Fuel Gauge

[bstock1962]

Originally Posted by mister.freeze

That measurement was installed. Incidentally, with the tank nearly empty, the needle started to move whenever I stopped. It would go down to around 3/4 then work it's way back past full as things settled down. I put in 10 gallons and it's locked back at 1/2" past full. Safe to say the resistor is bad, and the float and arm actually work.

After adding 10 gallons of gas, what is your resistance measurement now? When you pull the sending unit out again, you'll want to measure the range looking for 0-90 ohms.

[mister.freeze]

34.7 after 10 gallons and 25 miles. Maybe my tan wire is adding resistance along the line?

[bstock1962]

Originally Posted by mister.freeze

34.7 after 10 gallons and 25 miles. Maybe my tan wire is adding resistance along the line?

So virtually no change after adding 10 gallons of gas. Are you measuring at the tank/sending unit, or at the fuse box with tan wire disconnected and measuring wire back towards tank?

[mister.freeze]

At the sending unit, tan wire still attached, and grounding stud where jumper from the flange is connected to the frame.

[bstock1962]

Originally Posted by mister.freeze

At the sending unit, tan wire still attached, and grounding stud where jumper from the flange is connected to the frame.

You have to disconnect the wire at the sending unit before measuring. If you don't, I believe you are measuring the sending unit and the fuel gauge in parallel. That's probably why your last measurement didn't change much.

If it's easier, you can measure at the fuse box by disconnecting the tan wire from the fuel terminal (located at the top of the box). Measure the end of the wire (which goes back to the tank) and the other lead to a known good ground.

This is all to confirm what we already suspect, that the sending unit is bad.

[mister.freeze]

That explains why the 2 readings were so similar.
With the tan wire disconnected, I get 133 Ohms. Obviously, I shouldn't get more than 99, and that should be on a full tank. My guess is corrosion between the resistor and the terminal on top of the sender. I wonder why the needle movement the other day with sloshing gas...?
I'm going to order a new sender this week, so next time I drop the tank I can either fix mine or replace it and be done!

[bstock1962]

Originally Posted by mister.freeze

That explains why the 2 readings were so similar.
With the tan wire disconnected, I get 133 Ohms. Obviously, I shouldn't get more than 99, and that should be on a full tank. My guess is corrosion between the resistor and the terminal on top of the sender. I wonder why the needle movement the other day with sloshing gas...?
I'm going to order a new sender this week, so next time I drop the tank I can either fix mine or replace it and be done!

Sounds good. While you have it out, take some resistance measurements of the bad sending unit. Try drenching it with engine degreaser and see if cleaning the varnish off changes the resistance. If you can get it back to 0-90 ohms it’s fixed. Either way, keep us posted on the outcome.

[mister.freeze]

Ordered the new sender. Maybe next weekend.
Tanked up this morning; ohmed out at 124.6

[mister.freeze]

Wrong part arrived. Waiting on new sender.

[mister.freeze]

Well, Brother's didn't have the right sender for my Aero tank. I'd expect LMC and the like not to have them either. Aero wants $78...

[mister.freeze]

Gauge works now, for about the last 5-10 gallons. Still looking for the right sender for my Aero tank. Aero wants $78 plus shipping!

[C4UC101969]

Guys I've been reading over your conversation and I know its been awhile, but I just got about 1.5 months ago 69 c10 and the fuel gauge always sits on empty, when I disconnect the ground form sending unit with key on it goes to 3 o'clock, ground it to gas tank it goes back to empty. My tank is always on full and the needle just does not move at all, so my question is this is a float problem, sending unit problem or a grounding problem. Any help would be greatly appreciated form mister.freeze and bstock1962 on this issue and anyone else please. In the picture uploaded i am driving with a full tank.

[dmjlambert]

Yes sounds like the float. Go ahead and remove the sending unit and see if the float is off the arm or full of gas. See this thread. http://67-72chevytrucks.com/vboard/s...d.php?t=666161

[C4UC101969]

Originally Posted by dmjlambert

Yes sounds like the float. Go ahead and remove the sending unit and see if the float is off the arm or full of gas. See this thread. http://67-72chevytrucks.com/vboard/s...d.php?t=666161

Thank you, will get it replaced asap and hopefully it will fix the issue.

[VetteVet]

Got mine from these guys and I/m very happy with it.


https://www.partsgeek.com/catalog/19...ding_unit.html

If you have a v-8 they will send you the one with a 3/8ths line which is correct but if you had a six cylinder you probably have a 5/16ths line. I had a six originally and the v-8 ran fine but I changed all the lines to 3/8ths. I ohmed the sender and it was right on the money, 0 empty and 90 full. $34 bucks and free shipping.

[C4UC101969]

Originally Posted by VetteVet

Got mine from these guys and I/m very happy with it.


https://www.partsgeek.com/catalog/19...ding_unit.html

If you have a v-8 they will send you the one with a 3/8ths line which is correct but if you had a six cylinder you probably have a 5/16ths line. I had a six originally and the v-8 ran fine but I changed all the lines to 3/8ths. I ohmed the sender and it was right on the money, 0 empty and 90 full. $34 bucks and free shipping.

