Fuel gauge help

[mattdus]

my fuel gauge registers between empty and 1/4 no matter the amount of fuel in the tank. I grounded the wire at the sending unit and the gauge went to full, checked the sending unit and got a reading of around 48 ohms (which as I understand it should be about a half tank. Tried running a ground from the sending unit to the chassis and got nothing still registers at the same point. If I understand everything correctly (which I likely dont) the first test says the gauge and everything there is good while the second tells me the sending unit should be good. where do I go from here?

 

[67Dart273]

Well the sending unit could be stuck, the thing to do is wait until it's nearly MT and ohm the thing, then fill it 1/2 way and recheck, and then fill it and recheck.

I know that's lots of trouble, the alternative is yanking the sender/ tank.

I just found this, the old Miller gauge tester is alleged to be: (model C-3826)

L = 73.7 Ohms (empty)
M = 23.0 Ohms (1/2)
H = 10.2 Ohms (full)

NOTICE that the 1/2 way resistance is NOT "linear" that is, is not halfway between the high and low

You have four basic possibilities:

The gauge is screwed up (inaccurate)

The sender is screwed up (rusty, sticking, bent/ sinking float, etc)

The wiring is poor, poor connections, etc

The VR is irregular

If you buy some good heavy wirewound resistors the same value as the miller tester, you should be able to sub them back at the sender and check the gauge for accuracy

 

[mattdus]

Thanks, sounds like I may have a stuck up sending unit. I have never pulled one and dont like the idea of doing it but that may be what I need to do. I will check the ohms again once I have driven some gas out of the tank and see what I get.

 

[RedFish]

Replacing the sender on these cars is childs' play compared to some others. After reading your post, I wouldn't crawl under the car without a new sender in hand.
One tip, The new sender will include a new seal and locking ring. Throw the new locking ring away and reuse your original locking ring with that new seal.

 

[66plyValiant]

sounds like the float for the fuel gauge may have a hole in it and no longer floating anymore thats what happened in my case

 

[mattdus]

Replacing the sender on these cars is childs' play compared to some others. After reading your post, I wouldn't crawl under the car without a new sender in hand.
One tip, The new sender will include a new seal and locking ring. Throw the new locking ring away and reuse your original locking ring with that new seal.

Thats my plan, got to run the tank if gas out then I will get into the sending unit. Does the tank need to be dropped to change it or will I need to drop the tank?

I dont have a problem with using the old ring, just wondering, I assume the new ones don't line up right?

we will see whats up with the sending unit in a week or 2, I will be going out of town this week to meet my son for the first time!

 

[70orangeswinger]

I just changed one on a 68 Dart without dropping the tank and I found out the hard way that the reproduction locking ring just wasn't up for the task.

 

[cudajim]

Well the sending unit could be stuck, the thing to do is wait until it's nearly MT and ohm the thing, then fill it 1/2 way and recheck, and then fill it and recheck.

I know that's lots of trouble, the alternative is yanking the sender/ tank.

I just found this, the old Miller gauge tester is alleged to be: (model C-3826)

L = 73.7 Ohms (empty)
M = 23.0 Ohms (1/2)
H = 10.2 Ohms (full)

NOTICE that the 1/2 way resistance is NOT "linear" that is, is not halfway between the high and low

You have four basic possibilities:

The gauge is screwed up (inaccurate)

The sender is screwed up (rusty, sticking, bent/ sinking float, etc)

The wiring is poor, poor connections, etc

The VR is irregular

If you buy some good heavy wirewound resistors the same value as the miller tester, you should be able to sub them back at the sender and check the gauge for accuracy

67dart, I really do appreciate your responses but coming from you I am actually surprised you would say "ohm the thing"? Is that a technical term? More correctly you may want to say "check the resistance with your ohm meter". Ok, I'm done with my rant!