Fuel Gauge

[DavidThorn]

The car is a late BJ8, suddenly the fuel gauge has deflected to full, and beyond.

I have taken the cover off the sender unit. All seems OK the float is moving properly the "probe" is about halfway along the coiled wire resistor which is correct as the tank is about half full. The sender unit has a good earth.

Have pulled the dial out of the dashboard, but seems connected properly and it has a good earth.

Every connection I check, apart from earth obviously, is giving a full 12-volt reading.

Any ideas?

David

 

[Bob_Spidell]

This is for MG gauges, but I believe it applies to any Smiths. I think the first thing you want to do is check the resistance of the sender.

Fuel gauge function - a

MGA petrol gauge troubleshooting

 

[Jerry]

and if your float is plastic, see if it is full of fuel.

 

[mezy]

If you look at the wiring diagram below. you should have a solid green wire comming from fuse 4 to the terminal B on the gauge.
Then a green / black off terminal T going to the sender unit.
If you disconnect the green / black wire from the gauge, the gauge should drop to empty.
If not there should be a black ground wire on the gauge for the light, disconnect it, if the gauge drops then it is earthing through the
case of the gauge and is Faulty.
If it does drop to empty, then the gauge is good.
Disconnect the other end of the green / black wire from the sender unit. the gauge should go to empty, if it does then there is a problem
with the sender unit.
If the gauge stays high then you have an issue with the green / black wire grounding somewhere.

 

[DavidThorn]

OK ,thanks everyone, I will check those things.

David

 

[Goldie]

If memory serves me, check that the wire from the sending unit is not grounded. I think the it will show full if grounded at the sending unit ( essentially zero resistance). Maybe something has shorted the connection to the sending unit in the trunk.

 

[DavidThorn]

Thank you so much for your assistance.

I followed the guidance of Mezy and the diagram, everything checked out as ok , I reconnected it all and the gauge seems to be working normally.

Perhaps there was a fault or perhaps just a bad connection somewhere which when re connected was sorted.

Anyway a result !!

David

 

[mezy]

Thank you so much for your assistance.

I followed the guidance of Mezy and the diagram, everything checked out as ok , I reconnected it all and the gauge seems to be working normally.

Perhaps there was a fault or perhaps just a bad connection somewhere which when re connected was sorted.

Anyway a result !!

David

I love it when a car fixes itself, do do do doo...... do do do doo.

The machines I look after at work, mostly made by a company from holland, MOBA, can break down. I can spend a couple of hours checking sensor signals are going back to the PLC, testing for wiring faults, bad windings in three phase motors, and air leaks on rams, and find nothing, only to have them start back up and work fine.

And that's another MOBA mystery.