1972 Chrysler gas gauge always reads full

[NWPT70]

Hello,

The gas gauge needle on my 1972 Chrysler New Yorker always goes straight to full when the ignition key is turned on regardless of the tank capacity. Does anyone have any input on why this could be? I notice there was a capacity of some sort that was mounted behind the cluster that was not connected.

Thanks

 

[MrMoparCHP]

Unplug the sender at the tank and see if it drops to E, if it does then you have a bad sender, if not there is a short in the system or maybe a bad gauge. Does the temperature gauge seam to work ok?


Alan

 

[NWPT70]

Thanks for that input. I do not have a temperature gauge on this car, only a temp warning light.

 

[oliver]

does your sending unit have its ground strap? I had a fuel gauge problem once because of this

 

[NWPT70]

does your sending unit have its ground strap? I had a fuel gauge problem once because of this

View attachment 139510

I will surely check!

 

[bluefury361]

does your sending unit have its ground strap? I had a fuel gauge problem once because of this

View attachment 139510

This link completes the ground between the sender unit and steel fuel line, jumping the rubber connector hose. If it's present make sure its clean.

 

[NWPT70]

This link completes the ground between the sender unit and steel fuel line, jumping the rubber connector hose. If it's present make sure its clean.

Can this strap be accessed without dropping the tank?

 

[MrMoparCHP]

Can this strap be accessed without dropping the tank?

Yes, just slide under and look where the fuel line connects.

Alan

 

[ceebuddy]

If the ground strap/clip was missing or bad, there would be too low a reading or the needle would maybe even stay at "E".

If you unplug the cable at the sender (at the tank) the needle should drop to "E". However, this does not necessarily mean the sender is at fault. It could still be that the 5V dash voltage limiter is not working right and producing too high a voltage. Since it is only there to feed the gas gauge in your car, you can't compare as was suggested (i. e. with a temperature gauge reading).

To further pinpoint the problem you could check the resistance of the sender with an ohmmeter. Unplug the wire from the sender, hold one cable of the ohmmeter to that pin and hold the other cable of the ohmmeter to the round sender/hose base plate. The reading should be somewhere between 73 ohms (tank empty) and 10 ohms (tank full).

I don't think the gauge itself is bad. They are fairly simple, with a heating wire wound around a bimetallic strip that moves the needle. I don't think that if supplied with correct voltage anything within the gauge could lead to the needle constantly indicating a full tank. It is more common for this type gauge to die due to the heating wire burning through and then the needle will stay at "E".

Also make sure there is no short somewhere in the wire going from the gas gauge to the sender. In the trunk the wire is the only one going to the middle of the car and then disappearing through the trunk floor there. Check the insulation of the wire for any cracks that could produce a short when touching the body.

 

[NWPT70]

If the ground strap/clip was missing or bad, there would be too low a reading or the needle would maybe even stay at "E".

If you unplug the cable at the sender (at the tank) the needle should drop to "E". However, this does not necessarily mean the sender is at fault. It could still be that the 5V dash voltage limiter is not working right and producing too high a voltage. Since it is only there to feed the gas gauge in your car, you can't compare as was suggested (i. e. with a temperature gauge reading).

Thanks for this great info. Immediately after reading this I drew a red flag. I do not believe I have a 5 Volt dash voltage limiter. Would it look like a capacitor connected by a wire? If so where does it connect to? The positive terminal on the gas gauge?

 

[ceebuddy]

I would think your car does have such a voltage limiter since the gas gauge needs a constant reference voltage so as not to fluctuate with actual alternator output voltage (the latter changes for a moment if you step on the brakes or turn on the headlights).

The voltage limiter is a small squarish metal box plugged into the back of your gauge cluster, the location of which should be somewhat similiar as seen on this picture:

The round thing you see there is a capacitor to suppress ignition noise for a better radio sound, not a resistor.

There are eletronic versions of the voltage limiter available nowadays and should be preferred if the need for replacement arises. This Allpar article is recommended reading on the voltage limiters.

 

[MrMoparCHP]

If there is no small squarish metal box plugged into the back of your gauge cluster then the voltage limiter is in the gas gauge.

If the gas gauge has three terminals then it is in the gas gauge.


Alan

 

[tbm3fan]

How about the fact that it is 45 years old and Chrysler didn't expect this car to be around 45 years later. Probably will be internal issues inside the actual sender.

 

[73Coupe]

I have erratic and /or non-accurate gas guage readings, even with a new sender. Using the FSM to troubleshoot the problem, it seems to be the voltage limiter that's bad. I read up on this at Allpar and it seems that these limiters in the instrument cluster were not that reliable: Vintage Chrysler electrical repairs and updates (part 2)
Doing a little more research, there are a few sources that sell new solid-state limiters.
Has anybody ever used these people: Real Time Engineering RTE limiter - rte

Looking under my dash last night, I couldn't see any silver box plugged into the printed board. I did notice a spot where it could be plugged in, though, and thought, what the hell...where is it? Maybe it's way up in there where I can't see. I was hoping I could change it without removing the cluster. The FSM states that one can by lowering the steering column.
Does anybody have any photos of the back of their cluster?

Thanks, 73

 

[CanCritter]

bad ground.....