How do I test fuel gauge sending unit?
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Joined: Mar 2000
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From: Hampstead North Carolina
How do I test fuel gauge sending unit?
I took my sending unit and fuel pump out this afternoon to determine why my fuel gauge stays near full even after the car has been driven several miles. Does anyone know how to test the sending unit with a voltimeter? I did a search on the subject, but no one was explicit in where to attach the leads. Any help would be greatly appreciated.
Instructor
Joined: Nov 2002
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From: ELLICOTT CITY MD
Re: How do I test fuel gauge sending unit? (Skydiver)
if i remember correctly there is only three wires going to the tank sending unit. one is the power for the pump(which should be very easy to determine which it is with the unit out), one is the ground for the hole unit and pump, and the third is the sending unit. you should be able to hook the black wire of a volt meter to the housing of the unit and the other to the sending unit wire that runs to the float and set the meter on ohms and read the resistance. the resistance should go up and down with the float level smoothly. any jumps or spikes will show a bad sender. of course you could always just plug it in and try it with the car guage. if you do it that way then you will have to cycle the key to eliminate the slow responce of the anti-slosh module. hope that helps! :chevy
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Joined: Mar 2000
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From: Hampstead North Carolina
Re: How do I test fuel gauge sending unit? (Skydiver)
Thanks for the quick reply. What would you consider a large jump or spike. It moves up a couple of ohm's at a time, but no large jumps.
Thanks.
Thanks.
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Joined: Mar 2000
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From: Hampstead North Carolina
Re: How do I test fuel gauge sending unit? (Skydiver)
After testing the unit, I have a hard time beleiving the unit is faulty. At empty it reads 0 ohm's and around 100 at full. It rises and drops somthly as you raise or lower the arm. Does anyone have a suggestion as to what to check next if its not the sending unit? Thanks.
Melting Slicks
Joined: Apr 2001
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From: Ca.
Re: How do I test fuel gauge sending unit? (Skydiver)
Try plugging the harness back together while it's out of the car; Then check the dash gauge-if it shows half full at half ohms etc. then they're both good. Keep in mind that there is a good delay between movement of the fuel sender and the dash readout changing-it's dampened intentionally. You can turn the key on and off to speed up the updated readout. On mine dash and sender were good-I just "manually adjusted" the sender to "calibrate" it. :yesnod:
Burning Brakes
Joined: Nov 2002
Posts: 807
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From: Los Altos CA
Re: How do I test fuel gauge sending unit? (Skydiver)
I don't think there is anything really wrong here. The system as designed by GM is just not very accurate. I had the same problem with mine and have read of other people with the same problem on this forum. Mine used a third of the fuel before it started to show any drop at all. I fixed mine by installing a resistor between the tank sensing wire and ground. Since you have the sender out, you can probably find the required resistor by making some measurement. Find the resistance where the gage just starts to drop. Call that R1. Then measure the resistance when the float is full up. Call that R2. Call the parallel resistor you need R3. Then find the parallel resistance required to make the gage read correctly from 1/R1= 1/R2 +1/R3. For example, if R1=90 and R2 =100, then R3 = 900. I think I needed a resistor close to 500 ohms for my car. This resistor will have very little effect when the tank is close to empty. If you bend the float arm, you will have less accuracy when the tank is close to empty.
