DESCRIPTION
The system used on diesel models consists of an aneroid unit, a solenoid valve and a pressure control valve (mounted in injection pump). It operates at high altitudes by advancing injection timing.
Gasoline models use a control pressure regulator combined with high altitude compensation.
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.
GAS MODELS
At high altitudes (above 4000 ft.), fuel supply is decreased in same proportion as air density. Normally, control pressure is regulated by a diaphragm and a spring. To achieve altitude compensation, another diaphragm with a spring and a chamber have been added. (Scheme 3)
Control Pressure Regulator with High Altitude Compensation. Scheme 3
The chamber maintains a constant low altitude (below 4000 ft.) pressure while pressure outside it varies according to altitude. The pressure difference causes diaphragm to exert stronger or weaker pressure on inner spring.
At increasing altitudes, decreasing pressure outside diaphragm chamber causes lower diaphragm to rise. The resulting increase of pressure on upper diaphragm increases control pressure.
TESTING
Note. Testing information not available.