It's not a big deal, but my fuel gauge is flipping out. The gauge always worked fine until I dropped the tank back in March to access the rear leaf spring bushing pins. When I put everything back together, the fuel level gauge was way off, so I pulled the sending unit out and inspected it. It seemed fine, but I guess when I dropped the tank the float got out of whack. I re-calibrated the sending unit to match the gauge to the proper level and everything seemed fine after that. A few weeks later the needle would bounce around on occasion. I replaced the ring terminal and clean the connection at the sending unit and double checked the connections at the gauge. It's just an aftermarket GM type sending unit, and a cheap gauge from the parts store. The gauge works as it should about 60% of the time, the other 40% of the time, it's twitching around from "E" to "F", and sometimes flickers around between "E" and the actual fuel level in the tank. You can hear the gauge clicking slightly when it moves. I took a video, but having troubles uploading it to YouTube from my phone. Is there a way to test if the issue is in the sending unit, or in the gauge?
It's been a while since I troubleshot one of the older units, so I hope I can explain this correctly: They work on resistance. A lot of resistance when the float is dropped reads empty. A little resistance when the float is up reads full. Pull the gauge wire from the tank unit, open circuit = lots of resistance, gauge should go to empty. Ground it = little resistance, and the gauge should climb towards full, assuming gauge is ok. If your gauge bounces to empty when the tank's empty, it could be an intermittant open circuit. After checking the sending unit ground, I would then look for an intermittant open (corroded crimp?) somewhere between the tank and gauge. Sending unit often grounds to the tank, if so, is your tank grounded well? After eliminating wiring, then I would suspect either sender or gauge. Got to pull the sender, but an ohmeter would be the tool to measure resistance as you move the float thru its range of motion. Obviously, hardest problem to nail is an intermittant one. Hope this helps.
I don't specifically know Chevy's, but alot of sending units have a capacitor either at the tank or at the gauge. The capacitor "buffers" out the swings of the float unit.
The mentioned information is mostly correct, depending on the model of gauge/sender the resistance direction/relation. I.E.: high resistance= full, low resistance = empty or vice versa. The relationship is not universal. If you have an aftermarket GM sender it is likely 0-90 ohms empty -full. Use an analog ohm meter to check the sending unit in order to visualize any intermittent points along the travel of the float. Double check all you ground connections and the sender wire to the gauge. Aside from that, to mess with the internals of an aftermarket gauge is a waste of time. Just buy a new one made in the same ohm range.
the bad grounds deal don't make any sense to me....If the tank were every now and then either grounding itself and then not why would that make the needle peg full? The ground still has to go through the sending unit. Do these type gauges have a "vibrator" or some type of voltage regulator built into them to "average" the gauge readings
IF the sender grounds to the tank (sometimes at a mount screw for the sender), then the tank must also have a good ground for the circuit to complete. If the tank looses ground, then resistance goes way up, causing the gauge to react. MORRISGAUGE is correct, sometimes the low resistance/full gauge reading is reversed. God, I hate getting old.
If you momentaraly ground the sender wire, it won't peg full to the point where the needle clicks the face of the gauge......it will GRADUALLY swing to full. That is why I don't think the ground is the problem. Easy enough to check, but not the problem. I still think the problem is the + side. Or the gauge, if it regulates voltage.
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