Fuel gauge issue Plymouth 1949 P18

[Thomba48]

I have this obviously not unusual fuel gauge issue: Depending on how I turn the fuel sender around the gauge either shows empty or full. But nothing in between.

 

The background:

• I am referring to my 1949 P18 Plymouth. In contrast to the P15 model my system only works with one electric cable.
• The tank was exchanged with a new one.
• The sender I have exchanged, also that would not have been necessary as I see now
• Ground have checked
• The cable between the gauge and the sender is obviously intact 

 

But still - either empty (when I turn the sender into a certain position) or full, if I turn it into another position. 

 

Any clever ideas? Should I go for a new gauge. Not difficult to find, but a very unpleasant exchange task after all. I mean getting underneath the dashboard, somehow trying to untangle the wiring, unscrewing the gauge etc. etc. etc.

 

 

thanks for your advice :-)

[Merle Coggins]

What is the actual fuel level in the tank?

Have you checked the resistance of the sending unit while sweeping the arm from ‘empty’ to ‘full’?

Is the tank providing a good ground for the sending unit? 

[Thomba48]

Thank your for having responded.

 

The tank is currently reosonably full. Which it it isn't always obviously. But with no impact on the fuel gauge level indication.

The resistance I have checked and it looks Ok to me.

Tank providing ground? How could I tell this? Fact is, the tank is new. It is properly attached to the car with the relevant straps. It is well connected to the frame, the body parts etc. So in a way, should that not suffice to provide proper ground? Or in other words, how could I improve on that front?

 

 

thanks/ thom

[Merle Coggins]

You can check the quality of your tank’s ground with a multimeter set on the ohm scale. With one lead on the sending unit body and the other one touching a nearby body panel, or bolt, it should show you close to 0 ohms. 

When I was putting my truck together I didn’t want to rely on the tank mounting points to provide the necessary ground for my sender. I added a machine screw into the body of the sending unit, where it wouldn’t interfere with anything, and added a ground wire from that screw/stud to the chassis. 

[Thomba48]

14 minutes ago, Merle Coggins said:

You can check the quality of your tank’s ground with a multimeter set on the ohm scale. With one lead on the sending unit body and the other one touching a nearby body panel, or bolt, it should show you close to 0 ohms. 

When I was putting my truck together I didn’t want to rely on the tank mounting points to provide the necessary ground for my sender. I added a machine screw into the body of the sending unit, where it wouldn’t interfere with anything, and added a ground wire from that screw/stud to the chassis. 

thank you. I shall check this and proceed as your have indicated if necessary. More thank kindest regards. Thom

[JSabah]

Following up on the ground question, I recently had my fuel tank coated (inside and out ) with the ReNu process because tanks for the ‘49 Plymouth Woody are not available- and mine was riddled with pinholes. In addition to the costing, I was planning on using some rubber between the straps  and the tank when I reinstall so obviously the tank won’t be grounded. I have the bayonet type fuel sender and don’t recall as I write this if there is a separate ground lug but if not, I like your method of adding a ground stud. My question is (and sorry for hijacking the thread a bit) but is there another reason to have the tank grounded (sparks, explosion?)? I recall being told when filling a portable gas tank (Gerry tank) to put it on the ground and not your car/trunk exactly for that reason .... just thinking I should make sure the sending unit is connected to the tank with no isolation.... thoughts?