The Cummins ISF engine control module has a connector consisting of two blocks.
Block “A” is connected to the vehicle wiring. Its composition can vary widely depending on the vehicle equipment.
Through this block the control module receives, among other things, power and is connected to the vehicle ground.
Block “B” combines the engine wiring: sensors and actuators. Its composition depends on the emission standards to which the engine in question corresponds.
Crankshaft position sensor
The crankshaft position sensor is installed in the area of the crankshaft pulley.
The operating principle of the crankshaft position sensor is based on the Hall effect.
The sensor determines the crankshaft position and converts these data into signals (rectangular pulses). Based on these signals, the electronic engine control module determines the crankshaft rotational speed and corrects the injector opening start moment, as well as the duration of its open state and the fuel injection advance angle.
The sensor has three wires: power, ground and signal. The sensor power supply is stabilised, is approximately 5 V and is provided by the engine control module (contact B13). The ground contact is also connected to the control module (contact B14). The sensor signal arrives at contact B38 of the control module and consists of rectangular pulses with a low level of approximately 0 V and a high level of approximately 5 V.
The main sensor faults lie in three areas:
Fault of the sensor itself
The fault of Hall effect sensors manifests itself mainly after the engine has warmed up: the electronics built into the sensor fail from heating. Pulse dropouts occur.
Wiring fault
Manifests itself as a complete or partial absence of the sensor signal. It is diagnosed by checking the voltage at the sensor contacts with the ignition on and the connectors fitted, as well as by checking the continuity of the wiring from the sensor to the control module with the connectors removed.
Fault of the sensor rotor (trigger wheel)
It should be noted that repair of the rotor teeth in the event of damage is not permissible: the rotor must be replaced. Welding changes the magnetic properties of the material and sensor signal faults are likely when passing a repaired tooth.
The absence of tachometer needle movement during unsuccessful engine start attempts can serve as an indicator of a possible crankshaft position sensor fault.
Camshaft position sensor
The camshaft position sensor is located on the cylinder head and determines the moment when the No. 1 cylinder piston reaches top dead centre on the compression stroke. Based on the sensor signal, the electronic engine control module determines the fuel injection order for the individual cylinders.
The operating principle of the camshaft position sensor is based on the Hall effect.
The sensor has three wires: power, ground and signal. The sensor power supply is stabilised, is approximately 5 V and is provided by the engine control module (contact B87). The ground contact is also connected to the control module (contact B63). The sensor signal arrives at contact B62 of the control module and consists of rectangular pulses with a low level of approximately 0 V and a high level of approximately 5 V.
The main sensor faults lie in three areas:
- Fault of the sensor itself. The fault of Hall effect sensors manifests itself mainly after the engine has warmed up: the electronics built into the sensor fail from heating. Pulse dropouts occur.
- Wiring fault, including the connectors. Manifests itself as a complete or partial absence of the sensor signal. It is diagnosed by checking the voltage at the sensor contacts with the ignition on and the connectors fitted, as well as by checking the continuity of the wiring from the sensor to the control module with the connectors removed.
- Fault of the sensor rotor (trigger wheel).
Boost pressure sensor and air temperature sensor as an assembly
The boost pressure sensor is installed on the intake manifold and is a piezoresistive type sensor. The sensor determines the boost pressure created by the turbocharger directly in the intake manifold, producing an output signal to the control module.
A charge-air temperature sensor is built into the boost pressure sensor.
The sensor has four wires: power, ground, boost pressure sensor signal wire and charge-air temperature sensor signal wire.
The sensor power supply is stabilised, is approximately 5 V and is provided by the engine control module (contact B89). The ground contact is also connected to the control module (contact B65).
The boost pressure sensor signal arrives at contact B70 of the control module and represents a voltage that increases with pressure. The charge-air temperature sensor signal arrives at contact B23 of the control module.
Fuel rail pressure sensor
The fuel pressure sensor is installed on the fuel accumulator (fuel rail) and measures the instantaneous fuel pressure values in the accumulator with adequate accuracy and speed.
The fuel enters the sensor through a hole in the accumulator and a channel in the sensor body, closed at the end by a diaphragm; thus the fuel under pressure acts on the diaphragm. The sensor sensing element, in turn, converts the pressure into an electrical signal. This signal is sent to the electronic engine control module.
Based on the fuel pressure sensor signal and depending on the signals of other fuel system components, the electronic engine control module makes the necessary corrections to the fuel system operation (the required fuel pressure in the accumulator is created by controlling the high-pressure pump actuator).
