Fuel Sending Unit Erratic

[Jocko_51_B3B]

I bought a brand new fuel gauge sending unit from one of the well known Pilothouse suppliers and decided to check it out with an ohmmeter before installing it. According to the supplier, the ohms for Pilothouse trucks should range roughly between 10 and 100 ohms as the wiper arm slides along the resistance wire. But all I got were completely erratic readings or no reading at all on my ohmmeter. I had purchased the part two years ago and the supplier wouldn't take it back so I decided to take the unit apart and see why it failed. There were two problems. First of all, the brass wiper arm was turned 180 degrees around and was making no contact with the coil of resistance wire!  I turned the arm around to make contact with the wire coil. Second, the resistance wire was so loosely wound around the white nylon insulator that when the wiper arm moved up and down, the wire would move around with it! Because the resistance wire would not stay put, of course the resistance readings were totally erratic.

 

Here's how I fixed it. First, I poked around on the loose resistance wire to try to space it out more or less evenly. Then, in order to prevent the wire from moving around, I got some crazy glue from Ace Hardware and dropped a bead along the bottom of the wire coil (opposite where the wiper arm contacts the wire of course). After that, I retested the unit and now get smooth variation from 10 to 86 ohms which should be close enough.

 

I am not sure if most sending units work this way, but if they do, poor quality control in manufacturing can definitely cause erratic fuel quantity readings from brand new sending units. Is anything made with quality in the good old USA anymore?

 

Edited May 23, 2018 by Jocko_51_B3B
spelling

[B1B Keven]

Nice fix and thanks for the 'right up'. Gotta love cheap parts. LOL

 

[Dodgeb4ya]

Chinese replacement parts are no good.... period.

Un-used MoPar factory NOS if you can find it. That's  most likely the best bet on senders  that will last and be accurate..

[Jocko_51_B3B]

I agree and if I ever find a NOS sender for sale I'll snap it up. The replacement I bought has China written all over it. For all kinds of reasons, we Americans better learn how to start making things here again.

[James_Douglas]

I have had erratic reading on NOS senders.  Fill a bucket with gas and stick it in and test it.  I had one that read off on the bench but worked fine when submerged...

[HughForrest]

These folks http://www.mykmlifestyle.com/1938_Chrysler_Fuel_Sender.html are the licensee of Atwater Kent which made them Oem back in the day. I bought one from them and am happy with it. 

[johnsartain]

On 5/26/2018 at 7:09 AM, James_Douglas said:

I have had erratic reading on NOS senders.  Fill a bucket with gas and stick it in and test it.  I had one that read off on the bench but worked fine when submerged...

Seriously? I was hoping I just didn't read that, but I have to stick my 2 cents worth in. I would hope that no one would stick anything with an electrical connection into a open bucket full of gas. All it takes is one spark to ignite the fumes and cause a fire or explosion. I wouldn't even post this even as a joke. The only reason they work without igniting the fumes in the gas tank is the density of the gas fumes and the lack of oxygen to support combustion. 

[Plymouthy Adams]

11 minutes ago, johnsartain said:

Seriously? I was hoping I just didn't read that, but I have to stick my 2 cents worth in. I would hope that no one would stick anything with an electrical connection into a open bucket full of gas. All it takes is one spark to ignite the fumes and cause a fire or explosion. I wouldn't even post this even as a joke. The only reason they work without igniting the fumes in the gas tank is the density of the gas fumes and the lack of oxygen to support combustion. 

 

I agree with the above...people, work safe out there please...enough goes wrong as it is without the need for unnecessary risks...