fuel sensor

[izzi]

While waiting for carb parts to arrive I thought I should attempt to repair fuel gauge fault on my midget.
( fuel gauge goes straight to full when ignition is switched on and stays there until you turn it off even if tank is low) when you remove the cable from the sensor it still reads full.
I have removed sensor from fuel tank ( all under safe conditions )
The problem I have is what is the best and simple way to check what is at fault. (have checked and cleaned earth connections)
It could be that the previous owners connected wires incorrectly
The black and green wire on the left of the gauge seems to go to the tank sensor yet at the sensor end the wire looks pale orange.
Photo of gauge attached[frame][/frame]

[mogbob]

Izzy
Now the Sender unit has been removed from the vehicle safely , get out your multi meter.
Away from the car.
Set it to Ohms and clip / touch one lead to the lucar connector and the other to the body of the sender.
You should get a reading and it should re-act / move.. as you move the float arm through it's full travel.
Low resistance should register with the float lifted to it's highest point ( registering a full tank ) and high resistance
should register when the float is allowed ( slowly !! ) to drop to it's full extent, signifying an empty tank.

If it registers correctly on the Multi meter then the sender is OK.If the "earth" contact through the bolts/ screws connecting sender to the fuel tank is clean, all should be well with the sender end.

Wiring colours..check with your workshop manual wiring diagram first , typically from the back of the fuel gauge it should be Green/ Black from the "T " for tank connection and Green on the "B" for battery connection.As you say, it might well be that the previous owner has been "dabbling" with the wiring set up.
If the Green / Black wire..... due to a fault.... " shorts /earths " along the way, the gauge would show "full ".

I would trace the pale orange wire at the sender end, back to the gauge.I hope that you will find the problem somewhere along the route.Dodgy connection... not soldered / no insulation tape,wire chafed, etc.You will recognise it when you see it !!

( Original wiring would soon disappear into the loom, whereas the bodge job will probably run loose through the boot area, down under the carpet in the passenger compartment and up behind the dash ).

Bob

[izzi]

Thanks, Bob.

Done the test as advised and the sender registers correctly on the Multi Meter. I did ensure the tank end was earthed,but will ensure that it is refitted properly.
Now it is time to follow the wires.

When I check the live green wire to the Circuit Tester the test light keeps flashing,disconnected live wire to fuel pump and the flashing stopped (test light remained on)
Oddly enough there was 2 wires bodgely connected to the live end on the fuel pump.

got to admit it is starting to become quite interesting. ( fuel well out of reach just in case )

I have not got a manual, I am using the Lucas Wiring Colour Guide which agrees with you.

[blues2rock]

Hello Izzy, if the gauge remains on 'full' even with the connection removed at the tank unit (ignition on) then the most likely fault is the wire leading to the tank unit is chaffed and earthing out somewhere along its length. OR the gauge has an internal fault.

To check for internal fault just set your meter to ohms and ensure that there is no continuity between either gauge terminal and the gauge casing (disconnected and 'off' the car of course).

If the gauge passes as above just run a long jumper wire from the tank unit to the sender side of the gauge. (make sure you make the connection to the tank unit first - and remove it last to avoid any sparks. It should be perfectly safe with ignition off but given your 'extra' wires best to be on the safe side)

If you then get a reading that roughly agrees with your tank contents it 'proves' the fault lies in the harness and it will be time to start unwrapping to find the short.

Hope this helps.

[izzi]

Thanks blues2rock,
Now done fuel gauge test, and it is working,
Just got to find where the wire problem is on the loom etc;.
Roy,

[mogbob]

Roy
Well done so far...you're on the home straight now ! Trace that pale orange ....like a bloodhound on a mission....you'll find it.
Bob

[izzi]

Roy
Well done so far...you're on the home straight now ! Trace that pale orange ....like a bloodhound on a mission....you'll find it.
Bob

Problem now solved.
This was a mission that shows how bad some people are out there.I think.
The bodge using various wires was as follows:
The green and black wire that should come from the gauge to tank sender was connected from the gauge to the earth on the fuel pump then live wire from the fuel pump to sender.

Thanks for all your help on this one.
Roy

[mogbob]

Roy
RESULT !!
Putting it all to bed correctly... the fuel pump should just have two connections...White / power feed and Black to the earth point.
I'd check over the rest of the "loose wiring" to see if there are any other bodges on the vehicle.
Well done.
Bob