The sensor has three wires: power, ground and signal. The sensor power supply is stabilised, is approximately 5 V and is provided by the engine control module (contact B92). The ground contact is also connected to the control module (contact B68). The sensor signal arrives at contact B69 of the control module and represents a voltage that increases with pressure.
Coolant temperature sensor
The coolant temperature sensor is installed in the thermostat housing. It determines the engine coolant temperature and transmits the signal to the electronic engine control module.
The sensor is a thermistor. The sensor resistance decreases as the coolant temperature increases. The electronic engine control module evaluates the coolant temperature from the sensor signal voltage and makes the necessary corrections to the fuel system operation.
The sensor has two wires: ground (contact B43 of the control module) and a signal wire which is at the same time the power wire (contact B46 of the control module). With the ignition on, a stabilised supply of approximately 5 V must be present at contact 2 of the disconnected sensor connector.
Accelerator pedal position sensor
The accelerator pedal position sensor is necessary to determine the degree to which the driver presses the accelerator pedal.
The sensor consists of two potentiometers (variable resistors) having independent circuits (power, signal and “ground”). Thus the sensor consists of two channels — 1 and 2. When the accelerator pedal is pressed, the resistances of the sensor resistors change smoothly in proportion to the degree of pedal depression.
The accelerator pedal position sensor signals arriving at the electronic engine control module are compared with the programmed characteristic curves (the signals from channels 1 and 2 are also compared with each other, which is necessary to check the correctness of the readings). The control module, in turn, generates output control signals on the basis of which the fuel system operation is controlled (for example, it determines the required fuel delivery).
Oil pressure emergency sensor
The oil pressure emergency sensor is a relay (switching) sensor whose contacts close when the oil pressure in the engine lubrication system falls below a certain level.
The sensor signal arrives at the control module at contact 37B: the sensor closes this circuit to ground. Receipt of the signal from this sensor with the engine running (the crankshaft position sensor signal is received) causes the engine control module to command the “STOP” fault indicator on the instrument panel to come on.
Depending on the implementation of the data exchange system between the instrument cluster and the engine control module, this command can be transmitted either via a separate circuit (contact A49) or via the CAN data bus (contacts 14A and 15A).
Atmospheric pressure sensor
The atmospheric pressure sensor determines the current atmospheric pressure and transmits the signal to the engine control module. This sensor is necessary for correct engine operation at different altitudes above sea level.
The sensor has three wires: power, ground and signal. The sensor power supply is stabilised, is approximately 5 V and is provided by the engine control module (contact B88). The ground contact is also connected to the control module (contact B64). The sensor signal arrives at contact B72 of the control module and represents a voltage that changes with pressure.
Actuators
High-pressure fuel pump (injection pump)
An electromagnetic fuel pressure regulator is mounted on the high-pressure pump. It maintains the working fuel pressure in the accumulator depending on the engine load. When it is necessary to increase the fuel pressure in the accumulator, the electromagnetic regulator valve closes on a signal from the electronic engine control module, isolating the high-pressure stage from the low-pressure line (fuel return). When it is necessary to reduce the fuel pressure in the accumulator, the electromagnetic regulator valve, on the contrary, opens on a signal from the electronic engine control module, bypassing part of the fuel to the return line and thereby reducing the fuel pressure in the accumulator.
Injectors
The injectors inject fuel into the engine cylinders on a signal from the electronic engine control module. In the Common Rail accumulator fuel system, solenoid-driven injectors are installed.
Turbocharger variable geometry actuator
Some engine modifications are fitted with a variable geometry turbocharger. The variable geometry system actuator is installed on the turbocharger and controls the turbocharger variable geometry (vane position) system.
The electronic engine control module, receiving data from the crankshaft position sensor, coolant temperature sensor, charge-air temperature sensor, boost pressure sensor and atmospheric pressure sensor, which determine the engine load and its operating conditions, calculates the optimum vane position and sends a signal to the actuator electric motor. Thus the performance of the turbocharger compressor stage is regulated.
CAN data bus
The CAN (Controller Area Network) data bus is a serial high-speed data transmission line developed by Bosch. It has high noise immunity and error protection. It is used to reduce the number of wires in vehicle data exchange. Each of the control modules operating on this bus transmits and receives data selectively.
The bus is implemented according to a two-wire scheme: CAN-High (H) and CAN-Low (L) channels. The wires are twisted into a twisted pair to improve the bus noise immunity. The maximum length of untwisted wires must not exceed 40 mm to ensure the necessary potential difference between the H and L channels, as well as to prevent the appearance of errors in messages, possible with signal reflections.
