Fuel gauge stopped working

[data89]

1969 C10 Stepside, 7 gauge panel. All of a sudden my fuel gauge stopped working in 18 years without having done any work on it. Stuck at 3 o-clock.

Have made the usual checks...grounded tank wire with ign on and gauge needle went ccw down like it should. So gauge is working, right. With tank wire on and ign on I get 8.4 volts at the tank and 8.4 volts at the spade connector in the fuse box, so no short in the wire. And, the connection to the dash panel must be good to get the voltage at the spade connector. Am I looking at a bad sensing unit in the gas tank? Is there a trick getting that out?

[franken]

The sender is probably bad. The removal process is pretty obvious once the seat is out of the way.

[Getter-Done]

Originally Posted by data89

1969 C10 Stepside, 7 gauge panel. All of a sudden my fuel gauge stopped working in 18 years without having done any work on it. Stuck at 3 o-clock.

Have made the usual checks...grounded tank wire with ign on and gauge needle went ccw down like it should. So gauge is working, right. With tank wire on and ign on I get 8.4 volts at the tank and 8.4 volts at the spade connector in the fuse box, so no short in the wire. And, the connection to the dash panel must be good to get the voltage at the spade connector. Am I looking at a bad sensing unit in the gas tank? Is there a trick getting that out?

Here is a short video for the process of removing the locking ring that holds it in place.

How To Remove A Fuel Sending Unit From A Gas Tank...

[mr48chev]

It might sound crazy but you want to make sure that the gas level is way below the sending unit. I've had people fill their gas tank on the way to the shop to have me pull the tank to work on it.

[data89]

Originally Posted by mr48chev

It might sound crazy but you want to make sure that the gas level is way below the sending unit. I've had people fill their gas tank on the way to the shop to have me pull the tank to work on it.

Guessing from the travel I have taken it should be about 2/3 full. What happens if that is too high...why the caveat?

[data89]

Originally Posted by franken

The sender is probably bad. The removal process is pretty obvious once the seat is out of the way.

good, thanks.

[data89]

Originally Posted by Getter-Done

Here is a short video for the process of removing the locking ring that holds it in place.

How To Remove A Fuel Sending Unit From A Gas Tank - YouTube

Great to see this. It should be similar to a back of seat tank, I would imagine.

[data89]

Originally Posted by franken

The sender is probably bad. The removal process is pretty obvious once the seat is out of the way.

I have buddy bucket seats, so it should be pretty easy.

[data89]

Okay...after doing further checks, my fuel gauge is still stuck at 3 o-clock. Last check on sender, ign off ohm meter on sender wire to ground shows 33.4 ohms. Now, if I rock the truck the ohms bounces around a little bit, indicating to me that the float/sending unit is working. Can I assume the sending unit is okay?

[pjmoreland]

Originally Posted by data89

Okay...after doing further checks, my fuel gauge is still stuck at 3 o-clock. Last check on sender, ign off ohm meter on sender wire to ground shows 33.4 ohms. Now, if I rock the truck the ohms bounces around a little bit, indicating to me that the float/sending unit is working. Can I assume the sending unit is okay?

Did you have the sender wire unplugged from the fuse panel when you took this measurement? It needs to be unplugged from the fuse panel in order to get a valid Ohm measurement of the sender.

[data89]

Originally Posted by pjmoreland

Did you have the sender wire unplugged from the fuse panel when you took this measurement? It needs to be unplugged from the fuse panel in order to get a valid Ohm measurement of the sender.

No I didn't. I'll do it that way this time. Thanks.

[data89]

Circuit is open... spade connector (removed)/sender terminal to ground. No ohms no voltage, ign on or off. Ground is good from gas tank to body.

With circuit in play, I have 8.4 volts to ground from sender terminal or spade connector, ign on.

So, I would assume the sender is bad. What bothers me is I have 33 ohms with the circuit in play, ign on, and when I rock the truck the sender ohms varies, indicating that it is responding. Yet my gauge remains at 3 o-clock.

[pjmoreland]

Is the sender round base flange that attaches to the tank well-grounded?

[data89]

Originally Posted by pjmoreland

Is the sender round base flange that attaches to the tank well-grounded?

I checked grounds for everything, but, I'll double check that again right now...

Okay, just checked battery ground to cab and battery ground to sender base flange and it's good.

Would seem like next step is to take the sender out.

[data89]

Sender is out...how do I test it with a volt/ohm meter?

I get no resistance reading, pos to grnd when I move the float arm. Is that resistor on the sending unit the problem? Actually I do get a reading of 14-15 ohms at the bottom of travel if I put a little pressure on it. but 0 ohms moving the arm up regardless of where I put pressure.

By the way, when the sender was in the tank, I only had 8.4 volts at the terminal. I've been thinking there should be 12v. Yes, No? Or is that due to the resistor on the gas gauge?

[pjmoreland]

The voltage measured at the sender terminal is affected by the resistor on the back of the gauge as well as the two windings inside the gauge. With a functioning sender, the voltage would change depending on the position of the sender arm.

You should be getting 0-90 Ohms through the sender (isolated from the rest of the system) depending on the arm position. Based on your readings, that sender appears to be dead. You could try moving it back and forth a bunch to see if it comes back around. The original sender that's in my truck was flaky at first after reviving it from a 24-year nap, but now it works fine.

[data89]

I fixed it! Thank you everyone for your input. I now know all there is about my gas gauge and float assembly. Float assembly resistor was not working. Pried the tabs and opened it up. Wires were corroded so contact tab was not making contact. Cleaned them up with emery paper, reassembled and voila, everything working as it should. Over the years I have found this to be the best website for valuable information from members. Thanks again.

[Getter-Done]

Glad to here this.