Sub tank question

[Jvertigo]

Hi everyone,

I bought an Australian import 1993 80 series 4.2 HDJ80 with a 1HZ engine (based in the UK). It has the factory sub tank fitted. Looking if it from underneath, the sub tank looks like it runs straight to the engine, once you have pressed the sub tank button on the dashboard.

Is this standard for the diesel? Is there a filter from the sub tank, or does it pass through the main fuel filter in the engine bay?

As I understand it, on the petrol version, the sub tank feeds into the main tank once the button is pressed.

Neither sub tank or main tank gauges seem to work; the main tank gauge used to work, but I cannot find the reason for it it working now: fuses are good.

Any information on how these run please!!!

 

[chapel gate]

The sub uses the main fuel filter.

 

[GeekOKent]

HDJ with a 1hz ?

 

[Jvertigo]

HZJ. It was early o’clock

 

[Cruiserfan]

Hi all, this system underneath your car with the OEM twin tanks consists of many parts and functions like this:
In the fuelline system there are two 3way valves. If you drive on your main tank, then the excess of fuel from the engine goes back into the main tank.
If you use the sub tank switch, your engine will use the fuel from the sub tank, (so you drive on your subtank) , and then the excess of fuel goes back into the subtank.
Please see attached file, hope to be of help.

 

[Jvertigo]

That’s absolutely great, thank you

 

[Cruiserfan]

If you feel the subtank switch does not work, you have to check all the electrics, means not only the fuses and/or the switch, but also underneath the car, the 3 way valves, are these functioning ?
Next to that you have to be sure that there are no air leaks in the fuel suction system, the small fuel suction tubes on top of both tanks can be a problem, mostly rust.
The 3 way valves: fuel supply is the 77710-60030, which is in the attached picture, and the return valve is the 77720-60020, which has connections in a smaller diameter.
I assume you have checked that the in-tank suctions filters are in good condition, and not clogged up ?