Fuel, Exhaust & Engine Electrics
Page 2.22
Ignition System
General
The ignition systems used in the V6 and V8 engines largely correspond
to the systems used in previous engines. The ignition system map in the
DME control unit has been designed to meet DFI specific requirements.
V6 DFI Engine
Knock Sensors
One knock sensor is bolted to the crankcase on the left -KL- and
another on the right -KR-. They detect knocking in individual cylinders.
To prevent knocking, the cylinder selective knock control system
monitors the electronic ignition timing control system. Based on the
signals from the knock sensors, the DME control unit adjusts the ignition
timing angle for the knocking cylinder until the knocking stops.
If a knock sensor fails, the ignition timing angles of the affected cylinder
group (1-3-5 or 2-4-6) are retarded. This means that a safety ignition
timing angle is set to “late”. Knock control for the cylinder group of the
remaining, intact knock sensors is unaffected. If both knock sensors fail,
the DME control unit goes into knock control emergency operation
during which the ignition timing angles are generally retarded, thereby
reducing engine power considerably and increasing fuel consumption.
Ignition Coils – V6
The V6 engine still has static high-voltage ignition distribution with indi-
vidual ignition coils directly on the spark plugs. The DME control unit
activates the individual ignition coils individually in the firing order 1-5-3-
6-2-4 for each cylinder. The individual ignition coils in the Cayenne V6
have an integrated output final stage, but unlike the Cayenne V8
engines, the diagnostic function is integrated in the Motronic control
unit. If an ignition coil fails, fuel injection for the affected cylinder is
deactivated. This can happen on up to two cylinders.
Spark Plugs
The V6 engine has air gap spark plugs with one ground electrode, which
must be changed every 36,000 miles (60,000 km) or after 4 years
according to the Technical Manual.
Note
Spark plug replacement intervals have changed for M.Y. 2008 when
compared to the 2003-2006 Cayenne models.
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