Function Of Components; Injection Valves; Temperature Switch For The Engine Compartment Fan; Tensioning Element - Porsche Boxster Technical Manual

Boxster DME diagnosis 24
8
Function of components
1. Injection valves 4. Hall-effect sensor
The valve coils consist of brass and have an inter- A plug-in Hall-effect sensor is installed in the
nal resistance of approximately 12 0. The injec- cylinder head at the 3rd cylinder of cylinder
tion valves are activated sequentially, and the bank 1 -3 in order to detect the ignition TOC of
electrical leads therefore must not be swapped. the 1st cylinder. The Hall signal is produced by a
The change in the quantity injected is controlled rotor fastened on the inlet camshaft of cylinder
by the OME control module via variable valve bank 1 -3.
opening times. In addition to detection of ignition TOC of the 1st
cylinder and the associated allocation of injection
signals (sequential), ignition signals (stationary
high-voltage distribution) and knock-sensor sig-
8 2. Temperature switch for the engine nals (knock regulation), the Hall signal is also
compartment fan used for diagnosis of the VarioCam system in the
Boxster.
An NTC thermistor is installed between the intake
pipes of cylinders 1 and 2 in order to measure
the engine compartment temperature. The OME
control module activates the engine compart- 5. Knock sensor
ment fan depending on the respective engine
compartment temperature and various additional Function
factors. If the knock-sensor voltage, in combination with
an amplification factor calculated by the control
module, reaches a maximum voltage threshold,
the OME control module interprets this as "knock-
3. Tensioning element (camshaft adjuster ing". When knocking is detected, the calculated
VarioCam) ignition timing angle is retarded by a crankshaft
angle of 2.250 at the corresponding cylinder
8 (cylinder selective). The maximum retardation per
In order to increase torque and improve cylinder cylinder depends on the engine rpm and can be
charging, the engine is equipped with two Varia- up to 150 crk behind the nominal ignition timing
Cam drive links installed in the chain tensioners angle.
of the camshafts. When knocking is no longer detected, the ignition
The two drive links are actuated via solenoid timing angle is returned to its optimum value in
valves, which are in turn activated by the OME small increments.
control module.
Safety function
If the OME control module detected a fault on
knock sensor 1, knock sensor 2, the Hall-effect
sensor, or an error in calculation of the engine
8
24 01 Diagnosis/Troubleshooting DME 24 -D 13
Printed in Germany -4, 1996 98624D1