Engine: Locations
Components On The Engine
Front view
Designation
1 - Injection valve
2 - Temperature switch for engine temperature
3 - Tensioning element (camshaft adjuster VarioCam)
4 - Hall-effect sensor
5 - Knock sensor
6 - Oil temperature sender/oil level sensor
7 - Knock sensor
8 - Tank vent (fuel evaporative valve)
9 - Individual coil/spark plug connector
10 - Tensioning element (camshaft adjuster VarioCam)
11 - Hall-effect sensor
12 - Temperature sender (coolant)
Function of components
1. Injection valves
The valve coils consist of brass and have an internal resistance of approximately 12 Ohms. The injection valves are activated sequentially, and the electrical leads therefore must not be swapped. The change in the quantity injected is controlled by the DME control module via variable valve opening times.
2. Temperature switch for the engine compartment fan
An NTC thermistor is installed between the intake pipes of cylinders 1 and 2 in order to measure the engine compartment temperature. The DME control module activates the engine compartment fan depending on the respective engine compartment temperature and various additional factors.
3. Tensioning element (camshaft adjuster VarioCam)
In order to increase torque and improve cylinder charging, the engine is equipped with two VarioCam drive links installed in the chain tensioners of the camshafts.
The two drive links are actuated via solenoid valves, which are in turn activated by the DME control module.
4. Hall-effect sensor
A plug-in Hall-effect sensor is installed in the cylinder head at the 3rd cylinder of cylinder bank 1 - 3 in order to detect the ignition TDC of the 1st cylinder. The Hall signal is produced by a rotor fastened on the inlet camshaft of cylinder bank 1 - 3.
In addition to detection of ignition TDC of the 1st cylinder and the associated allocation of injection signals (sequential), ignition signals (stationary high-voltage distribution) and knock-sensor signals (knock regulation), the Hall signal is also used for diagnosis of the VarioCam system in the Boxster.
5. Knock sensor
Function
If the knock-sensor voltage, in combination with an amplification factor calculated by the control module, reaches a maximum voltage threshold, the DME control module interprets this as "knocking". When knocking is detected, the calculated ignition timing angle is retarded by a crankshaft angle of 2.25° at the corresponding cylinder (cylinder selective). The maximum retardation per cylinder depends on the engine rpm and can be up to 15 °crk behind the nominal ignition timing angle.
When knocking is no longer detected, the ignition timing angle is returned to its optimum value in small increments.
Safety function
If the DME control module detected a fault on knock sensor 1, knock sensor 2, the Hall-effect sensor, or an error in calculation of the engine load signal, the DME control module will retard the calculated ignition timing angle by 9 °crk as from the condition "Knock regulation active" and as from a fixed engine and intake air temperature.
6. Oil temperature sender
The DME control module uses the oil temperature to calculate the switching rpm for the VarioCam system. The oil temperature sender and oil level sender form a single component that is screwed into the crankcase.
7. Knock sensor
See Item 5.
8. Fuel evaporative valve
A solenoid valve is installed in the line between the intake housing and carbon canister. The flow direction of the one-way valve is stamped into the plastic housing. The valve is fitted below the intake pipe for cylinder 5.
The fuel evaporative valve is closed when de-energised. When the ignition is switched on, the DME control module applies positive voltage to the fuel evaporative valve via terminal 54. When the engine has started and the operating conditions listed beside this column have been reached, the fuel evaporative valve is connected to ground by the DME control module as well (but via terminal 61) and opens.
9. Individual ignition coil
The individual ignition coil and the spark plug are connected via a spark plug connector with an internal resistance of approx. 2.5 kOhms. The individual ignition coil is provided with positive voltage (terminal 3) and negative voltage (terminal 2) via the electrical lead on the keyed 3-pole plug contact. Terminal 1 on the individual ignition coil leads to the ignition driver. The coils are energised when the injection, ignition and oxygen-sensor relay is closed.
10. Tensioning element (camshaft adjuster)
See under Item 3.
11. Hall-effect sensor
See under Item 4.
12. Engine coolant temperature sensor
The engine temperature sender is designed as a double NTC thermistor. The control module uses the temperature sender signal to calculate the injection signal during the warm-up phase in order to enrich the mixture when the engine is started, to calculate the ignition timing angle during the warm-up phase and to control the electric fans. One temperature-dependent resistance (resistance measured between contacts 2 and 3 in the connector housing) provides the signal for indication of the engine coolant temperature in the instrument cluster, and the other temperature-dependent resistance (measured between contacts 1 and 4 in the connector housing) informs the DME control module about the coolant temperature.
