Discovery1 Fuel return path pls

[Chasesdragons]

Hello,
I do not have a trustworthy reference for Discovery 1 200tdi 1991.

I am trying to trace the fuel path, pressure and flow rates in the machine - can you guys help please?

Does anyone know what the fuel pressure is to the mechanical lift pump attached to the OS engine? (I think it is a negative figure as the lift pump SUCKS the fuel from the tank..)

What is the pressure and flow rate of the fuel lift pump? If it felt that there was a high enough fuel pressure in front of it (i.e between in and the filter, lets say). Does it stop pumping? (common sense says yes...but)

How many fuel returns are there after the Fuel Injection pump? Someone said 2 - is this true??? Basically one returning unused fuel from before the injectors which is quite a heavy flow and a SECOND smaller one that is called a injector leak off pipe which is a dribble and possibly highly aerated?

Warmest Regards
Udhi :D

[TEMPL4R]

The lift pump that is on the side of the engine block works by the camshaft moving the arm and pulling down on the diaphragm. That draws fuel in from the tank ( atmospheric pressure actually pushes it, but that's physics) then a spring pushes the diaphragm up and sends the fuel to the filter and injector pump. When the system is full, the spring can't push, so you get the loose priming handle when you bleed the system. It's the same for a petrol engine when the carb if full and the float shuts off the valve. On a constant feed system, you usually have an electric pump and a fuel return.

Depending on the manufacturer, you can have 1 or 2 returns to the tank, most feed the injector leak off into the return at the filter or a tee piece in the return line.

Unless it's a Vauxhall diesel, they feed the leak off into the pump feed, but as the injection pump draws fuel from the tank, any problem with the pipes or the seals on the top of the injectors means the car won't start when left for a few hours, air gets in and the fuel syphons back to the tank. It also draws engine oil into the fuel system and burns it. A sign is oil in the fuel filter and tank and using oil quite quickly.

Chris

[Chasesdragons]

Thanks Chris,
With particular reference to the 200Tdi. What would happen if the fuel return was plumbed back into the feed? (creating a LOOPED FEED)

To maintain standard pressures, I would assume it gets T'd just AFTER the FUEL LIFT PUMP? Rationale being that the lift pump senses a higher pressure in the system and doesn't allow fresh fuel in until an equal amount of "Post Lift Pump" fuel is used up by the engine, causing the fuel pressures to drop? <did that make sense, will it work??!)

Does anyone know the fuel pressure where the Lift Pump stops operating and/or the fuel pressure in the return pipe line?

Reason for all this is to create a twin tank Veg oil system. I need a way to keep the VO and DERV apart. I need to try and keep the VO as hot as possible, and it is going to get hot whizzing thru the injectors etc.

[lynalldiscovery]

I used to know a nice man that converted trucks to run on red and white! and he used the closed loop system.

I would just have said both returns to before the lift pump and before that a t piece with either supply plumbed in.

Reason before lift pump as the pump output pressure is prob higher than the return line pressure..

I do know that it causes lots of bother if you run out of fuel in a closed loop as its a toss to get rid of the air.

You can buy twin switching valves that make sure the correct fuel is returned to the correct tank on e-bay i think.



Lynall