Timing and Metering Valves

[Rawze]

basically ...

The metering actuator loads the injector up with the quantity of fuel to be put into the cylinder BEFORE each compression stroke.

The timing actuator is used to change the length of an internal piston inside the injector that causes the fuel to be put in earlier or later... and the injector is pre-loaded with this setting as well.

BOTH of those things happen when the cylinder is NOT firing yet.. when there is plenty of time to do such things, long before the cylinder fires.

When the overhead cam finally does come around on a compression stroke, the injector is crushed downwards, pushing the fuel that is already waiting in the injector, at the offset of "when" that was set by that hydraulic timing piston inside the injector.

Therefore, the injector is pre-loaded with its timing offset + quantity of fuel and waits there for the mechanical system eventually rotate around and take over.

==============
system pressures...

The fuel pressure only needs to be about 250-300 psi in the rest of the fuel system because the overhead cam itself crushes the fuel inside the injector directly... making all the actual extreme high pressures at the injector tip. The actual injected fuel pressure on a CM871 is about 28,000 - 32,000 psi as it goes into the cylinder, produced by the crushing action of the overhead cam as it pushes it down. Actual pressure does vary tough depending on rpm and other things. This is why the older ISX engines did not need a (40,000 psi) high pressure fuel pump like the newer models do.