Ignition System: Description and Operation
The Boxster has a modified Motronic (DME) of version M 5.2.2 to generate the injection signal, to calculate the ignition angle as well as to provide adaptive control functions for various systems and to carry out diagnostic functions.
The principal features of the Boxster's DME:
- Electronic map ignition system with permanent high- voltage distribution
- Sequential injection
- Separate fuel mixture control for each cylinder bank
- Adaptive stereo oxygen sensor control
- Potential-free oxygen sensors
- Ground-side control of oxygen sensor heating units
- Hall sensor installed in the intake camshaft for cylinder line 1 - 3
- Actuation of VarioCam valves for cylinder line 1 - 3 and 4 - 6
- New hot-film mass airflow sensor
- Intake air temperature sensor installed in hot-film airflow sensor
- Induction control with new twin-coil rotary adjuster
- Adaptive throttle potentiometer
- Adaptive knock control
- Determination of oil temperature
- New temperature sensor to determine engine temperature and to provide analog display on instrument cluster
- Engine compartment temperature sensor to control engine compartment scavenging blower
- Radiator fan control by DME controller
- Actuation and disabling of start relay
- Control of air-conditioning compressor relay
- Actuation of check-engine lamp in the case of combustion faults which may damage the catalytic converter
- Torque reduction for traction control by cancellation of ignition angle and suppression of injection
- Electronically controlled venting of active carbon canister
- Deactivation of fuel pump by airbag control module in crash
- Change of programmed idling speed for Tiptronic vehicles and selected drive position
- Reduction of torque when Tiptronic shifts gear
- Device for feedforward control when checking oxygen control loop (e.g. for exhaust-gas check)
Additional features for USA vehicles:
- Complete OBD II diagnosis with activation of check-engine lamp
- Secondary air system
- 2 additional oxygen sensors after catalytic converters
- Additional Hall sensors for camshaft for cylinder line 4-6
IGNITION SYSTEM:
The Boxster is the first Porsche model to have a permanent high-voltage distribution. As a result, the ignition distributor and ignition cables are no longer required. The ignition system is therefore completely wear-free.
The DME control unit now takes over the tasks of the ignition distributor, i.e. the calculated ignition angle (depending on the engine speed, engine load, and various correction factors) is directed, according to the firing order, by the processor to the 6 ignition units integrated in the control unit. These ignition units control the primary current circuit via the individual spark coil directly attached to the spark plugs. These ignition coils have been developed by Porsche. The control cables are labelled and attached to the compact plug connector moulded onto the housing of the ignition coil.
The connection between the individual spark coil and the spark plug is established using a spark plug connector with an internal resistance of 2.5 kohms. The electric cable and the 3-pin, coded plug contact are used to supply the individual spark coil with a positive potential (terminal 3) and negative potential (terminal 2). Terminal 1 on the individual spark coil leads to the ignition unit. The coils are supplied with voltage when the injection, ignition, and oxygen sensor relays are closed.
The technical data for the individual spark coil:
- Primary current = 7.5 A
- Ignition energy approximately 50 mJ
- Max. ignition voltage approximately 28 kV
- Isolated windings
- Housing, moulded plastic
- Compact plug connector