Passat L4-1984cc 2.0L DOHC (9A) (1990)
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Fuel Pressure Regulator: Description and Operation
CIS-E Fuel Pressure Regulator
Fuel Pressure Regulators
The CIS-E Motronic Fuel Pressure Regulator, mounted on the side of the fuel distributor, maintains a constant "system" pressure in the fuel distributor.
System pressure is set by fuel pressure deflecting a diaphragm in the regulator. When the fuel pump is running, fuel pressure builds until it overcomes
spring pressure in the regulator and moves the diaphragm. This opens the regulating valve which returns excess fuel to the fuel reservoir and keeps the
fuel pressure at the specified level. The Fuel Pressure Regulator has three fuel lines and a vacuum hose connected to it. The fuel line with a large banjo
fitting (mounted to the side of regulator) is the fuel pressure supply line from the fuel pump. The fuel line with the smaller banjo fitting (also mounted to
the side of regulator) is the fuel return line from the differential pressure regulator. The third fuel line (mounted to the bottom of regulator) is the fuel
return line to the fuel reservoir. The vacuum hose (mounted to the top of regulator) is vented to atmosphere at the air cleaner.
