Batmobile66

I'll keep it simple. My gas gauge is WAY off! The needle rests around the full mark when the key is off. When you turn the key on the needle moves up and out of view. I dont know if a can just reposition the needle or how intensive it is to get to the gauge. What do you guys think?

jeffreyalman

from the limited knowledge I have, I am guessing the problem is in the tank at the sender. It may be in an electrical connection going to the sender, or at the gauge itself. My Toronado required a sending unit, my Custom Cruiser required a slap on the dash (do not use a fist)

jaunty75

Yes, it sounds like the pointer needs to be repositioned, but the first question is, does the gauge actually work? Also, how low does it go when it's time to fill the tank? Does it drop down to near "E", or did you try that once only to have it run out of gas? Where the needle rests when the key is off doesn't really tell you anything.

IF the sending unit and gauge are working properly, the gauge should read Empty if the wire from the sending unit to the gauge is disconnected at the sending unit end (or at a connection point along the way) and grounded. When you disconnect it but before grounding it, it should read Full or above. The sending unit is just a variable resistor with the resistance varying between 0 and 90 ohms. When you ground it, you've got 0 ohms, and that's the "E" condition. With an open circuit, the resistance is infinite (in other words, a lot larger than 90 ohms), so the gauge not only reads "F," but above it.

If the gauge doesn't do these things when the circuit is grounded and open, then the gauge is bad. If it does, then it points to something wrong with the sending unit. Getting at that means removing the gas tank.

Batmobile66

When the gauge is at the "rest" position the needle is just above the F. When i turn the key on or start the car the needle moves upwards. The gauge acts as if its working right, just the needle is off. If the fuel float was bad or short to ground then why would the gauge move when the key is on? Maybe high resistance in the circuit?

jaunty75

The gauge wouldn't move if the circuit were shorted at any point regardless of the amount of fuel in the tank. Turning the key on causes the gauge to move to wherever the resistance in the circuit tells it to, even if it's shorted. Does the gauge move at all as the amount of fuel in the tank changes?

Your idea that there might be high resistance in the circuit is a good one. If true, it suggests that the wiring might be corroded at a connection point, which is all the more reason to give the wiring a good looking over all the way from the gauge back to where it connects to the sending unit on the top of the tank. Also check the ground wire that comes off the top of the tank and attaches to the body under the car in front of the tank. If that connection is corroded or loose, you would also have high resistance.