71 Chevelle sweepdash fuel gauge reads full (Troubleshooted) - Chevelle Tech
Electrical & Wiring Troubleshooting electrical problems.

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post #1 of 6 (permalink) Old Aug 7th, 19, 6:15 PM Thread Starter
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Murph
 
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71 Chevelle sweepdash fuel gauge reads full (Troubleshooted)

My 71 Chevelle (Sweep dash) has a new tank and sending unit. The gauge on the dash reads passed full. I've read probably 15-20 posts and websites about fuel gauge troubleshooting and honestly I think I'm overwhelmed/confused from the various things I've read.


I have not dropped the tank yet and dealt with the sender directly.



Here is breakdown of the testing:

  1. Unplugged connector/rubber boot at license plate: Grounded tan wire -- Gas gauge goes to Empty
  2. Grounded tan wire at harmonica connector -- Gas gauge goes to Empty
  3. Grounded tan wire at gauge -- Gas gauge goes to Empty
  4. I also checked the ohms coming through the tan wire at all 3 locations and at all 3 it read 50-52ohms. (Trunk, Harmonica, Gauge)
  5. Replaced the ground at the gauge with a good known ground. When unplugged it went to empty, when the ground was plugged in it goes back to full.
  6. Replaced the ground from the sending unit to the frame under the car with a good known ground. No change in fuel gauge.


So here is where I get confused. I then bought an aftermarket fuel gauge and hooked it up inside the trunk. I ran jumpers from the Tan sender wire, power, and a good ground. With no ground plugged in, the aftermarket gauge reads past FULL. With the ground, it reads empty. Ohms check showed 50-52.



I've read that a full reading means a bad ground or an open TAN wire. I figured if I wired up an aftermarket gauge and it worked in the trunk I could then move forward to the harmonica connector, and if it worked there, passed that to the dash.




I think the sending unit is faulty or grounding itself out somewhere, which will require me to drop the tank. Any help would be appreciated! Thanks.

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post #2 of 6 (permalink) Old Aug 7th, 19, 6:31 PM
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Re: 71 Chevelle sweepdash fuel gauge reads full (Troubleshooted)

This is confusing. The connected ground should operate the gauge. Very unlikely, but is the sending unit installed backwards inside the tank?

It's a pretty common problem on these cars that the sending unit is usually the culprit when the gauge is pegged on Full.

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post #3 of 6 (permalink) Old Aug 8th, 19, 7:01 AM
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Re: 71 Chevelle sweepdash fuel gauge reads full (Troubleshooted)

Did you put the new tank and sender in. Could you have pinched the tan wire between the tank and the trunk floor. If you drop the tank out pull the sender and keep it hooked up. Move the float level rod to see how the gauge reads. You can move it in quarters, empty, 1/4, 1/2, 3/4, and full. See how the different positions correspond with the gauge.
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post #4 of 6 (permalink) Old Aug 11th, 19, 1:20 PM Thread Starter
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Just a little update: been driving a good amount letting the fuel run down. The gauges needle has begun to bounce around while driving. When I'm parked, as of right now the gauge reads 1/4 tank. I checked the ohms and I'm reading ~30amps.


Waiting to run the gas down before I drop the tank. But I suspect/agree that it is the sending unit. Maybe it's pinched? I did not put it in

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post #5 of 6 (permalink) Old Aug 13th, 19, 1:14 PM Thread Starter
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Managed to drop the tank and test the sending unit. Here's where it's at:

Sending unit ohms arent steady/consistent. Jumps around wildly.

Hooked old gauge up to new sending unit, didn't read properly.

Hooked old sending unit up to new gauge, didn't read properly.

Hooked new sending unit up to new gauge, read properly.


So at this point I think both the gauge and sending unit are both junk. I can't find any sweep dash fuel gauges (ha ha) to replace it so I'm gonna run an aftermarket gauge under my dash. I would like to replace my dash with an SS dash in the future anyway. Thanks for all the help!

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post #6 of 6 (permalink) Old Aug 13th, 19, 7:40 PM
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Re: 71 Chevelle sweepdash fuel gauge reads full (Troubleshooted)

Quote:
Originally Posted by Cancel View Post
Managed to drop the tank and test the sending unit. Here's where it's at:

Sending unit ohms arent steady/consistent. Jumps around wildly.

Hooked old gauge up to new sending unit, didn't read properly.

Hooked old sending unit up to new gauge, didn't read properly.

Hooked new sending unit up to new gauge, read properly.


So at this point I think both the gauge and sending unit are both junk. I can't find any sweep dash fuel gauges (ha ha) to replace it so I'm gonna run an aftermarket gauge under my dash. I would like to replace my dash with an SS dash in the future anyway. Thanks for all the help!
Ask around, I bet some one here has a sweep dash gauge.

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