[Vwdiesel] pump effects...

[Mark Shepherd]

This is my limited view and may or may not reflect that of the experts
The piston in the pump always pumps the maximum fuel...BUT... there is a sleeve that fits outside/around the 'compression chamber' in front of the piston. This piston has a  hole down its middle that allows the compressed fuel to squirt back and it is directed to each fuel line in turn via oneway valves at the start of each line. The sleeve covers a further hole in the piston that allows spillage of fuel back into the body of the pump. The point at which this spillage occurs depends on the position of the sleeve.
The position of the sleeve is determined by several springs or links to springs pulling on it...
1) The accelerator arm...
2) The max fuel screw...
3) The centrifugal weights that are rpm relatedand also advance timing like the gas engine distributer...
4) (for the TD) the boost pressure from the turbo [which is predominantly engine loading and available exhaust heat] +exhaust flowrate to some extent also...A kind of positive feedback the rate of effect being controlled by the taper of the cone in the aneroid spring tension,and  initial position.
5) The Cold start lever I believe only advances the fuel timing and its effect  minimises as speed picks up...
Well thats my view...
Mark (The Miser) UK
"There's nothing like driving past someones bonfire and realising that its your car thats smokin' "
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