Part 1
Electronic Engine Controls
COMPONENT LOCATION SHEET 1 of 2
Electronic Engine Controls:
COMPONENT LOCATION SHEET 2 of 2
Electronic Engine Controls:
INTRODUCTION
The V8 4.2 Liter naturally aspirated engine is controlled by an electronic Engine Management System (EMS). The EMS controls the following:
- Engine fueling
- Ignition timing
- Closed loop fueling
- Knock control
- Idle speed control
- Emission control
- On Board Diagnostic
- Interface with the immobilization system
- Speed control
- Engine fueling
- Ignition timing
- Closed loop fueling
- Knock control
- Idle speed control
- Emission control
- On Board Diagnostic
- Interface with the immobilization system
- Speed control
The ECM controls the engine fueling by providing sequential fuel injection to all cylinders. Ignition is controlled by a direct ignition system, provided by eight plug top coils. The ECM is able to detect and correct for ignition knock on each cylinder and adjust the ignition timing for each cylinder to achieve optimum performance.
The ECM uses a torque-based strategy to generate the torque required by the driver and other vehicle control modules. The EMS uses various sensors to determine the torque required from the engine. The EMS also interfaces with other vehicle electronic control modules's, via the CAN bus, to obtain additional information (e.g. road speed from the ABS control module). The EMS processes these signals and decides how much torque to generate. Torque is then generated by using various actuators to supply air, fuel and spark to the engine (electronic throttle, injectors, coils, etc.).
The EMS comprises the following inputs:
- CMP sensor
- CKP sensor
- Fuel rail pressure sensor
- MAF sensor
- Knock sensors
- Fuel rail temperature sensor
- ECT sensor
- Engine oil temperature sensor
- MAP sensor
- Electric throttle feedback sensor
- Secondary Air Injection (SAI) MAP sensor
- APP sensor
- DMTL (NAS only)
- Cooling fan speed feedback.
- Heated Exhaust Gas Oxygen (HEGO) sensors
- Universal Heated Exhaust Gas Oxygen (UHEGO) sensors
- Brake switch
- Speed control cancel/suspend switch
- Automatic speed limiter switch
- Crank request signal
- IAT sensor
- External air temperature sensor
The EMS comprises the following outputs:
- Fuel injectors
- Ignition coils
- Engine cooling fan
- Electric throttle
- Electric fuel pump driver module
- VCT solenoids
- Purge valve
- EGR valve
- Secondary air injection pump
- Starter relay control
IGNITION MODES
The vehicle has a possible 4 ignition modes. The modes and systems that are active in each mode are detailed in the following table.
COMPONENTS
Engine Control Module (ECM)
The ECM is located in the plenum area on the passenger side of the engine compartment attached to the bulkhead.
The ECM has the following inputs:
- RCM
- Park/neutral switch
- Ignition coil feedback x2
- Fuel rail temperature
- Mass air flow
- Engine speed
- Camshaft position x2
- Driver demand
- Brake pedal position switch
- Speed control switches
- Generator load
- Oxygen sensors pre catalyst x2
- Oxygen sensors post catalyst x2
- Throttle position
- Cooling fan speed
- Ignition switch position
- Knock sensors x2
- MAP
- Coolant temperature
- Engine oil temperature
The ECM outputs to the following:
- Brake vacuum pump relay
- Ignition coils (x8)
- Oxygen sensor heaters (4)
- Fuel injectors (8)
- Purge Valve
- Engine Cooling Fan
- Fuel pump relay
- Starter Relay
- EMS Main Relay
- Viscous Fan Control
- Generator Control
- Diagnostic Monitoring of Tank Leakage (DMTL) (NAS Only)
- E box fan
Crankshaft Position Sensor (CKP)
The crankshaft position sensor is mounted at the rear underside of the engine near the transmission bell housing. Connection between the sensor and the harness is via a link harness and a two-way connector. Both wires go directly to the ECM. The sensor produces the signal which enables the ECM to determine the angle of the crankshaft, and the engine rpm. From this, the point of ignition, fuel injection, etc. is calculated. If the signal wires are reversed a 3 degrees advance in timing will occur, as the electronics within the ECM uses the falling edge of the signal waveform as its reference / timing point for each tooth.
