fuel gauging issues

hi,
Hoping with all your experience you can help me.
I have recently purchased a 1986 landcover 110, the fuel gauge permanently reads full - previous owner says he replaced gauge and sender and did not fix it.

I have carried out some investigation on the fuel sender and established that it is functioning correctly.

I have measured resistances at the sender of 57ohms when about half full and 17 ohms full.

The gauge installed is a PRC 3107 and under a 300ohm load reads 3/4 full and under a 1k load just under 1/2 full, empty at 2k ohms.

This leads me to believe I have an incorrect part no gauge fitted as resistances dont match those of the sender.

The parts catalog calls up PRC7313, I am reading online however that these two are interchangeable, is this correct? If so I would be ordering another with the same issue. and does anyone have any other suggestions?

It depends where the previous owner bought the replacement sender, quite a few are duff straight out of the box. My replacement series sender tells me I have more petrol the further I drive it. A full tank read between half and three quarters full, when I get down to half a tank, the gauge says full, then it starts to go down again but stops moving at quarter full. I can't be arsed changing it again so I just go be the tripometer

Col

There is deffo a missmatch there ...

If the gauge needs 1KR to read 1/2 full and the sender is 17R them it's going to read full all the time.
Sounds like you need additional resistance on the gauge, bridge the 12V terminal and the blue/green wire terminal, with a 127R resistor.
https://cpc.farnell.com/tt-electronics-welwyn/rc55y-127r-0-1/resistor-0-25w-0-1-127r/dp/RE05782

Colthebrummie said:

It depends where the previous owner bought the replacement sender, quite a few are duff straight out of the box. My replacement series sender tells me I have more petrol the further I drive it. A full tank read between half and three quarters full, when I get down to half a tank, the gauge says full, then it starts to go down again but stops moving at quarter full. I can't be arsed changing it again so I just go be the tripometer

Col

Click to expand...

I have a similar issue with my series where the tank is empty when the gauge read 1/4. I also use the trip meter and reset after every fuel up.

OP, it might be worth bench testing the gauges and sender together so both are out of the vehicle and you can test with known good wiring and see what readings you get. Although my fuel guage works and does what you would expect I would still say it is more of a guide than accurate and even on my defenders I use the tripometer to measure mileage rather than the guage. Very roughly my swb series will get 200miles from a tank, the defedner 90 with get 300 miles, and the 110 will get 450.

miktdish said:

There is deffo a missmatch there ...

If the gauge needs 1KR to read 1/2 full and the sender is 17R them it's going to read full all the time.
Sounds like you need additional resistance on the gauge, bridge the 12V terminal and the blue/green wire terminal, with a 127R resistor.
https://cpc.farnell.com/tt-electronics-welwyn/rc55y-127r-0-1/resistor-0-25w-0-1-127r/dp/RE05782

Click to expand...

thanks. I was thinking along these lines. would this work though as the gauge would need 2k to read empty but the sender about 120?