What do you mean by 'the sender is controlled via the ECU'? Which ECU? You've got half a dozen (or more), one of which J285, is the 'control unit in dash panel insert', the big, wide grey box in the diagram I posted. Wired direct to the gauge sender. Dash panel insert is the clocks unit, behind the steering wheel. (Well, in front of it really, I suppose)

 

Edit: what you should do, is get your trusty multimeter, switch it to the lowest Ohms range, and measure from pin 2 of the (unplugged) loom connector for the fuel pump (the pin that the white/brown wire goes to) to something that's definitely connected to chassis ground (pin 4 will probably do if you can't find anything else easily to hand). If it's more than a small handful of Ohms, you need to trace that wire to wherever it goes and clean the connection where it does earth to the body. 

What do you mean by 'the sender is controlled via the ECU'? Which ECU? You've got half a dozen (or more), one of which J285, is the 'control unit in dash panel insert', the big, wide grey box in the diagram I posted. Wired direct to the gauge sender. Dash panel insert is the clocks unit, behind the steering wheel. (Well, in front of it really, I suppose)

 

Edit: what you should do, is get your trusty multimeter, switch it to the lowest Ohms range, and measure from pin 2 of the (unplugged) loom connector for the fuel pump (the pin that the white/brown wire goes to) to something that's definitely connected to chassis ground (pin 4 will probably do if you can't find anything else easily to hand). If it's more than a small handful of Ohms, you need to trace that wire to wherever it goes and clean the connection where it does earth to the body. 

I meant the main ecu, i thought the fuel sender went pump> dash> ECU>dash>pump. Im probably wrong, but thats what i thought. But i will try the test you suggested 20k is the lowest on my multi meter 

Edited 11 April, 201511 yr by FromTheDarkness

The fuel sender is controlled by the dials. Its based on a constant current circuit.

If you pull the sensor pin on the dials to ground or to 12 volts it wont go empty to full as the circuit isnt based on that.

Easy way to test the dials is to fit a 470 ohm potentiometer wiper to the gauge signal pin and one side of the potentiometer to ground. Then adjust the pot and watch the dial go up and down. Thats how i worked it out on Bossfoxes FGF

On my vrs i had a number of fuel gauge issues all resolved by replacing the alternator (faulty regulator ) cleaned battery terminals and fitted a new battery.

In short the fuel gauge is very sensitive to poor joins and low battery voltages. again i saw that if i turned the key on it would say half start the engine and it would rise to two thirds.

The fuel sender is controlled by the dials. Its based on a constant current circuit.

If you pull the sensor pin on the dials to ground or to 12 volts it wont go empty to full as the circuit isnt based on that.

Easy way to test the dials is to fit a 470 ohm potentiometer wiper to the gauge signal pin and one side of the potentiometer to ground. Then adjust the pot and watch the dial go up and down. Thats how i worked it out on Bossfoxes FGF

On my vrs i had a number of fuel gauge issues all resolved by replacing the alternator (faulty regulator ) cleaned battery terminals and fitted a new battery.

In short the fuel gauge is very sensitive to poor joins and low battery voltages. again i saw that if i turned the key on it would say half start the engine and it would rise to two thirds.

Are you saying that a bad earth would not make the gauge reverse? ie showing full when empty

 

I read that bad earth does this, as if earth is removed then the sender receives a fluctuation in power..

Just to add ive had the dash out and all seems fine, checked all wires going into the pink connection nothing loose, tried wiggling with ignition on no change, all looks immaculate behind there, no sign of any corrosion or water. I took the back plate off and no sign of any damage to components, i used electrical cleaner on it all. No change. I havent tested anything with the multi meter as ive left in my locker at work.

 

Im guessing its damaged on route, my guess would be back of the car, maybe damage from the old seal leak.. which where not done on my car so 13 years of leaky backside lol ....

 

to be continued :P

Are you saying that a bad earth would not make the gauge reverse? ie showing full when empty

 

I read that bad earth does this, as if earth is removed then the sender receives a fluctuation in power..

I won't pretend to speak for Taylor93 cos he clearly knows more about how these work than I do; but looking at the circuit in the wiring diagram I posted, if the earth is completely disconnected, then no current at all can flow through the sender potentiometer, so whatever the gauge says in these circumstances would stay the same no matter what the fuel level does.  If the earth connection was just high resistance, rather than completely broken, things get more complicated. Not sure I could predict how that would affect the gauge.

 

Edit: What's confusing me now that I think about what you've done, is that you say you've had one or two gauge senders working correctly when not installed in the tank, yeah? Which suggests to me that the wiring must all be OK? I think? :S   << Is that the smiley for confused?

I won't pretend to speak for Taylor93 cos he clearly knows more about how these work than I do; but looking at the circuit in the wiring diagram I posted, if the earth is completely disconnected, then no current at all can flow through the sender potentiometer, so whatever the gauge says in these circumstances would stay the same no matter what the fuel level does.  If the earth connection was just high resistance, rather than completely broken, things get more complicated. Not sure I could predict how that would affect the gauge.

 

Edit: What's confusing me now that I think about what you've done, is that you say you've had one or two gauge senders working correctly when not installed in the tank, yeah? Which suggests to me that the wiring must all be OK? I think? :S   << Is that the smiley for confused?

No i saw them working, but didnt realise what way the float was being pushed, so both act the same, so when full it shows empty, and empty shows full on the guage

No i saw them working, but didnt realise what way the float was being pushed, so both act the same, so when full it shows empty, and empty shows full on the guage

Hi There, read this thread with great interest due to a fuel gauge issue myself. (nowhere near as fraught as yours). Have you got it sorted?

This fault can be the contacts on the wires where they clip in on the float slider assembly they are meant to be pressing against the contact but I have found they needed bending back to make the gauge work again. After sorting it check with ohm meter as operating slider float  .

 

The diesel pipes have a push in ring on the base , push in and pull up at the same time.

 

The electrical contact plug you have to put a small screwdriver in the slot and push down while pulling up to get off. 

The sender track is a variable resistance. At one end of the track it will read 0 ohms(full tank),and at the other end a resistance of say 100 ohms(empty tank), this value varies with manufacturers. If you have a reasonable  multimeter you should be able to check the continuity of the sender track.It does'nt have to be a 'Fluke'.There are a lot of  other good multimeters out there at  sensible prices.