Fuel sending unit voltage?

[this man]

Hey, Does anybody know how many volts you're supposed to have at the fuel sending unit wire where it connects to the fsu, and how many you're supposed to have at the fuse box?

Thanks in advance

[Tim Christian]

You don't have volts but you do have 90 OHMS

[elf w/capital T]

Disconnect the sending unit wire. Ground it out and the gauge should move to 3 o clock postion (with the key on!!)

The resistance on the sending unit should read 0-90 ohms from the post to ground. (depends on how much GAS you have in the tank)

Just replaced mine and works fine now.

make sure the wire coming from the sender to the fuse box doesn't have any breaks or anything shorting it out...


http://www.chevytrucks.org/tech/gasgauge.htm


http://www.6066gmcguy.org/Electrical-02.htm

[69heavychevy]

it doesnt have any voltage, its a ground more or less...whatever you do dont apply any voltage to it unless your considering burning your truck down...

[pumpkin]

Power goes to the fuel gauge, and out through the sending unit wire. There is power there, but I have never measured it. The circuit is then completed by a varible resistor (sending unit) to ground.

[panhandler62]

If you read from the disconnected wire at the sending unit to ground you should have ~12v. If you read from the connected wire to ground you are going to get results that are hard to interpret because you now have 2 ground paths.

It's likely that the instrument will provide almost no impedance and you'll see ~12v (and your gauge will peg) but if the tank is full (or the sender is shorted through) you'll have 2 nearly identical paths to ground and you'll split the current and get an unexpected voltage drop.

As mentioned above; the fuel gauge measures the voltage drop on the circuit which is a function of current restriction. The variable resistance of the sending unit alters the voltage drop by restricting current as the tank fills. The sending unit doesn't actualy send anything. Think of the fuel gauge as a flow meter on a pipe; the more flow the higher the reading. Turn the valve (the sending unit) towards closed and there is less flow and the gauge reads lower.