similar to this? I know these gauges seem to do lots of odd things, but I don't recall seeing this happen before. Any suggestions on how to fix it? I also have a tachometer problem, it doesn't seem to work at all, what things should I check other than the wire at the coil? TIA.

[Guest Anonymous]

When did these gauge problems develop? For example, have your gauges always been like this or did these problems begin when you had other things going on with the car?

The most obvious thing to check for a tach problem is to make sure that the sensor wire (black wire) is in circuit on the negative side of the coil (it is usually physically attached at the distributor).

For the gas gauge, does it read OK at any point in its range? For example, does it ever read above half full? Your float could be sticking. You may have to pull your sender to see what is happening.

Chris B.

'73 ex-Malaga

[Guest Anonymous]

I'll check on the negative hookup again for the tach. As for the fuel gauge it reads full when the tank is less than half full (not sure how ful it really is) and progresses down to about half way which is where it stops and I'm out of gas. So from that I think the float is working fine, but maybe there's some bridge between the two wires (it's a '72). I've pulled it out plenty of times and haven't been able to see any problems.

[Guest Anonymous]

I'll check on the negative hookup again for the tach. As for the fuel gauge it reads full when the tank is less than half full (not sure how ful it really is) and progresses down to about half way which is where it stops and I'm out of gas. So from that I think the float is working fine, but maybe there's some bridge between the two wires (it's a '72). I've pulled it out plenty of times and haven't been able to see any problems. Oh, and they started after I messed with the sender the first time- it was reading at the top always (after it was parked outside for about 7 years) and I thought it was working right, but apparently not (I found out the hard way). Does the gauge have to be put in with the tank empty, or have the wires hooked up when the float is at the bottom? Thanks for any help.

[Guest Anonymous]

gas tank with clean cloth. (be sure and let sender unit drain fully)

2. carefully remove outer can on sender (nut at bottom) so that the float and wire arrangement is visible, then reconnect sender to wiring harness.

3. Have lovely assistant watch gauge (with ign on) while you slowly move float up and down it's wires. Have her tell you where the gauge reads as you move the float. Those wires the float rides on are resistance wires, and the float has a metal bridge across it that effectively shortens the resistance wires, thus making the gauge read towards full (low resistance) or lengthens the resistance wire so the gauge reads empty (high resistance). Sounds as if the sender itself has a problem, or perhaps you've replaced it with the wrong sender. There is more than one used in 2002s--later cars have bigger (and I think deeper) gas tanks.

All the above presupposes you've made sure the gauge itself is grounding to the car properly by running a ground wire from the back of the gauge to the body. This helps temp gauge problems also.

Good luck

Mike

[Guest Anonymous]

Hmm, I hadn't thought of grounding it. I'll try that. I have in the past done the other thing, but I didn't have help and can't be sure very closely as to what the gauge was reading. Thanks for the ideas.

[Guest Anonymous]

...as Mike said, there are several versions of the sending units. The difference is the length of the sending unit float tube and the travel of the float itself. If you have the wrong unit (it would have to be too short), you would get an empty reading long before the tank is empty.

Chris B.

'73 ex-Malaga.

P.S.: if you don't figure out the problem with the gas gauge, let me know. I will measure the resistance at various float levels on my 02, and you can compare that to readings from your sending unit.

[Guest Anonymous]

might be something silly..

but how do u ground the wires?

on mine, the fuel gauge would show full reading sometimes & on start up sometimes, it shows the correct reading & than jumps back to full...

what else can i do? a bit blur on this stuff...

[Guest Anonymous]

It shoould be the right tube, I believe it's the original. I did buy a few tubes off a guy, but they were the wrong ones- too long, and one was a single wire. I'll try the other things Mike suggested and I'll also test the resistance (when I get a chance, gonna be gone until late sunday) and let you know. Thanks

[Guest Anonymous]

Daryl, your problem sounds like a bad ground at the gauge end. Easy to fix, and works for jumpy temp gauge too. Pull instrument cluster and locate the back side of the two gauges. On each one you'll see a small brass nut. Make a Y shaped wiring harness, slip a terminal under each brass nut, run the wire to a convenient ground behind the instruments on the body (some 02s have one there already, otherwise drill a small hole and install a sheet metal screw. Reinstall instrument cluster and your problem will (probably) disappear.

Also (first) make sure the negative battery cable that grounds to the car's body is good and clean at both ends. If the battery grounds to the engine only, all the body accessories will ground through the accelerator linkage!

Good luck

Mike