Patrol 4.2 D

Yep, this worked on the brother in laws, although I have heard yo may need an hour or so for the computer to reset. Aparently when the fault is not caused by the earthing, it can be caused by leaving the tank empty for extended periods. The computer shuts down the system rather than run the pump dry for a few seconds every time you start up. Will gladly stand corrected on this one though.

The brother in law didn't fill the sub tank often, only on big trips. To me it would be better to have fuel in the tank all the time, generally, if I've gone to the trouble of stopping at the servo, I may as well fill the thing up so I don't have to come back for a while...

Cheers Andrew

As the owner of a '99 4500 petrol GU, I also suffered this problem on one occasion, when the car was only a few months old. Took it to the stealership (no, not a typo) and the solution was to disconnect the battery for I think about 15 minutes.
I have not had it happen again.
Much later I was advised to always keep at least some fuel in the sub-tank as the computer runs the pump for approx 5 secs every time the car is started, and the pump can be damaged by dry running.

I've done 2 pumps. Pulled one apart to see why they were failing and they are not constructed like a normal pump. These pumps have a circular solenoid with a metal tube that runs through its centre. In the metal tube is a sliding metal tube with a one way valve on it and a spring. The whole operation is controlled by a circuit card which pulses the solenoid when the sub tank is activated. This draws the valve tube towards the inlet where it picks up fuel when the solenoid is energised. When the solenoid relaxes the valve tube springs back bringing a small amount of fuel with it. The cycle is repeated and you end up with a trickle of fuel going into the main tanks filler hose.

The pump was very difficult to dismantle and is filled with spacefill foam. I haven't tested the solenoid or circuit board yet to find out what is failing but probably wouldn't bother due to the hassel it took to get it apart.

Mine has failed again so I will now use either an aftermarket rotary pump or pressurise the tank with a couple of PSI from the compressor and valve arrangement which will be the easiest and cheapest solution. Will also be the most reliable as well.

Regards
David

I agree.

To diagnose a faulty pump, the best way to check is turn the sub tank pump on when the car is running and open the fuel filler to the main tank. If you can see fuel coming in then all OK. If not put your hand on the sub tank fuel pump. You will feel it vibrating when energised in which case it is OK and you have a priming/airlock issue. If no vibration then disconnect the plug to the pump and use a multimeter to measure the voltage from the Sub Tank ECU. Should be 12V accross the 2 pins when switched on. If there is voltage then pump is dead. I also connect 12v to the pump iteslf from a power supply to further check.
Be careful with petrol cars when doing the latter as sparks may result.

Only do the above checks when you have cleared the light and reset the Sub tank ECU by disconncting the negative lead to the battery and then reconnecting. The ECU will not show a light for a dead pump - only a problem with the ECU itself or power issues (as is the case when connecting certain turbo timers which cause the ECU to go into sulk mode).

Regards
David