200 Quattro Wagon L5-2226cc 2.22L SOHC Turbo (MC) (1989)
Fig. 41 Control Pressure/Altitude Graph
Incorporated in the warm up regulator is an aneroid (a sealed capsule containing a measured amount of a gas, usually nitrogen). The aneroid is sensitive
to changes in atmospheric pressure. As atmospheric pressure decreases, the aneroid expands against the diaphragm, via the pushrod. Fuel flow back to
the tank from the control plunger is restricted. This increases the pressure on top of the control plunger (resisting motion of the sensor plate to reduce
deflection) and leans out the fuel mixture. The aneroid can increase the warm control pressure from 3.6 bar (52 psi) at sea level to 4.5 bar (65 psi) at
1750 meters (5250 feet), Fig. 41.
An additional bi-metallic spring holds the aneroid compressed when the engine is cold to avoid a lean mixture during warm up at high elevations.