Fuel gauge Help

[Larr991]

Have a 53 COE truck that I'm having problems with the fuel gauge, hopefully someone can lead me in the right direction. The ending unit was shot, so I replaced it with a new one the same kind. Checked the gauge as described in the repair manual, and works as outlined. When I hook everything up, the fuel gauge goes to full, even though the sending unit is at empty, when I move the sending unit to full, the gauge goes to about a half of a tank. Any ideas on what the problem could be? thanks for any help! 

[Sniper]

Sounds like it's working backwards?  Is this still running 6 positive ground or has it been converted?

[Larr991]

Yes, still positive ground. The truck only has 11,000 original miles on it. Yes, it seems backwards, but will not go past the 1/2 mark. Don't think I've ever seen this before. Do you think the dash gauge is bad?

[lostviking]

Did you manually move the float to simulate a full tank? If not, maybe it's getting stuck mechanically and only moves to half way. What tests have you performed? Have you measured the voltage that is going to the gauge?

[Larr991]

Yes, I did move the float. When it's on empty (the float) it reads full. When I move it to full it goes to a half tank. Just strange. I didn't measure volts to the gauge but have tested with test light.

[billrigsby]

Here is a thread from earlier this year that may help;

 

Fuel gauge difficulties

[Larr991]

Ok, Thanks. I did do the test described in the manual, worked as it should. I'm puzzled over this. I have the same sending unit that was in it. This is on a big truck, with saddle tank just so you know.

[Merle Coggins]

Have you measured the resistance values of the new sender over the full range of movement? It should be around 10 Ohms at the full position and around 90 Ohms at empty. It sounds as though the resistance values may be reversed and too low. 

[Larr991]

Ok, I'll try it. Thanks!

Edited December 2, 2021 by Larr991

[Larr991]

Ok, I did the ohms test, around 5 empty, 28 full. any idea what I do next?

[Merle Coggins]

Get the correct sender

[Larr991]

So you are saying this is not the correct sender for the system, correct?

[Merle Coggins]

Yes, that's what I'm saying. As stated earlier the fuel level sender should have 10 Ohms of resistance at the Full position and 90 Ohms at Empty.  Yours has 5 Ohms at Empty and 28 Ohms at Full. The resistance swing is backwards and the values are too low. The lower the resistance value from the sensor the stronger the electro magnet in the gauge will be to pull the needle to the Full position. 

[Larr991]

Ok, Thanks for the help. I'll try getting another sender. Thanks again, I'll keep you posted on how I make out.

[JBNeal]

additional information - fuel level sending unit upgrades

[MBF]

I bought one for each of my trucks this past year off eBay from MoParpro.  Good seller, they’re the proper ohm rating, and work as designed.

 

[SCD]

 

I HAD THE SAME PROBLEM WITH MY 55

REPLACED WITH DORMAN 55818 UNIVERSAL UNIT THIS WAS THE RIGHT OHM FOR THE GAUGE.

THE DORMAN UNIT DIDN'T FIT IN THE OPENING OF THE TANK SO I MODIFIED IT .  I HAD TO GRIND OFF A LITTLE OF THE CIRCUMFRENCE OF THE UNIT TO FIT THE TANK AND MAKE THE FLOAT ARM THE RIGHT LENGTH.   WORKED GREAT   STEVE

[dcotant]

I bought one of these but the ohms range was 32 to 235.  Yours was 10 to 90 ?

[B1B Keven]

Dorman 55815  Product Specifications

Gasket or Seal Included:	Yes
Module:	No
Ohms Empty:	240
Ohms Full:	33
Package Contents:	Fuel Pump Kit
Package Quantity:	1
Packaging Type:	Box
Plug/Connector Type:	Spade/Ring
Pump Included:	No
Terminal Quantity:	1
Terminal Type:	Spade/Ring
Wiring Harness Included:	No

   

[Larr991]

Thanks for all the info. The opening in the tank is small, but sure I can modify one to fit. I did look at the Dorman,but are you saying the Ohms range was to high?

On 12/14/2021 at 4:33 PM, dcotant said:

I bought one of these but the ohms range was 32 to 235.  Yours was 10 to 90 ?

 

[dcotant]

Yes was too high for my 49 and as per specs provided above by Keven. 660 ohms in parallel should get it to the right range however.

[Larr991]

Ok, Maybe I'll try the MoParpro and see what they have.

[B1B Keven]

F-203-4853 Fuel Sending Unit

https://dcmclassics.com/search?controller=search&orderby=position&orderway=desc&search_query=sending+unit&submit_search=

 

[Larr991]

Ok, thanks, that looks correct. Just have to get some measurements from them.