How to test fuel sender?

[DiscoJen]

It's a 24 volt unit. I've freed it up already cause it was stuck as stuck could be, but still doesn't register. It appears to be intact and in good shape. It could just be a wiring problem, but I want to learn how to test the unit so I can do all the steps of tracing my issue while I've got it all apart.

Guess it'd be a good idea to test the fuel gauge, too. Any tips on how to do that as well?

I'm terrible at electrical work so it's ok if ya explain it like I'm a 4 year old. :bigok:

Thanks all!
Jen

 

[ajtbussen]

You can use an Ohm meter and measure the resistance of the sender and see if it changes when you move it. Call me and I'll come and show you.

AJ

 

[Ron]

Hook up to ohm meter, move rod, ohm meter should move somewhat linearly.

 

[apg]

I don't know about 24v systems, but 12v vehicles had a voltage stabilizer for the fuel and (electric) oil pressure and water temperature gauges. As others have said, the gauge in each case functions as an ohm meter, registering how much 'lectricity leaks back to ground though the sender. This voltage stabilizer - which reduces the voltage to about 10.3v - can and does go bad with age.

Consider the voltage path in your trouble-shooting. Current goes first to the instrument voltage stabilizer, then to the gauge, then to the 'sender' then back to earth. The fuel sender can be carefully pried apart to reveal very fine nichrome or resistive wire wrapped around an insulator. A 'wiper' attached to the float arm makes the contact and may be buggered with corrosion.

Try to ignore the fact that there's an electrified, sliding contact inside your fuel tank....

Cheers

 

[stevenmd]

I don't know about 24v systems, but 12v vehicles had a voltage stabilizer for the fuel and (electric) oil pressure and water temperature gauges. As others have said, the gauge in each case functions as an ohm meter, registering how much 'lectricity leaks back to ground though the sender. This voltage stabilizer - which reduces the voltage to about 10.3v - can and does go bad with age.

Consider the voltage path in your trouble-shooting. Current goes first to the instrument voltage stabilizer, then to the gauge, then to the 'sender' then back to earth. The fuel sender can be carefully pried apart to reveal very fine nichrome or resistive wire wrapped around an insulator. A 'wiper' attached to the float arm makes the contact and may be buggered with corrosion.

Try to ignore the fact that there's an electrified, sliding contact inside your fuel tank....

Cheers

Can you restate that in "idiot terms" for me?:kyle: What do I look for? What the hell is an ohm meter? Can I buy that at Crap Zone? And what do I do with it?

 

[DiscoJen]

Try to ignore the fact that there's an electrified, sliding contact inside your fuel tank....

Nothing like sitting on two fuel tanks with a pair of batteries sitting between them! I'm a human wick. :ack:

Thanks all for the very detailed information. Tomorrow looks like nice weather so I'll break out the multimeter and pretend like I know what I'm doing with it. If that don't work, AAAAAAAA JJJJJJJJJJJJJJ, keep yer phone charged!

After running out of gas for the 4th time this past weekend I'm determined to get to the bottom of this.

 

[apg]

Can you restate that in "idiot terms" for me? What do I look for? What the hell is an ohm meter? Can I buy that at Crap Zone? And what do I do with it?

An Ohm meter measures resistance in a circuit - which is what the 'senders' do - vary the resistance. Rat Shack sells a nice pocket-sized multi-meter for about $20. The newer ones even have a self timer to turn itself off, as I did so many times with the older one. (Got tired of buying those damn expensive little batteries....)

To see if the fuel sender is working, remove it from the vehicle. The red wire will go to the single spade fitting on the top of the sender (though I have seen some that have a ground connection, too.) The black lead gets fixed to the body of the sender. Moving the arm should change the resistance - measured in ohms - on the gauge. 30 to 300 or so, IIRC....

Of course, the reverse is true if you have a "positive earth" vehicle....

Now, for extra credit, write a 100 word paragraph on "Ohm's Law"....

Cheers

 

[DiscoJen]

Results:

The fuel sender works. Put it back in, no worky. Cleaned the connections and traced the wire and it seemed to be intact. White wire from the drivers tank, black wire from the passenger tank. Traced them to the fuel switch valve thingy and one wire was plugged into one side of it, and the other wire into the other side.

Took the passenger side wire off and plugged the drivers side wire in it's place thinking that maybe it was connected to the wrong side. Sure enough the gauge read 3/4 of a tank! Then when I plugged the passenger wire back in to the other side and the gauge dropped to empty again. Left the passenger wire off and now the drivers side tank reads the 3/4 again which is just about right. Yes, I have the valve switched to pull from the driver's side.

There is a green wire on the fuel switch valve thingy that connects both sides of the valve. I wonder if that is supposed to be there like that.

 

[Ron]

Jen, I wish I could help, but I am not familiar with the wiring for dual tanks.

 

[DiscoJen]

No problem Ron, we can't win them all and you've always been a huge help.

I think by leaving the passenger tank sending unit disconnected that I'm getting a good reading. It read 3/4 tank the other day, after driving around town running errands it now says 1/2 tank. I can live with that and am pleased that I learned enough about ohms/multimeters to get that far.

Does that fiberglass tailgate you have fit a Series BTW?

 

[Ron]

No, it does not, it is slightly the wrong shape and the hinges are interfered with by the drip rail. BTW I am looking for a liftgate myself for my D90.