Fuel sending unit
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Senior User
Joined: Oct 2006
Posts: 278
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From: MINNESOTA
Fuel sending unit
My fuel gauge went to full all the time. Because of plastic tank checked where I figured ground was connected to post under dash by radio and it checked out ok. Tryed to feel on top of tank for wires and seem to be hooked up. Tank is 38 gallon mounted mid-ship. Is there anything else to check before dropping tank for new sending unit? Gauge acted funny not reading right a fill or so before it when to staying on full. It does start to come off full about a 1/8 when you get 250 miles on and it takes 20 gallons to fill.
Senior User
Joined: Oct 2004
Posts: 160
Likes: 0
From: King George, Virginia
You can test the variable resister in the take without removing the tank. You will find a plug on top of the tank where the sending unit sends the signal to the computer. Take a meter and set to resistance. Where to two wires enter the plug (tank side) insert a couple of stiff wires like a paper clip. Attach a couple of wires to these and run this up into the cab. Hook your meter up in the cab and before you start the truck take a resistance reading. Once you turn on the ignition, 2 to 3 volts are applied. Take these reading for a tank of fuel.
Full tank will read 165 ohms
Empty tank will read 15 ohms
Fill the tank and as the miles add up, the resistance should fall off from 165 ohms down to 15 ohms if you run it almost out. After a few hundred miles, I'm sure you will know if this resister is working.
The little variable resister in the tank can be cleaned, it's just delicate.
This test will at least isolate the possible cause.
Full tank will read 165 ohms
Empty tank will read 15 ohms
Fill the tank and as the miles add up, the resistance should fall off from 165 ohms down to 15 ohms if you run it almost out. After a few hundred miles, I'm sure you will know if this resister is working.
The little variable resister in the tank can be cleaned, it's just delicate.
This test will at least isolate the possible cause.
