It might be something to do with the residual pressure in the line when you switch off. The morning I 'ran out of fuel' and had to phone the RAC, I had taken the fuel rail off the previous night to check for blocks etc. in the injectors and because the engine would not re-start afterwards I was convinced I had balsed up putting it back together (which the RAC would detect for me for nothing). It never even occurred to me that it had run out of fuel as it had been well above the 'light on' position when I parked up. After the RAC guy suggested 'theres nothing wrong here, put some fuel in it ?' it fired up at once - much to my embarassment. So I let a very small amount of fuel out but a major amount of pressure from between the tank and sensor up to the injectors.
If the pressure in the line squeezes the fuel out of the bouncy sponge ball (or does not in my case) in the tank sender unit then that may affect it's density in the petrol in the tank and hence it's height and hence the dial readout ? Of course it's equally likelly that the pressure actually helps the fuel to 'dissolve' in the bouncy ball and increase it's density and give lower reading (or is it calibrated backwards ?).
It could also be a function of the age and condition of the bouncy balls in the tank... ain't that just the truth !
I think we need a qualified Physicist familiar with the fuel system (and the bouncy balls) on the 147/156/GT to comment here ?
Last edited by rt05492; 06-10-11 at 21:47.