Diesel Models

At high altitudes (above 4000 ft.), solenoid valve closes or engages and fuel pressure builds up between it and pressure control valve. As soon as pressure (acting on both sides of the valve) equalizes spring force, the altitude compensation valve closes slightly. This causes less fuel to be returned to pump inlet.

When less fuel is returned, pump pressure increases (which moves injection timer piston), and roller cage turns in the opposite direction to the cam disc. The disc them moves up onto cage earlier than usual (fuel injection takes place earlier).

At low altitudes (below 4000 ft.), solenoid valve is open or disengaged. Fuel is returned to pump inlet by means of 2 feedback channels; control valve and solenoid valve, and a channel beneath control valve.