well picked up my range today,drove back from wales about 125 miles,no probs drove good (i think)however.......filled the ga tank up to the max fuel read full but after 10-15 miles read only half full..then 10 miles or so full again and so on. after some time stoped and filled her up again £17 kept doing the same thing.. saying full then half then full..any ideas please. ps its a 4.6 2001 if that makes any diff ?

By filling the gas tank up do you mean it has an LPG system ?
If so then ignore the gas fuel guage - they are ALL bloomin useless and really inaccurate
Best way is when you fill up the gas tank then zero the trip 2 odometer and use this between fills
Fill it to the neck and see when it runs out of gas and switch over to petrol - this will give you an idea of your range on gas



Of course, if you meant petrol (as in american gas) then all of the above is bollocks............................................................

sorry v8kenny yes i did mean petrol and not LPG (my mistake) i should know if i put gas you would think LPG (thats what it is) sorry..

Hi,

Sounds like a faulty sender unit which in the P38 is part of the pump in the tank. and it is a right arse to get to. I get a similar thing with mine. I can brim the tank, but the gauge only reads half full. but as soon as i brake hard or go round a corner the gauge wakes up and reads right. It could be a simple wiring fault or a loose connection on the instrument pack.

Bryan

P38owner,dose yours read on the fuel comp when it shows half full that you have say 200 miles before fill up,then suddenly when it shows full again the comp will read say 400miles befor fill up(are they both linked ?) do they FEED of each other for info?

Hi,

The BECM, Converts a electrical resistance into a analog and digital output, the analog output is the fuel gauge dial. The digital output is for the range indicator. (this will however change depending on how you drive it and is calculated by lots of other factors) The resistance values you should be seeing are 270ohm's when empty, 19 ohm's when full. and when the system gets to 175 ohm's the low fuel warning light will come on. at this point you should have approx 9 litres of fuel left. If you can I would set up a multi meter and see what resistance values you are getting. then when it plays about see if the value changes. It sounds very much like a connection problem. You may also want to check the earth for the pump unit as well. If it helps the gauge signal wire is the green / black wire which goes to pin 10 on the BECM, the Earth for the fuel pump is in the engine bay by the main fuse box.

I think it will be one of those faults were you are going to have to check everything. i would start at the fuel pump end and work your way forward.


But back to your original question. yes mine does alter. I have fitted 3 fuel pump/sender units over the last year. due to other problems. They have all played about. Have you tried fueling yours to the top (i.e 100 litres) what does it do then. what happens if you run it right down low. does it still play about. once the fuel level drops below half a tank.

yes filled her to the very top when i picked her up..the neddle said full for about 10-15 miles then droped to half full then after about 10 more miles went to full again..
thank you for your tips i will try and do has you suggest one by one....and see what follows..