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73-87 Chevy _ GMC Trucks => Electrical => Topic started by: Deathscythe on May 22, 2018, 10:49:02 PM
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Hello all, hopefully easy question here. I recently purchased an 86 GMC Sierra Classic with about 240k miles on it. It only has one working tank at the moment (passenger side), when it's full on fuel the needle foes to about the 3 o'clock position. As it runs down the fuel the needle does move.
I guess this will be a two part question; 1.) Will the gauge be accurate as far as empty is concerned or will it show fuel level with it actually being empty? 2.) Is there a simple solution for fixing the over full reading?
I'm pretty mechanically inclined but wiring drives me crazy, so please any answers can be directed as if I know nothing.
Edit: After doing some more extensive searching here.... If the gauge only works from empty to about 1/4 tank, that points to a bad resistor in the gauge. If the tank reads over full when full and about an 1/8th when empty, then that points to a bad ground on the sending unit or tank. Is this correct? I'd hate to have to drop the tank to diagnose this problem.
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Almost correct. Disconnect the fuel gauge wire from the tank sender and ground it with the ignition on. If the fuel gauge indicates Empty, the gauge and its wire are in serviceable condition and there exists excessive resistance in the fuel tank sender or the sender ground. Leaving the fuel gauge wire disconnected will force the needle to sweep past full to ~3:00 o'clock. The sender grounds through a dedicated wire to frame. Often, the frame ground is corroded and can be cleaned with good results.
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I had a sender on one of my tanks do that, ended up being when the float was up (full) it slid past the metal contact portion, thus making the gauge read past full to the 3 o'clock. It also left around a 1/4 tank when reading empty. Bending the float level made it read better.
But start with the basics first.
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Thank you both for the responses. I'll be going through this truck thoroughly to make sure everything is in tip top condition, for peace of mind more than anything. The left tank has a leak, so I'll be pulling and replacing it before too long, since I have it out I'll most likely replace the whole unit to make sure it's working correctly and reliable. Once that's done I'll dig into the right side tank and possibly do the same. Thankfully replacement parts are more plentiful and affordable than they were 10 or 15 years ago.
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Thank you both for the responses. I'll be going through this truck thoroughly to make sure everything is in tip top condition, for peace of mind more than anything. The left tank has a leak, so I'll be pulling and replacing it before too long, since I have it out I'll most likely replace the whole unit to make sure it's working correctly and reliable. Once that's done I'll dig into the right side tank and possibly do the same. Thankfully replacement parts are more plentiful and affordable than they were 10 or 15 years ago.
Good topic,
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