The reluctor is pressed into the flywheel and has a "tooth" pattern based on 36 teeth at 10 degrees intervals and approximately 5 degrees wide: one of the teeth is removed to provide a hardware reference mark which is 30 degrees BTDC (before top dead center) No.1 cylinder. Because of the crankshaft sensor's orientation, the target wheel uses windows stamped into the face, rather than actual teeth.
The sensor operates by generating an output voltage caused by the change in magnetic field that occurs as the windows pass in front of the sensor. The output voltage varies with the speed of the windows passing the sensor, the higher the engine speed, the higher the output voltage. Note that the output is also dependent on the air gap between the sensor and the teeth (the larger the gap, the weaker the signal, the lower the output voltage). The ECM transmits the engine speed to other vehicle control modules on CAN.
Camshaft Position Sensor (CMP)
Two sensors are located at the rear of the engine, in the cylinder head (one per bank), above the rear cylinders. The sensors are Variable Reluctor Sensor (VRS) type, producing four pulses for every two engine revolutions. The sensing element is positioned between 0 and 2mm from the side of the cam gear wheel.
The camshaft timing wheel is a sintered component which has four teeth on it to enable the EMS to detect cylinder identification. The signal is used for:
- Cylinder recognition
- Enabling sequential fuel injection
- Knock control
- Cylinder identification for diagnostic purposes.
Failure symptoms include:
- Ignition timing reverting to the base mapping, with no cylinder correction.
- Active knock control is disabled, along with its diagnostic (Safe ignition map - loss of performance).
- Quick cam/crank synchronisation on start disabled.
Engine Coolant Temperature Sensor (ECT)
The sensor is located at the front of the engine in the water pipe below the throttle body. The ECT (engine coolant temperature) sensor is a thermistor used to monitor the engine coolant temperature. The engine coolant temperature sensor is vital to the correct running of the engine as a richer mixture is required at lower block temperatures for good quality starts and smooth running, leaning off as the temperature rises to maintain emissions and performance.
The sensor has an operating temperature range of -30 Degrees Celsius to 125 Degrees Celsius. When a defective coolant sensor is detected, the ECM defaults to the oil temperature sensor value.
Engine Oil Temperature Sensor
Oil temperature is monitored through a temperature sensor mounted in the oil system. This component is a NTC (negative temperature coefficient) type. The sensor is mounted next to the oil pressure sensor at the front of the engine and locates into the oil filter bracket.
Oil Pressure Sensor
The oil pressure sensor is located in the oil filter bracket adjacent to the oil temperature sensor. The sensor is hardwired to the instrument cluster and is used to illuminate the oil pressure warning indicator. The sensor switches on at pressures below 24.5kPa and is closed circuit at zero oil pressure.
Fuel Rail Temperature Sensor
The fuel rail temperature sensor measures the temperature of the fuel in the fuel rail. This input is then used to deliver the correct quantity of fuel to the engine. Operating Range -40 Degrees Celsius to 150 Degrees Celsius. The fuel rail temperature sensor is fitted on the rear of the right hand bank (bank A) fuel rail.
Diagnostic Monitoring of Tank Leakage (DMTL) - NAS ONLY
Charcoal Canister with DMTL Pump (NAS only)
The DMTL system periodically checks the evaporative system and the fuel tank for leaks when the ignition is switched off. The DMTL pump is connected to the atmospheric vent of the charcoal cannister and incorporates a PTC heating element a normally open valve and a reference orifice. The DMTL pump is only operated when the ignition is switched off and is controlled by the ECM. The ECM also monitors the electric air pump operation and the normally open valve for faults. To check the fuel tank and EVAP system for leaks the ECM operates the DMTL pump and monitors the current draw. This is compared to a referenced figure established from the current draw when air is pumped through the reference orifice.
