Part 1
Electronic Engine Controls
Electronic Engine Controls:
Electronic Engine Controls:
OVERVIEW
The V8 supercharged engine is controlled by an ECM. The Engine Management System (EMS) controls the following:
- Engine fueling
- Ignition timing
- Closed loop fueling
- Knock control
- Idle speed control
- Emission control
- On Board Diagnostic (OBD)
- 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.).
ENGINE CONTROL MODULE (ECM)
Engine Control Module (ECM):
The ECM and bracket assembly are attached to the vehicle on the left hand side in the secondary bulkhead area using 3 m6 nuts, 2 off onto the longitudinal and 1 off to the wheel arch apron panel.
System ECM has the following inputs:
- RCM
- Park/neutral switch
- Ignition coil feedback x8
- Fuel rail temperature
- Fuel rail pressure
- Supercharger inlet pressure
- 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
- Manifold Absolute pressure (MAP)
- Intercooler temperature
- Coolant temperature
- Engine oil temperature
The ECM outputs to the following:
- Electric throttle Actuator
- 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
- Electric Fan Control
- Generator Control
- Fuel tank leakage monitoring (NAS Only)
- Fuel Pump Driver Module (FPDM)
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° intervals and approximately 5° wide: one of the teeth is removed to provide a hardware reference mark which is 30 degrees BTDC 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 crankshaft 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 OIL TEMPERATURE SENSOR
Oil temperature is monitored through a temperature sensor mounted in the oil system. This component is a NTC. The sensor is mounted next to the oil pressure sensor at the front of the engine and locates into the oil filter bracket.
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. The sensors operating range is -40 Degrees Celsius to 150 Degrees Celsius. The fuel rail temperature sensor is fitted on the rear of the right hand bank fuel rail.
FUEL RAIL PRESSURE SENSOR
The fuel rail pressure sensor is located on top of the fuel rail adjacent to the fuel inlet. The fuel rail pressure sensor measures the pressure of the fuel in the fuel rail. This input is then used by the fuel pump control module to control the amount of fuel delivered to the fuel rail.
FUEL TANK LEAKAGE MONITORING - NAS ONLY
Charcoal Canister with fuel tank leakage monitoring Pump (NAS only)
The fuel tank leakage monitoring system periodically checks the evaporative system and the fuel tank for leaks when the ignition is switched off. The fuel tank leakage monitoring 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 fuel tank leakage monitoring 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 fuel tank leakage monitoring 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 on the LH side of the engine on a bracket which is attached to the cylinder head. 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 fuel tank leakage monitoring pump fresh air vent.
MASS AIR FLOW/INLET AIR TEMPERATURE SENSOR (MAF/IAT)
Two MAF/IAT sensors are located in the clean air duct immediately after the air cleaner 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 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 maintain the stoichiometric 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 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 Celsius default value for air temperature in the event of a sensor failure.
MANIFOLD ABSOLUTE PRESSURE SENSOR (MAP)- SUPERCHARGER INLET PRESSURE
The MAP sensor is located in the LH side of the throttle elbow.
The MAP sensor provides a voltage proportional to the absolute pressure in the supercharger intake. This signal allows the load on the engine to be calculated and used within the internal calculations of the MAP. The sensor is located below the electric throttle on the induction elbow.
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.
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 Land Rover recommended diagnostic tool.
MANIFOLD ABSOLUTE PRESSURE AND TEMPERATURE SENSOR (MAPT)
The MAPT is located to the front of the RH engine bank intercooler and is secured with a single bolt. The sensor measures the pressure and temperature of the inducted air prior to it entering the cylinders.
The sensor fits and seals using a radial 'O' ring seal directly to the inlet manifold.
The MAPT signal is used to retard the ignition timing relative to boost pressure. The intercooler temperature is used for air charge density calculations and for intercooler diagnostic purposes.
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.
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 signals are supplied to the ECM, which compares them with `mapped' signals stored in memory. From this, the ECM can determine when detonation occurs on individual cylinders. When detonation is detected, the ECM retards the ignition timing on that cylinder for a number of engine cycles, then gradually returns it to the original setting.
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 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.
ELECTRONIC 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
- 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 EAPP 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 cruise 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.