4.2tdi Fuel tank problems

[pwacka8]

Hello All
I have an issue were my 4.2tdi can only run on the first half tank of diesel ,once the needle goes below half way the car cuts out , fill her up with diesel again and shes off.

I had an issue with the car were it wouldnt start ,looking back it all points to the fuel being below half way , because the car ran without issue for the first half tank.

I have been looking into the way the fuel tank is constructed and also the operation of the 2 fuel pumps.

It looks to me like the fuel in the left hand side of the tank is never being used , when i fill up im actually just filling the right hand side which shows on the gauge as full , once all the fuel in the right hand side is used it cuts out.

Why is the fuel from the left side not being used???


There seems to be a bit of confusion on the net over which is the main pump and which is the transfer pump.

It looks like the right hand is the main and the left is the secondary.

Does anyone know the correct operation of these pumps and which does what , i would rather replace one pump than both.

Which one does the transfer of fuel between the tanks??

Is this how it operates??

Thanks in advance

PWACKA8

[pwacka8]

Forgot to say , i know the tank has half a tank left in as after it cut out on the motorway on me when it was reading just under half full i could only get another £40 worth of fuel into the tank.

[mattylondon]

I'm guessing you may have a faulty suction jet pump.

This is my evaluation from the details you've gave us and my understating of how the fuel supply works. Our cars have two fuel pumps. One fuel pump constantly feeds the engine. When more fuel is needed, i.e. higher engine speed, both fuel pumps feed the engine. The fuel tank does have two sides and under normal driving one fuel pump will be working and emptying its side of the tank more quickly. To compensate for this and to balance fuel evenly there is a suction jet pump that delivers fuel one side to another. This, I'm guessing, may be faulty as you do have fuel remaining in your tank.