gas gauge accuracy, electrical or not?

[wilby34]

ok, so my gas gauge reads three quarters full when it is full. as you might expect it is kinda nerve wracking to look at the gauge and see it on empty and not know how much gas is left.

recently my oil pressure gauge stopped working, it turned out to be a bad connection at the oil pressure sensor in my motor.

Do you guys think that the same thing might be what is causing my gas gauge problem.

if so, where would there be a faulty connection,

and if not, what else could cause this problem?

[carguyinok]

Well, its easy enough for you ta see if it would be the connection @ the sending unit with just 3 wires there. You will find the wires run through the floor in the rear hatch near the pass. side tail

light. There should be three wires you can see from under the car 2 will go to the tank and one ground hooked to the frame rail close by the hole the wires come through the floor.

Now I dont know about A bad con. givin you A false reading I would think if it was A bad con. it just wouldnt read. But stranger things have happend.

[carguyinok]

:beard:

[carguyinok]

green yellow black

[2ManyZs]

If it isn't electrical in nature, the only other thing it could be is that the float has loosened on the shaft and slid. This would be the only other thing that would give a false reading. Clean the electrical contacts, and if it doesn't help, pulling the sending unit might be the only other alternative.

BTW, all the tanks I have seen have had a lot of rust, or the tank was sprayed with undercoating. Either way, it would be a major culprit in the electrical problems if there are any.

[wilby34]

I really appreciate you taking the time to give me those pictures, I will be sure to check those connections out.

[Texaz]

Have you ever pulled the sending unit?

Has your Z always read this way or did it suddenly start?

You may have a bent rod to the float in the tank.

Just another avenue to investigate...:cross-eye

[Nacks]

Hi guys,

I was an Auto Elec. in a former life. There could be another cause for the problem you describe. Most standard instruments tend to run on a lower-than-battery voltage. The problem could be the voltage reg. inside the dash that controls the input voltage to the instrument circuit. 7 volts was the norm. That way, the gauge readings would remain consistent regardless of what the charging system was doing. I could launch into a diatribe of exactly how you can test the fuel gauge wiring but as this is my first Post, I'm not sure exactly how appropriate that information would be. If you're interested, I could probably find out what the resistance SHOULD be through the Sender Unit at full, half-full and empty. That might eliminate the Sender as a possible cause of the problem, plus let you test the gauge.

BTW, my Z does exactly the same thing. I'm not sufficiently motivated to replace the regulator so I just go by how many Kms I've done and reset the trip at each refuel.

[Daniel]

Simple test.Put a jumper wire across the two wires that are attached to your sending unit.With your switch on does the gauge go to full max?If it does then the problem is the sending unit..It's probably got rust/sediment on the float arm and or the area the contact travels on.The sending unit is easily removed by turning the ring at the unit.Of course you want to have low fuel.Shake the unit and listen for fuel in the float.That would limit its travel .There is an adjustment screw on the sending unit should all be well with the unit.Perhaps age has caused increased resistance in the path from sending unit to gauge or the connectors at the tank need cleaning.I rub a little oil on the rubber gasket to aid reinstall and prevent tearing.The fact that your gauge moves and is stable not floating around I believe it is good. Have fun!! Daniel

[Marty Rogan]

I have been reading this post with interest. My gas guage was not too bad until recently, it completely lost its mind.

At first it showed 3/4 when it was full, like someone else mentioned. Then it began oscillating back and forth, at about 1/4 tank increments. It just kept moving as you drove. Later one it just quit all together and showed pegged to empty. It comes back to life once in a while, but I can't trust it at all.

To find the wires coming through the floor, do you have to take the rear, inside plastic finish panel off? To check the sender, do you have to drop the tank?

TIA,

Marty

[Daniel]

Sorry marty,I think your float is caused by the small contact in the gauge becoming old and worn.They look like a set of ignition points.I soldiered across mine and it works fine.Sometimes you can use a burnishing tool which is a very fine emory board and scrub the contacts to give a fresh surface.You will need one of those very small jeweler type screwdriver sets to remove the gauge face.You take the face out and then attach it to a 12v source(Iuse a 120v/12v transformer from a toy) and watch that contact you'll see little arcs between the contacts as it floats.If history repeats itself next will be your oil pressure and temp seem to float in tandem as they share the same contact.I don't know why but you can clean those as I mentioned but,you can't soldier them as they go to max when you switch the key on.Believe me I have spent days and many experiments trying to resolve that puzzle.Even something as simple as a non conduction clip that held the contacts tightly together but NOOOO!!Remove your glove box door,dash liner,then your clock,Then the wires from the amp gauge.Those small ignition wrench set from sears will get that. The test pointsyou ask for from previous text are at the fuel tank under the car behind the right rear tire Tank removal is not needed(I know you're glad about that!).I hope thats where your problem lies. Have fun!!! Daniel

[Marty Rogan]

Thanks Daniel. I have a spare gas guage. Maybe, I'll hook that up to see what happens. If it read fine, then it probably will be the contact problem you describe. That is if that one isn't old and cruddy too!

Looks like a deep dive into the dash is in order.

Thanks,

Marty