70chev Posted July 1, 2011 Share Posted July 1, 2011 So my fuel gauge is in the 3 o clock position. It will come back to working from time to time. I tried cleaning the ground wire that comes out from the top of the tank and it did not help. Is my sending unit shot? Wire broke in the harness somewhere? I see they make new ones, how do I tell if my tank is vented or not? (it is a 70) Give me your thoughts...... Wayne Quote Link to comment Share on other sites More sharing options...
bigtankjones Posted July 1, 2011 Share Posted July 1, 2011 I had an issue with my gage on my '70 a few years back. which turned out to be the plug on the harness for the sending unit that is in the trunk. Check that out. Good luck. Quote Link to comment Share on other sites More sharing options...
7tonemonte Posted July 1, 2011 Share Posted July 1, 2011 to Tony My Cutlass used to lose the gauge off and on, the connection to the wiring harness in the trunk was loose, I was losing taillights too Quote Link to comment Share on other sites More sharing options...
70chev Posted July 1, 2011 Author Share Posted July 1, 2011 I checked the plug and no change. Then I shook the wire that comes through the trunk floor under the car and it came back! Does that wire go through the sending unit, and come out the other side of the tank to mount by the axle? Wayne Quote Link to comment Share on other sites More sharing options...
allchevy Posted July 1, 2011 Share Posted July 1, 2011 If it's brown that wire goes to the sending unit only. The other wire by your axle is ground only.If this brown wire gets broken your gauge will go to the full or beyond. If the wire get grounded it will go to the empty mark. Quote Link to comment Share on other sites More sharing options...
70chev Posted July 1, 2011 Author Share Posted July 1, 2011 the gauge goes way past full. When I shake the wire that goes through the trunk floor (under the car) it will go back to normal. It is the wire that goes to the sending unit. Do I need a new sending unit? Quote Link to comment Share on other sites More sharing options...
MGD72Monte Posted July 1, 2011 Share Posted July 1, 2011 I would say you don't need to replace the entire sending unit because if it was bad, moving the wire would not make any difference. I would inspect the wire for any flaws, drop the tank down if you have to in order to follow it to the sending unit. Quote Link to comment Share on other sites More sharing options...
bigtankjones Posted July 2, 2011 Share Posted July 2, 2011 I would say you don't need to replace the entire sending unit because if it was bad, moving the wire would not make any difference. I would inspect the wire for any flaws, drop the tank down if you have to in order to follow it to the sending unit. Blue Tony Quote Link to comment Share on other sites More sharing options...
NateZ Posted July 12, 2011 Share Posted July 12, 2011 If you haven't narrowed it down yet, here's some troubleshooting to try: 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. Regards, Nate Quote Link to comment Share on other sites More sharing options...
FRANKIE T. Posted July 13, 2011 Share Posted July 13, 2011 Any one have pics of wires connected to the guage? Quote Link to comment Share on other sites More sharing options...
MagicDragon42 Posted July 14, 2011 Share Posted July 14, 2011 Nate, this is a great right-up on trouble shooting a fuel gauge problem. You should submit it to be included in the Technical Archive section. Mike Quote Link to comment Share on other sites More sharing options...
FRANKIE T. Posted February 6, 2012 Share Posted February 6, 2012 any ideas??? Quote Link to comment Share on other sites More sharing options...
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