Fixed my fuel sending unit
#1
Thread Starter
Senior Member
Joined: Apr 2006
Posts: 510
Likes: 0
From: Murphy, TX
Car: 1990 formula
Engine: 433 sbf + turbos
Transmission: powerglide
Axle/Gears: fab9, 3.50
Fixed my fuel sending unit
Like many of you, I experienced a gas level gauge that was constantly stuck on full. I happened to be dropping the tank to sump it, so I decided to investigate to see what was going on.
Unplugging the fuel pump and sending unit showed a full level on the gauge. Shorting the black to tan wire locations on the body side connector showed a level of empty so deduced that the wiring and gauge were good.
I then used a multimeter to ohm out the purple wire on the sending unit itself while moving the float up and down.... The multimeter read open circuit.
I priced some new sending units and they seemed to start at $188 which gave me some more motivation to try to figure out the problem.
I saw that the sending unit was held together by 3 tabs which were folded over, two on one side and one on the other. I pried back the one tab by itself and pulled the sending unit case apart.
Inside was a metal strip with many folded up contacts. The shaft that the floater was connected to had a spring loaded contact which touched the metal strip at different points depending on the level of fuel in the tank and the position of the floater.
What i discovered was twofold: first and most importantly, the metal strip had a tab connecting it to the sending unit case and on my unit, it was making insufficient contact to the strip, so i bent it down. After that, i put the unit back together only to find that the unit read full scale resistance no matter what the position of the floater.
I took the unit back apart, used a bit of sandpaper to clean the contact on the shaft, then bent the contractor a bit more to preload it against the strip, put it back together, and it worked!
Unplugging the fuel pump and sending unit showed a full level on the gauge. Shorting the black to tan wire locations on the body side connector showed a level of empty so deduced that the wiring and gauge were good.
I then used a multimeter to ohm out the purple wire on the sending unit itself while moving the float up and down.... The multimeter read open circuit.
I priced some new sending units and they seemed to start at $188 which gave me some more motivation to try to figure out the problem.
I saw that the sending unit was held together by 3 tabs which were folded over, two on one side and one on the other. I pried back the one tab by itself and pulled the sending unit case apart.
Inside was a metal strip with many folded up contacts. The shaft that the floater was connected to had a spring loaded contact which touched the metal strip at different points depending on the level of fuel in the tank and the position of the floater.
What i discovered was twofold: first and most importantly, the metal strip had a tab connecting it to the sending unit case and on my unit, it was making insufficient contact to the strip, so i bent it down. After that, i put the unit back together only to find that the unit read full scale resistance no matter what the position of the floater.
I took the unit back apart, used a bit of sandpaper to clean the contact on the shaft, then bent the contractor a bit more to preload it against the strip, put it back together, and it worked!
#3
Thread Starter
Senior Member
Joined: Apr 2006
Posts: 510
Likes: 0
From: Murphy, TX
Car: 1990 formula
Engine: 433 sbf + turbos
Transmission: powerglide
Axle/Gears: fab9, 3.50
Re: Fixed my fuel sending unit
Got the tank back in, put 5 gallons in the tank and the level on the gauge appears to be correct.
#5
Member
Joined: Mar 2012
Posts: 195
Likes: 0
From: Omaha, NE
Car: 1987 IROC-Z
Engine: Vortec 350 crate #12530282
Transmission: 700-r4 Auto
Axle/Gears: 3.23
Re: Fixed my fuel sending unit
Is this fix still holding up? I'd much rather not buy a new sending unit, and my gauge reads just under half full with I fill it up completely…..
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Ghettobird52
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07-05-2024 11:18 PM