Thank you, I was hoping that you would see this thread as after reading countless threads about fuel gauges you seemed to be always on the ball with it. Appreciate it......

[66clow]

Originally Posted by C4UC101969

Guys I've been reading over your conversation and I know its been awhile, but I just got about 1.5 months ago 69 c10 and the fuel gauge always sits on empty, when I disconnect the ground form sending unit with key on it goes to 3 o'clock, ground it to gas tank it goes back to empty. My tank is always on full and the needle just does not move at all, so my question is this is a float problem, sending unit problem or a grounding problem. Any help would be greatly appreciated form mister.freeze and bstock1962 on this issue and anyone else please. In the picture uploaded i am driving with a full tank.

I'm going to chime back in because i never got mine working either. I just left it alone for a while lol I did replace my sending unit, mine is stuck on 3/4. The wires are hooked up correctly but I'm not getting anything where should I check? Is there a way to confirm that the guage is working correctly?

[dmjlambert]

Originally Posted by 66clow

I'm going to chime back in because i never got mine working either. I just left it alone for a while lol I did replace my sending unit, mine is stuck on 3/4. The wires are hooked up correctly but I'm not getting anything where should I check? Is there a way to confirm that the guage is working correctly?

C4UC101969 did a test above, disconnected wire from sending unit with key on it goes to 3 o'clock, ground wire to gas tank it goes back to empty. If the gauge works, VetteVet gives the info above for a new sending unit.

[Sparky dave]

I gave my fuel sender wire a quick touch to earth, this makes the fuel gauge go to full. At least then you will know the gauge works

[Sparky dave]

Looks like a sender unit out job, ready for some tests

[66clow]

Extending this with another question. I replaced my sending unit. Guage has never worked. I get no power at the fuse box at the tan wire with power on or off. Grounding the fuse box tan wire does nothing at the fuse box. I attached a wire from power to the fuse box tan wire and the guage goes full? Where could the problem be? Thanks

[VetteVet]

Originally Posted by Sparky dave

I gave my fuel sender wire a quick touch to earth, this makes the fuel gauge go to full. At least then you will know the gauge works

I believe the fuel gauge will go to empty if you ground the sender wire and past full if you just disconnect the sender wire.

[VetteVet]

Originally Posted by 66clow

Extending this with another question. I replaced my sending unit. Guage has never worked. I get no power at the fuse box at the tan wire with power on or off. Grounding the fuse box tan wire does nothing at the fuse box. I attached a wire from power to the fuse box tan wire and the guage goes full? Where could the problem be? Thanks

Your power to the fuel gauge comes from the fuse panel on a pink wire which runs to the no. 3 terminal on the cluster plug. Key on only.
The tan wire at the fuse panel is just a junction point for the sending unit wire to connect to the gauge. You should read 12 volts there if you have power to the gauge even though it has nothing connected. When you jump it to ground you will get current flow through the gauge to ground with no resistance which simulates an empty fuel tank. Remember the sender range is 0hms empty, and 90 ohms full.

When you put power on the tan wire you are back feeding the gauge
and it is reading through the gauge resistor to the gauge ground which deflects the needle to full. You need to concentrate on why you aren't getting 12 volts to your gauge resistor on the right hand terminal.

The power for the fuel gauge also powers the brake warning light. Try grounding the brown wire on the proportioning valve and see if the brake warning light comes on. the temperature gauge also gets power from the gas gauge but it may not move unless the coolant heats up. If it has power you could ground the temp sender wire on the engine and the temp gauge should go full hot.

What ever you do, do not put any power on the wire that goes to the sending unit into the tank. The resistor on the sender might glow and heat up enough to ignite the fumes in the tank. NOT GOOD.

[66clow]

Originally Posted by VetteVet

Your power to the fuel gauge comes from the fuse panel on a pink wire which runs to the no. 3 terminal on the cluster plug. Key on only.
The tan wire at the fuse panel is just a junction point for the sending unit wire to connect to the gauge. You should read 12 volts there if you have power to the gauge even though it has nothing connected. When you jump it to ground you will get current flow through the gauge to ground with no resistance which simulates an empty fuel tank. Remember the sender range is 0hms empty, and 90 ohms full.

When you put power on the tan wire you are back feeding the gauge
and it is reading through the gauge resistor to the gauge ground which deflects the needle to full. You need to concentrate on why you aren't getting 12 volts to your gauge resistor on the right hand terminal.

The power for the fuel gauge also powers the brake warning light. Try grounding the brown wire on the proportioning valve and see if the brake warning light comes on. the temperature gauge also gets power from the gas gauge but it may not move unless the coolant heats up. If it has power you could ground the temp sender wire on the engine and the temp gauge should go full hot.

What ever you do, do not put any power on the wire that goes to the sending unit into the tank. The resistor on the sender might glow and heat up enough to ignite the fumes in the tank. NOT GOOD.

Lol thanks for the warning. Now I know where to look, I see now why the brake warning and, temp guage is not working. I have some wire mapping to do. Thanks.