The TD5 fuel system is GRIM, and the way it is arranged in the cylinder head is a disgrace.
The fuel pump in the tank is really TWO pumps, low and high stages.
The low stage sucks fuel from the tank, drives it through the filter (located OUTSIDE the car behind the rear right roadwheel - LUDICROUS) and the fuel then goes to the high pressure stage which drives it towards the engine.
There a pressure limiting valve on the rear end of the cylinder head keeps the pressure to about 4 BAR / 60psi, and feeds this into the fuel gallery that runs the full length of the inside of the head AND BACK OUT AGAIN at the front. Left-over fuel from the limiting valve returns to the tank. This involves a LOT of fuel being pumped.
The lower ends of the injectors are fully fitted into the fuel gallery, and I mean clean THROUGH from top to bottom, and are surrounded by fuel at 4 BAR.
Injection pressure is generated by mechanical means - a piston INSIDE each injector, driven by a rocker and camshaft lobe. Each injector piston is hit full-stroke every time. Engine control (throttle) is achieved by an electronic spill-valve that releases MOST of the fuel in the injectors back into the gallery - and that fuel is VERY HOT as a result. A little fuel is injected at extremely high pressures into the combustion chamber.
Everyone who owns a TD5 (or TD4) engine should find a diagram of what seals the injectors and thus the fuel into the gallery and keeps the fuel separated from two places, (1) the engine oil sump, and (2) the cylinder combustion area.
Your entire engine depends on a lousy copper washer under each injector, and a O-ring around each injector body. If gas leaks past a copper washer, you are STUFFED. The clamp thing that holds injectors down is a disgrace. It looks like a lash-up idea, like the placing of the fuel filter.
It is a DIY job to fix injector washers and O-rings, but some care and attention is required. I had to do mine at 35k miles, a month ago.
CharlesY
