Evaporative System Pressure Leak Diagnosis. Overview - BMW 5251 Service Manual

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Fuel Injection
Evaporative system pressure leak
diagnosis, overview
The M62 TU engine is equipped wlth an evaporative fuel sys-
tem pressure leak diagnosis system. The main component of
this system is the leakdiagnosis pump (LDP). The function of
the LDP is to pressurize the fuel tank and the evaporative
emission system for the purpose of detecting leaks.
This system iscapable of detecting a lealcas small as0.5 mm.
The LDP, located in the left rear wheel housing, contains the
following:
Vacuum chamber.
Pneumatic pump chamber
DME activated vacuum solenoid
Reed switch (provides switched voltage feedback signal to
DME).
The vacuum supply line is in the wiring harness from the en-
gine compartment and runs down the driver's side of the vehi-
cle.
The canister vent valve is ~ntegrated into the LDP, which
IS
electrically controlled by the ECM. The canister vent valve is
opened to provide fresh air entry into the fuel system only dur-
ing purge operation.
-
Purge operation characteristics:
Off idle through full throttle: purge valve opened by pulse
width modulated (PWM) control of the ECM. PWM duty cy-
cle varies by engine operating conditions (e.g. warm idle,
purge valve opened slightly; cold idleldecel with engine
temp < 67" C. purge valve always closed).