The engine coolant temperature sensor is screwed into the coolant guide housing.
Rear view
1 - Secondary air pump
2 - Vacuum reservoir (only on Tiptronic and OBD II)
3 - Overflow valve
4 - Check valve
5 - Vacuum valve
6 - Check valve
7 - Throttle part
8 - IACV (idle speed positioner)
9 - Throttle potentiometer
10 - Hot film mass air flow sensor with intake air temperature sensor
11 - Oxygen sensors ahead of the catalytic converter
12 - Oxygen sensors behind the catalytic converter
13 - Pulse sender (reference mark sensor/rpm sender)
Components No. 1, 3, 4, 6, 12 are installed only on OBD II vehicles.
1. Secondary air fan
USA vehicles are equipped with a secondary air system in order to reduce pollutants in the exhaust gas during the warm-up phase and to fulfil the emissions limits. An electric air pump is mounted on the body in the engine compartment for this purpose. It is activated by the DME control module and, via air lines, injects the secondary air behind the exhaust valves.
2. Vacuum reservoir
Ensures the function of vacuum-operated components.
3. Pneumatic switch-over valve
A pneumatic switch-over valve is fitted between the air pump and exhaust valve. It is closed when the secondary air system is inactive and thereby prevents the induction of additional air as a result of flow conditions.
4. Check valve
5. Vacuum valve
6. Check valve
7. Throttle plate part
8. IACV (idle speed positioner)
A two-winding positioner that is screwed directly to the throttle plate part without additional air guide hoses.
9. Throttle potentiometer
The throttle position is determined via a potentiometer fitted on the throttle-plate shaft. The DME control module supplies the potentiometer with a controlled voltage (5 V). Depending on the position of the potentiometer (throttle-plate angle), there is a greater or lesser voltage drop across the potentiometer. The DME also recognises the smallest opening angle of the throttle via the voltage drop or the corresponding current. This is defined as the "idle position".
10. Hot film mass air flow sensor
A new hot film mass air flow sensor with the designation HFM 5 is used on the Boxster. Its housing shape permits installation in one direction only. It is fastened with M 5 Torx screws. As with the previous mass air flow sensors, the manufacturer performs laser calibration on the new HFM 5 in a so-called "master tube". In other words, a corresponding air mass produces an exactly defined voltage signal.
The hot film mass air flow sensor is fitted in the air cleaner housing at the outlet of the air cleaner. The operating voltage range is 9 - 7 Volt, and the output voltage of the mass air flow sensor (voltage to the DME control module) lies between 0 and 5 Volt. The actual measuring element is supplied with a controlled voltage of 5 Volt from the control module in addition to the voltage supplied by the vehicle electrical system to the mass air flow sensor. This prevents fluctuations in the vehicle voltage, e.g. when loads are switched on, from influencing the measuring process.
Intake air temperature sensor
The intake air temperature sensor is installed in the mass air flow sensor housing and is thus located in the intake air flow. It is supplied with voltage by the DME control module via terminal 43, and is connected together with the HFM 5 on the ground side. The intake air temperature sensor functions according to the NTC principle. The DME control module uses the signal from the intake air temperature sensor to calculate the substitute load signal if the mass air flow sensor fails. The load calculated by the control module, which depends on the throttle potentiometer, is corrected by the IATS signal. A negative correction is applied to the substitute load signal at high air temperatures.
At the same time, the decreasing air density is compensated. Furthermore, the risk of knocking increases with increasing intake air temperature. The ignition timing is therefore retarded at a high engine temperature (> 90 °C) and high intake air temperature (> 30 °C).
11./12. Oxygen sensors
These sensors are floating, i.e. the DME control module connects ground to the oxygen sensors. The sensors are located in the exhaust-gas flow ahead of the catalytic converter; two sensors are additionally installed behind the catalytic converter on OBD II vehicles.
Oxygen sensor heating
Besides being heated by the exhaust gas, the oxygen sensors are also heated electrically. For this purpose, the oxygen sensor, injection and ignition relay is activated and applies positive voltage to the oxygen sensor heaters after operation of the DME relay.
The DME control module connects ground to the heating resistors.
13. Pulse sender (reference mark sensor/ rpm sender)
The DME measures the crankshaft rotation with an inductive sender. A pulse wheel is mounted on the flywheel for this purpose. This pulse wheel is a toothed ring stamped from sheet steel and spot-welded on the flywheel. It has 60 teeth. A gap produced by the omission of two teeth is defined as the reference mark and is located
84° ahead of TDC of the 1st or 4th cylinder. The pulse sender is fitted in a bore on the crankcase. The distance is not adjustable.