Not sure that I understand completely what are you asking.

Did you just brim your tank as it was empty, and gauge needle rise slowly while you were driving, or your tank is full, and while engine was not running, needle was down, and starting to raise when you started the engine?

 

The fact that the gauge moves suggests that the sender in the tank is working correctly.
If your gauge reads half full and you put fuel in does gauge go DOWN??

The plugs to the pump/sender unit only fit one way so if it reads in reverse then it sounds like the wires have been cut and connected the wrong way round.
Have a look at the wires coming from the tank area and see if you can see any suspicious joints.

Edit.. just read roverlikes response ... The gauge does take a little while to rise when you put fuel in - it is not instant.

 

Thanks for your replies guys. I picked the car up and the gauge was reading 1/2 full/empty. I called in a petrol station and brimmed it. The gauge then read empty when I started driving. Gradually whilst driving, the gauge worked it's way up towards the full end. After 100 miles I decided it best to brim the tank again just to make sure I did have fuel in the tank. Again, whilst driving, the gauge started off on empty, and by the time I got home, another 100 miles, the gauge had worked it's way towards the full end. I did suspect that for some reason the wires may have been switched round, I just wondered why, as it has been owned by an elderly lady, who's husband is renovating three vintage cars and four motorcycles, so I would have thought he would know what he was doing. I will have a check of the wiring and see whether anything has been cobbled together wrong.

 

OEM fuel gauge is designed in way to show approximate amount of petrol inside the tank even when the engine is off. It should not drop to 0 unless tank is empty.
If your fuel gauge drops to 0 when the engine is off, I would imagine something was changed on the original setup.

 

sounds like either its a bad connection or the resistance in the mechanism in the tank is not able to provide a quick response.. i.e the level mechanism in the tank is faulty..

you can test the gauge.. without the fuel tank plug connected.. its a variable resistance.. so its ohms law your dealing with.. if you understand that.. its easy..

?

you provide the gauge with a voltage.. and it reads what that is.. the voltage is 0 to 5 volts, full scale.. and that is available at the fuel gauge plug.. volts in/volts out across a variable resistance.. - the fuel tank mechanism.. you know how to read ohms?

of importance is the level stored at last switch off, since that may be diifferent to the current value that will be set - after a few moments..
if it isnt.. then either the gauge in the tank is faulty or the ecu is taking a long time for ( an unknown reason ) to establish the new reading..?

ive yet to determine the influence of the ecu on that.. its probable the ecu has no influence.. and so the error might be the damper?

if its a fuel tank , not a gauge problem... bad news in store to fix it i think.

 

Hi Incony. Read ohms? I can read books! but ohms hmmm.. I think I might look for faulty wiring first. Thanks for trying.

 

Sorry, should have confirmed again. The gauge is NOT slow to react to fuel level, it is working in the complete opposite way it should, ie, empty when tank is full, then full when I have used most of the fuel.

 

so.. looking at the manual description of how it works.. what do you - and i think is wrong, and as has been suggested so far..?

wired up backwards?

 

The tank and sender and pump etc are accessed under the rear of the hood where the engine cover plate is. There is a round plate next to the engine cover held on with 4 bolts. Remove these (or 3 of them) and look at the top of the pump/sender unit. Check the wires coming out of the connector and work forwards towards the front of the car.
The reversed connection could be anywhere. Also check behind the instrument panel - maybe some 'Heath-Robinson' engineering was carried out in this area.

Good luck!
I have only seen this once in over 40 years of messing with cars.
The loom had been cut under the car and rejoined - badly.

 

Yes, thanks for confirming that it may be wired back to front. As you say, it could have been a mistake whilst working on something else. Will let you know what the outcome is, just in case there is another similar request before another 40 years passes.

 

at least, ronecc, you have supplied the answer to " just in case "

 

You are dead right.. i think i was having an off moment.. thanks for correcting me..

the electric cct diagrams are found here:
http://www.mgrover-online.com/?p=273

 

Are we talking about the modern TF here?

 

Are we talking about the modern TF here?

I would suggest that with a references to another 40 years passing and a Smiths Instrument we are talking about the original style TF from the 50's.

 

Original TF?? Good point.
However, he does refer to a modern TF in another post

Quote "I too have just purchased a TF, but mine is an '02 in BRG."

But 'Smiths instrument' ?? Is the gauge on the 02 TF made by Smiths??

 

In case of OEM MG TF fuel gauge you have only three wires - power wire from fuse box, earth wire and wire passing info from fuel tank.

On Connector C233 pin 13 you have Green/Black wire coming from sender, and on connector C230 pin 7 you have Green power wire from fuse box while on C230 pin 9 black wire provides earth connection. I would say that in case power wire and earth wire are connected in wrong way you would have much more problems.

On following picture you have diagram how fuel sender is connected. As said above only two wires are present.