Pale340 Posted April 3, 2017 Share Posted April 3, 2017 Alright All, I tried a search and read a lot about fuel gauges that go past the full mark regardless of the amount of fuel in the tank, gauges that do not work at all etc., but I did not find anything talking about my problem. My gauge is reading the fuel level but the needle is bouncing. Not much, probably one tick mark back and forth. Also, at night when the headlights are on, when it bounces the lights dim slightly. I thought maybe the sending unit could be bad but I confirmed that the sending unit was replaced a few years ago. Any ideas what this could be if it is not the sending unit? I am not opposed to replacing the sending unit as I really thought this was the problem. However, when I went underneath to look around I saw that the metal tubing coming from the sending unit looked new. I went through the receipts I got with the car and sure enough the sending unit was replaced 1800 miles ago. Any ideas what to check? Thanks in advance for your input. Chuck Quote Link to comment Share on other sites More sharing options...
72-CLASSIC_RIDE Posted April 4, 2017 Share Posted April 4, 2017 Not an expert on this Chuck but I would suspect a bad ground/short based on your explanation. That fluctuation on the gauge needle & simultaneous flickering of lights suggest this. If it's in the fuel gauge itself, or elsewhere, probably going to need a light tester to check for shorts. Would be beneficial if you have a electrical schematic on your car for identifying those locations to check. Has this always been a problem by the way? Maybe caused as a result of replacing Fuel Sensor? Just a thought.............. Good luck and sure others will provide you better advise than mine. Doug Quote Link to comment Share on other sites More sharing options...
Pale340 Posted April 4, 2017 Author Share Posted April 4, 2017 Thanks for the input Doug. It was doing it when I bought the car last year. I did undo the sending unit ground wire from the body and wire brushed it and the body. I reattached it and went and put some gas in it. It did not seem to bounce as bad and I did not notice the headlights flickering. Tomorrow I may undo the ground wire again and clean the body with some sand paper to get a cleaner surface. Hopefully it is just a ground. I would hate to drop the tank, replace the sending unit, put it all back, and end up having the same problem. Quote Link to comment Share on other sites More sharing options...
72-CLASSIC_RIDE Posted April 4, 2017 Share Posted April 4, 2017 I suspected it was a problem when you purchased it. Would be nice to know why the fuel sensor was replaced initially. Maybe it was a problem even before it was replaced. Makes it harder when there are gaps in the history. I hope it's an easy fix for ya.......................... Doug Quote Link to comment Share on other sites More sharing options...
stangeba Posted April 4, 2017 Share Posted April 4, 2017 I copied this from ? someplace, probably here, several years ago. I hope it is correct and helps. Fuel Gauge Problem Diagnosis: 15 Mar 2013 This process can be applied to all recent GM cars except those with computerized gauges. 1) Locate the fuel sender feed wire near the fuel tank. You're looking for a single tan colored wire. With the tan wire disconnected at the fuel tank, the fuel gauge should read past full with the ignition on. Wait a few moments as some fuel gauges take a long time to respond. Touch the tan wire from the body to any convenient ground and the gauge should read empty. If not, you have a wiring problem or a bad gauge. 2) If the gauge responds correctly, the gauge and wiring are OK. Next use a multi-meter to measure resistance to ground of the sender wire connection on the top of the fuel sender or the tan wire from the top of the fuel tank. Measurements should track the fuel in tank. Full - 84-88 ohms Half - 40 ohms, give or take Empty - 0-2 ohms If this doesn't check, then sender or wiring on top of the tank is bad or the sender not adequately grounded. Senders are typically grounded by a black wire which is welded to the sender and attached to the body with a sheet metal screw. 3) If the sender checks OK but gauge and wiring don't, clean the connections, reconnect the sender wiring and separate the Fisher connector (located just outboard of the fuse block under the dash). The gauge should then read past full. Ground the tan wire in the dash side of the Fisher connector and the gauge should read empty. If not, you probably have a bad gauge or possibly a dash wiring problem. Go to Step 5. 4) If the gauge checks OK, then make the same resistance checks to the tan wire in the body side of the Fisher connector. If the readings are different than those at the sender, body wiring has a problem and requires detailed inspection. If they look OK, then the Fisher connector is probably dirty. 5) Clean and reconnect Fisher connector, pull the connector off the back of the gauge and make the same resistance checks to the tan wire. If they don't check, you have a dash wiring problem. If they check OK, your gauge is bad. Gauges can be bench-checked but this is best left to a specialist. Quote Link to comment Share on other sites More sharing options...
Pale340 Posted April 5, 2017 Author Share Posted April 5, 2017 Thanks Bruce. I have done some of that but not all. I will conduct those test to isolate the problem. I am hoping it is a grounding issue. Quote Link to comment Share on other sites More sharing options...
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