daddy2coull

Active Member

• Oct 31, 2019

• #1

I’ve had my 90 for about five years but the fuel gauge has never worked.

to try and cut a long story short and eliminate any wiring faults I’ve made a test rig out of the 90. Trouble is I can still only get the gauge to work in reverse when it works at all. I have a new level sender and the old one I took out but both have exactly the same fault. Is there anything inside the gauge that could cause this symptom?

 

Europa486

Well-Known Member

• Oct 31, 2019

• #2

The majority of fuel gauges and sender units work on a resistance system,
That is with a full tank of fuel the sender unit shows maximum resistance to the gauge so the gauge will show full,
When tank is empty then minimum resistance will show empty, so earthing out the sender feed wire should show a full tank on the gauge,
If it doesn’t and you know you have good continuity on the wire to the gauge then it can only be the gauge or possibly the instrument panel ballist resistor, my money is on the gauge or wiring on the gauge as it’s very unlikely
That two sender units will have the same fault,

 

daddy2coull

Active Member

• Oct 31, 2019

• #3

On the new sender I have 9ohms at full and 325ohms empty

 

daddy2coull

Active Member

• Oct 31, 2019

• #4

It’s not showing a ballast resistor on the wiring diagram. Any idea we’re I would find it or should it be in the gauge itself?

 

zeaphod

Well-Known Member

• Oct 31, 2019

• #5

Have you tried reversing the connections at the gauge?

 

Europa486

Well-Known Member

• Oct 31, 2019

• #6

The ballast resistor is usually on the back of the instrument panel, it gives the gauges 9 volts instead of 12 volts
So even with a flat battery the gauges will be accurate,
Pop out the gauge and run a direct feed and earth to it to establish if it’s working in the correct sense,
From the ohm reading it seems to need minimal resistance to read full, that’s counter intuitive to the normal operation of fuel gauges,
Are the gauges original equipment? If they have been changed they may not be compatible with the sender units you have, it still looks like the gauge is the culprit,

 

Europa486

Well-Known Member

• Oct 31, 2019

• #7

 

Europa486

Well-Known Member

• Oct 31, 2019

• #8

The schematic above shows the normal operation on your car,

 

daddy2coull

Active Member

• Oct 31, 2019

• #9

Yep. That’s what I’ve Jerry rigged up. It’s still works in reverse Both level senders give the same ohms readings low resistance at full high resistance at empty.

 

daddy2coull

Active Member

• Oct 31, 2019

• #10

I tested the fuel gauge,if I earth out the output it shows full

 

Last edited: Oct 31, 2019

daddy2coull

Active Member

• Oct 31, 2019

• #11

Anyone else have any suggestions?

 

Europa486

Well-Known Member

• Oct 31, 2019

• #12

Is your sender units britpart supplied? I know of one that arrived duff, have you a photo of the connection on
The sender unit,
If all the earths are good and you got continuity from the sender to the gauge, and the gauge has checked out ok then though improbable it points to the sender units,
If the resistor in the sender units have been wired incorrectly that would explain your ohm meter readings,
I would try and find a known working unit and check the ohm reading on that and compare to yours,
Good luck

 

daddy2coull

Active Member

• Nov 1, 2019

• #13

Whatever I’ve tried I’m still getting reverse ohms readings on my sender and the gauge. I’ve ordered a genuine sender and oem gauge From lrdirect. I’ll keep you posted in case someone looks in the future.