The Stovebolt Site Forums The Shop Area The Electrical Bay Gas gauge needle off the chart

My 58 cameo all original sending unit and gas gauge has always read off the right side(full) when full tank is full and 1/2 tank when empty . Do inhale a sending unit problem or a gas gauge problem ? Can the needle be taken off gauge and repositioned to solve this problem? The gauge does move down as tank empties but only to the half tank point ,,,that's when tank is empty. Thanks for suggestions.

First is to add a ground wire from sender mounting screw to frame clean spot. You can just run temporary test wires all the way from sender flange screw to battery ground post. Run it along outside truck if you want. Then same for gauge body. 80% of issues with gas gauge problems is ground.
Do the testing as described on internet for testing sender/gauge.
Gauges can be tweaked both electrically and mechanically (needle) if that's all that is wrong.
"Always read wrong" ??? sender/gauge old or new? Never inspected? Never removed by you? Sure not wrong aftermarket parts/wired wrong by previous owner?

From The Net

TESTING If your gauge reads FULL AT ALL TIMES:

A. Probable Causes
1. Wire from dash gauge to sending unit is broken and/or the connection is corroded (not making a good electrical connection).
2. Resistance wire inside sending unit is broken
3. Sending unit is not properly grounded to tank or tank is not properly grounded to chassis

B. Testing
1. Remove the wire from the contact stud on the sending unit and ground it to the chassis. If the gauge now reads Empty, the trouble is either poor grounding of the sender or a bad sending unit.
2. If the gauge still reads Full, touch a grounded test wire to the sending unit terminal on the back of the dash gauge. This terminal is often marked with a red tag. If the gauge now reads Empty, the wire from the dash to the sending unit is broken or the connection to the dash gauge is corroded.
3. With the sender removed from the tank, connect an ohm meter to the sending unit (one lead to the contact stud and one to the housing) and check the resistance of the sender as you manually raise and lower the arm. This reading should be 0 to 30 ohms (or very close).
4. If none of these tests finds the problem, the dash gauge is the problem and should be rebuilt or replaced.

C. Repairs
1. Make sure that a good ground is present at the dash gauge and also at the sending unit. Run a separate ground wire to the chassis if necessary.
2. Sliding contact arm may not make good contact to the resistance wire windings in sender. If you are experienced with electrical repairs you may be able to clean the wiper and resistance wire coil or replace the wire. Otherwise send the unit to a specialist or replace the unit.
3. Check for good ground at sender body and gas tank.

Ground was my issue.

Thanks guys.

Thanks for all the detailed checks and test. So nice to have someone include all the steps for good advise, Pete

It reads past the full point all the way off gauge to right side of full, when full. It goes down as gas is used to the halve tank mark when tank is empty. Seems the needle is not in proper position on gauge

You may be able to bend your float arm to correct your over-full/half tank issue.

Sounds like a possible impedance mismatch issue to me.

Good suggestion, TIny

txpete,

You have had this problem since you got the truck - you have not had the truck all its life?

Someone could have used a newer sender (1965 or newer for GM, which had different impedance 0-90 ohm vs earlier 0-30 ohm).

Thanks for all the great problem solving answeres

Let us know what the problem was so we can save it in our memory bank for ourselves and others. That's all we ask.

Thank you sir but my gauge does not read full all the rime, it reads way past ful ( of the gauge) when full and half tank when empty. Any ideas? Could the needle be on gauge wrong?

can't 'adjust' the gauge needle, more likely what Carl indicated, need to bend the float arm to read correct - when you pull the float out check it by hand operation to insure it's got the full range of movement and reads correctly, might just be a bad'un

Bill

Did you read my post about impedance? Are you running a 30 ohm sender and a 30 gauge?