can anyone give a better explanation as to what he it doing with the fuel pump? am no a diesle mechanic as petrols are my thing but i do know the basics. i can cant get the grasp of what he is doing with the pump? andy one give me a better explanation???
The fuel pump has a "maximum delivery" valve which limits the amount of fuel that can be injected to JUST BELOW the point of making a lot of black smoke out the exhaust due to too much fuel for the amount of AIR the engine can suck in at atmospheric pressure.
Now, if we add an AIR COMPRESSOR PUMP, which is what the turbo is, we can create BOOST PRESSURE and stuff in about TWICE the amount of air that the engine could suck by itself, and so, as there is heaps more air, we can inject extra fuel, and make more POWER.
The snag is we must arrange the thing so that the extra fuel can only come when the BOOST PRESSURE is present, and it would be good to fix it so the extra fuel matched the BOOST which can vary a lot depending on how you are driving. Fit a boost gauge - it is fun to watch what's going on.
So on the injection pump (usually on top) is a 'plain to see' diaphragm assembly which is connected by a little plastic pipe to the inlet manifold (or turbo casing) where the BOOST pressure is, and as the BOOST pressure goes UP the pressure in the little pipe shoves the diaphragm DOWN, and that open up the maximum fuel delivery valve to suit the extra boost air.
If you increase your BOOST, you may need to increase the setting of that diaphragm to suit, that is, as extra air is available, so to will be extra fuel let through to match it.
Does that help?
CharlesY