Purge Valve
Purge Valve and Hoses location
The purge valve is located LH side of the engine, on a bracket which is attached to the cylinder block. The purge hose is routed from the purge valve, along the left hand side of the air intake manifold, to the elbow assembly which locates the electric throttle.
The purge hose is connected, at the right hand rear of the engine, with a quick release coupling to the purge line which runs parallel with the fuel feed line and around the rear of the fuel tank to the charcoal canister.
The purge hose continues from the purge valve and is routed to a connection on the air intake elbow assembly. The hose is connected to the elbow with a quick release connector.
The purge valve is a solenoid operated valve which is closed when de-energized. The purge valve is controlled by a 10Hz PWM signal from the ECM. When the engine operating conditions are correct, the ECM opens the purge valve which causes fuel vapor and fresh air to be drawn through the charcoal cannister. The fresh air is drawn through the charcoal cannister via the DMTL pump fresh air vent.
Mass Air Flow/Intake Air Temperature Sensor (MAF/IAT)
The air flow meter is located in the clean air duct immediately after the air filter box.
The air mass flow is determined by the cooling effect of inlet air passing over a hot film element contained within the device. The higher the air flow the greater the cooling effect and the lower the electrical resistance of the hot film element. The ECM then uses this signal from the MAF meter to calculate the air mass flowing into the engine.
The measured air mass flow is used in determining the fuel quantity to be injected in order to calculate the required air/fuel mixture required for correct operation of the engine and exhaust catalysts. Should the device fail there is a software backup strategy that will be evoked once a fault has been diagnosed.
The following symptoms may be observed if the sensor fails:
- During driving the engine RPM might dip, before recovering.
- Difficulty in starting or start - stall.
- Poor throttle response / engine performance.
- Lambda control and idle speed control halted.
- Emissions incorrect.
- AFM signal offset
The IAT sensor is integrated into the MAF meter. It is a temperature dependent resistor (thermistor), i.e. the resistance of the sensor varies with temperature. This thermistor is a NTC type element meaning that the sensor resistance decreases as the sensor temperature increases. The sensor forms part of a voltage divider chain with an additional resistor in the ECM. The voltage from this sensor changes as the sensor resistance changes, thus relating the air temperature to the voltage measured by the ECM.
The ECM stores a 25 Degrees C default value for air temperature in the event of a sensor failure.
Manifold Absolute Pressure Sensor (MAP)
The MAP sensor provides a voltage proportional to the absolute pressure in the intake manifold. This signal allows the load on the engine to be calculated and used within the internal calculations of the ECM. The sensor is located on the rear of the air intake manifold.
The output signal from the MAP sensor, together with the CKP and IAT sensors, is used by the ECM to calculate the amount of air induced into the cylinders. This enables the ECM to determine ignition timing and fuel injection duration values.
The MAP sensor receives a 5V supply voltage from ECM and provides an analogue signal to the ECM, which relates to the absolute manifold pressure and allows the ECM to calculate engine load. The ECM provides a ground for the sensor.
If the MAP signal is missing, the ECM will substitute a default manifold pressure reading based on crankshaft speed and throttle angle. The engine will continue to run with reduced drivability and increased emissions, although this may not be immediately apparent to the driver. The ECM will store fault codes which can be retrieved using the Integrated Diagnostic System (IDS).
Knock Sensors
The V8 EMS has two knock sensors located in the V of the engine, one per cylinder bank. The sensors are connected to the ECM via a twisted pair.
The knock sensors produce a voltage signal in proportion to the amount of mechanical vibration generated at each ignition point. Each sensor monitors the related cylinder bank.
Care must be taken at all times to avoid damaging the knock sensors, but particularly during removal and fitting procedures. The recommendations regarding torque and surface preparation must be adhered to. The torque applied to the sensor and the quality of the surface preparation both have an influence over the transfer of mechanical noise from the cylinder block to the crystal.
