#1  
Old 08-01-2020, 12:59 PM
Doctor john Doctor john is offline
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Default Fuel Gauge Malfunction

I'm having problems with my fuel gauge. I think I have about 1/2 tank but gauge reads empty with key on. Per shop manual diagnostics, disconnecting sender feed wire, gauge goes to full, but very slowly. When I ground feed wire, gauge goes quicker to empty, so I thought it was bad sender. I connected a new sender unit and gauge stays on empty no matter how I move float arm. I have continuity from gauge to sender wire at sender and sender is connected to a good ground, no difference if I use different ground locations. Of course this is all done with key on. I tested resistance of new sender and it varies from 4 to 97 ohms depending on position of float arm, so sender seems fine. Any ideas?

  #2  
Old 08-01-2020, 01:28 PM
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Peter Serio Peter Serio is offline
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Default Fuel gauge: troubleshooting

I would think the problem is either a bad fuel gauge (I rebuild and repair those). That or you have a corroded and or loose plug-in connection in the body wiring. Check the 2 tabs at the rear of the gauge for rust or corrosion, next inspect the dash wiring right where the dash harness connects to the flat-wire harness (it's the black one that runs underneath the carpet). Also from inside the trunk right behind the rear seat that flat wire harness re-connects back to a round wire harness.


Loose or dirty copper tabs inside of those plastic plug-ins can lead to a fuel gauge not working. That or a pinched or damage wire somewhere along the run from front to rear. If you suspect it is the gauge; if you remove that & send it to me I can test that for you.

You can remove it from behind, there are 2 screws that hold it on. The gauge has a small silver plated access panel built into it. That panel is the ground for the gauge. All GM fuel gauges need a ground at the dash as well as one more which is located underneath the trunk floor.

Photo #1 the plug-in for the back of the fuel gauge has 2 wires in it. The dark brown wire should test as 12 volts battery + with the key on, & zero volts = key off. The tan wire is the wire that runs all the way back to the tank sender. The sender then has a black wire spot welded to the edge of the retaining ring edge. That wire attaches to body ground. (Underneath the truck floor). This ground is sometimes in a rusted area and you may re-locate that ground as needed.
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  #3  
Old 08-01-2020, 02:11 PM
Doctor john Doctor john is offline
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Thanks Pete. The ground at the tank is good as I've cleaned the connection to bare metal. I have continuity from the tan wire behind the gauge to the terminal for the sending unit; does that rule out a pinched wire? How do I send you the gauge and what does it cost to test/repair? Thanks

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Old 08-01-2020, 07:42 PM
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Peter Serio Peter Serio is offline
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When you say you have continuity in as far as the tan wire goes can you describe what test did you do to verify that? A pinched tan wire would conduct voltage to ground. That wire only has about 3 or 3 & 1/2 volts in it with the key on. The tan wire is, by design intended to be grounded (at the sender) as would be the case when your fuel level is very close to E. So a pinched and grounded tan wire does not pop a fuse. But it will cause your fuel gauge to read E all the time. Even if there is more gas in the tank.

If you are sure that the wiring is ok then it is probably the gauge. Those gauges will go bad after 50+ years of use. I can't say what it needs until I can see and inspect it here. I have had very good success at fixing old GM car gauges. A typical repair to a fuel gauge runs right around $100 up to $110 parts and labor. You can PM me for the shipping info.


One thing is when you remove the gauge from out back of the dash, leave the silver colored access hatch or rear panel intact. The pointer is made from soft, very thin aluminum. There are NO new pointers available as service or repair parts from GM for any of these 1960s or 1970s car gauges. You want to create an "air space" of protection above the dial where the pointer is. You can do this using a piece of corrugated cardboard or a small plastic food leftover container with a lid. Just made sure if you send a gauge to me in the mail; that nothing inside of the box as far as packing, can touch or press up against the pointer. The pointers are easily bent or broken when not in the dash as they are open in mid-air. The lens over the top of the gauges in your car gives the pointer an air space to move in, and fully protected. Just FYI; during all normal operation of any GM car gauge the pointer(s) should never come into contact with any other object.

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Last edited by Peter Serio; 08-01-2020 at 07:49 PM.
  #5  
Old 08-01-2020, 09:49 PM
Doctor john Doctor john is offline
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I used a multimeter on continuity mode connected to end of the tan wire disconnected from the gauge and to the other end disconnected from the sender unit and had continuity. The rear harness and ribbon harness to rear were replaced last year. I am planning on replacing dash harness this winter.

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Old 08-01-2020, 10:18 PM
Jonsie Jonsie is offline
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Peter-not looking to hi-jack this thread, but can you tell me what year/model that fuel gauge is from? Thx

  #7  
Old 08-02-2020, 01:56 AM
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Peter Serio Peter Serio is offline
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Hi, the Fuel gauge in the photo will fit & work in a '65, 66 or 67 Tempest, Lemans or GTO with standard dash.

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  #8  
Old 08-26-2020, 08:30 AM
Doctor john Doctor john is offline
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SOLVED! I discussed with Pete Serio, sent him the gauge. It had a few issues he corrected quickly and inexpensively but nothing to explain the situation. When I reinstalled gauge it went to below empty. For the hell of it I tried jumping a ground wire from gauge body to a good ground and the gauge worked. It appears my dash grounding strap is defective. I need to redo the dash wiring harness--another project this winter.

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