Originally Posted by Dano222
, My 92 fuel gauge isn't working either just kinda excepted it as it do to the $$$ of a new sending unit. Gage is always reading full, would a bad ground cause that? I have cleaned the circuit board contacts and connector in the gauge pod few weeks back, didn't help. Didn't know about the ground, is it located in the area of the tank sending unit? Thanks . . . there still maybe some hope.
So this is a FAQ that I have been making by collecting data from forum posts. I have not factually checked any of this info. I haven't dropped the fuel tank nor have I repaired my faulty gauges. Just collecting info so when I am ready I have it.
That being said take the following with a grain of salt, it may not be correct. (if any one sees incorrect information please call it to my attention)
The sending unit is basically a variable resister that increases resistance as the float goes up. No resistance to ground will show an empty tank where as a higher resistance will show something between empty and full. I have read that full is around 88 ohms. I have also read that the resistance for full is different between the different engines, also that there is different gauges for the various engines. Not sure if that is true or not
A pegged gauge could be several different issues. Bad gauge, bad sender, bad wiring, corroded connectors or a stuck float.
If you have issues with other gauges as well its very likely that it’s the connector/circuit board behind the gauge assembly. These are known to be problematic. Pull the gauge cluster and clean the contacts on the connector and circuit board with an eraser or emery cloth. A squirt of dielectric grease when you put it back together will help this from becoming an issue again.
If the gauge returns to E when the key is off, it is likely that the gauge is good. If it stays pegged at all times, it is possibly bad.
There is a cup that the float sits in which deforms after years of sitting in fuel. If this happens the float can hang up on the cup. This is usually the cause of a gauge hanging up at ˝ full and never going to empty. If this is the issue, drop the tank and rip the cup out and throw it away. The other option is to bend the float rod. Here is a link:
Assuming the gauge is good; I would then suspect the wiring. The easiest way to check the wiring is to disconnect the gauge. Then meter for resistance from the sending wire to ground. With a full tank it should read 88 ohms to ground, 1/2 tank is 44 ohms to ground, empty it should read a short or zero ohms to ground. If these numbers check out then the gauge is bad. You can also short the gauge to ground and this will send your gauge to empty if the gauge functions correctly.
If the ground from the sending unit to frame is not making connection, that will send the gauge to full. If the wire from sending unit to gauge is shorted to ground (pinched between metal, insulation abraded off, etc.) that will send the gauge to empty. If the sending wire is cut but not touching metal the gauge will read full.