The knock sensors incorporate a piezo-ceramic crystal. This crystal produces a voltage whenever an outside force tries to deflect it, (i.e. exerts a mechanical load on it). When the engine is running, the compression waves in the material of the cylinder block, caused by the combustion of the fuel/air mixture within the cylinders, deflect the crystal and produce an output voltage signal. The ECM uses the signals supplied by the knock sensors, in conjunction with the signal it receives from the camshaft sensor, to determine the optimum ignition point for each cylinder. The ignition point is set according to preprogrammed ignition maps stored within the ECM. The ECM is programmed to use ignition maps for 98 RON premium specification fuel. It will also function on 91 RON regular specification fuel and learn new adaptions. If the only fuel available is of poor quality, or the customer switches to a lower grade of fuel after using a high grade for a period of time, the engine may suffer slight pre-ignition for a short period. This amount of pre-ignition will not damage the engine. This situation will be evident while the ECM learns and then modifies its internal mapping to compensate for the variation in fuel quality. This feature is called adaption. The ECM has the capability of adapting its fuel and ignition control outputs in response to several sensor inputs.
The ECM will cancel closed loop control of the ignition system if the signal received from either knock sensor becomes implausible. In these circumstances the ECM will default to a safe ignition map. This measure ensures the engine will not become damaged if low quality fuel is used. The MIL will not illuminate, although the driver may notice that the engine 'pinks' in some driving conditions and displays a drop in performance and smoothness.
When a knock sensor fault is stored, the ECM will also store details of the engine speed, engine load and the coolant temperature.
Electric Throttle
The V8 EMS incorporates an electric throttle control system. The electronic throttle body is located on the air intake manifold in the engine compartment. The system comprises three main components:
- Electronic throttle control valve
- APP sensor
- ECM
When the accelerator pedal is depressed the APP sensor provides a change in the monitored signals. The ECM compares this against an electronic map and moves the electronic throttle valve via a PWM control signal which is in proportion to the APP angle signal. The system is required to:
- Regulate the calculated intake air load based on the accelerator pedal sensor input signals and programmed mapping.
- Monitor the drivers input request for cruise control operation.
- Automatically position the electronic throttle for accurate speed control.
- Perform all dynamic stability control throttle control interventions.
- Monitor and carry out maximum engine and road speed cut out.
- Provide differing responses for differing Terrain response modes.
A software strategy within the ECM enables the throttle position to be calibrated each ignition cycle. When the ignition is turned ON, the ECM performs a self test and calibration routine on the electronic throttle by closing the throttle full, then opening again. This tests the default position springs.
Accelerator Pedal Position Sensor (APP)
The APP sensors are located on the accelerator pedal assembly.
The APP sensors are used to determine the driver's request for vehicle speed, acceleration and deceleration. This value is used by the ECM and the throttle is opened to the correct angle by an electric motor integrated into the throttle body.
The APP sensor signals are checked for range and plausibility. Two separate reference voltages are supplied to the pedal. Should one sensor fail, the other is used as a 'limp home' input. In limp home mode due to an APP signal failure the ECM will limit the maximum engine speed to 2000 rpm.
Stoplamp Switch
The stoplamp switch is mounted on the brake pedal bracket and is connected to the vehicle harness via a 4 pin multiplug.
When the brake pedal is pressed, the switch contacts close allowing a hard wired signal feed to be sent to the ECM. A stoplamp switch status message is then sent from the ECM to the ABS module on the high speed CAN bus.
Oxygen Sensors
There are four oxygen sensors located in the exhaust system. Two upstream before the catalytic converter and two down stream after the catalytic converter. The sensor monitors the level of oxygen in the exhaust gases and is used to control the fuel/air mixture. Positioning a sensor in the stream of exhaust gasses from each bank enables the ECM to control the fueling on each bank independently of the other, allowing much closer control of the air / fuel ratio and catalyst conversion efficiency.