Inside the modules, at the ends of the bus, resistors, usually rated 120 ohms, are built in parallel to the CAN bus terminals. These resistors also help to determine the serviceability of the bus wiring in its various branches: by measuring the resistance at the corresponding contacts of the removed connectors of the control modules operating on the CAN bus, one should usually obtain approximately 120 or 60 ohms (one 120 ohm resistor or their parallel connection). Depending on which module connector is removed (variants are possible). Depending on the system implementation, these resistors may be installed inside the control modules, inside intermediate CAN bus connectors or inside special CAN bus terminators.
Example of building a CAN data bus in a vehicle (various variants are possible).
The information bus load depends on the number of modules on it and on the amount of information transmitted. The signals on both channels are always symmetrical to each other and in antiphase.
At rest, on both bus channels (High and Low) approximately 2.5 V should be observed (corresponding to logic “1”). The CAN-Low (L) channel signal switches between its high level of 2.5 V (logic “1”) and low level of 1.5 V (logic “0”). The CAN-High (H) channel signal switches between its low level of 2.5 V (logic “1”) and high level of 3.5 V (logic “0”). Thus, when the bus switches to logic “0”, the potential difference between the channels is 2 V.
Possible CAN bus faults lie in three areas:
- wiring/connector fault (open circuit, short circuit, short to ground or power supply);
- faults of the control modules operating on the bus;
- superposition of interference on the CAN bus wiring (incorrect wiring routing, wiring not twisted into a twisted pair).
Exhaust emission reduction system
Modern engines must meet increasingly stringent requirements for the toxicity of their exhaust gases. In order for the engine to meet stricter environmental requirements, its design is optimised, the management system and fuel equipment are improved, and additional exhaust emission reduction subsystems are installed. In addition, the appropriate fuel must be used.
The following figure shows an approximate graph of the effect of introducing emission reduction subsystems on the corresponding exhaust parameters: NOx — nitrogen oxides, PM — solid particles, incl. soot.
Exhaust gas recirculation subsystem (EGR)
The exhaust gas recirculation (EGR) subsystem is installed on some engine models to achieve Euro 3 emission standards, and together with fuel supply correction, Euro 4 standards. On engine models complying with Euro 3, it may be absent.
The EGR subsystem reduces emissions of nitrogen oxides (NOx) into the atmosphere. The air contains molecular nitrogen, which under normal conditions is inert and does not react with the oxygen also present in the air. But, entering the engine combustion chamber, under the influence of high temperatures, nitrogen oxidises, resulting in toxic nitrogen oxides. The higher the temperature, the more nitrogen oxides are formed.
The exhaust gas recirculation system directs part of the exhaust gases from the engine exhaust manifold through the intake manifold back into the combustion chambers, thereby reducing the combustion temperature of the air-fuel mixture and consequently the formation of nitrogen oxides.
Composition of the EGR subsystem
There are several versions of the EGR subsystem on Cummins ISF engines, depending on which its composition differs. On ISF3.8 engines the EGR subsystem includes: EGR valve assembly, EGR cooler and electronic control system elements.
The EGR valve has an electric actuator which, on command from the control module, opens and closes the recirculation channel by the required amount. The amount of recirculated gases is determined by the mass air flow sensor: a decrease in air flow lets the control module know that exhaust gases are entering the engine.
The throttle valve servo drive is installed on the intake manifold and is necessary for regulating the throttle valve position. The servo drive consists of a DC electric motor and a throttle valve position sensor. The throttle valve servo drive in the diesel engine intake system serves to increase the EGR rate by reducing the increased pressure in the intake manifold (this is achieved by partially closing the throttle valve), as a result of which exhaust gases are drawn into the intake. Throttle valve regulation is carried out only at low speed modes.
Disadvantages of EGR
During operation, the soot contained in the exhaust gases clogs the recirculation channels and the EGR valve. Thus, sooner or later the valve movement is blocked and it ceases to perform its functions. Usually the valve blocking occurs when it is partially open, so that the recirculated gases are always supplied to the intake tract, even when this should not happen. This leads to a violation of the air-fuel mixture composition and, as a consequence, to a loss of available power and increased exhaust smoke. This problem is not always solved by flushing the valve: it may fail and will need to be replaced.
Solid particles of the exhaust gases also contaminate the intake manifold and intake valves. The contamination can be so severe that the vehicle may simply stop: air ceases to enter the engine. Flushing the intake manifold solves this problem. In addition, due to EGR the engine oil loses its properties faster.
Furthermore, EGR worsens the fuel economy of the diesel engine and leads to a reduction in its thermal efficiency.
As we can see, this subsystem causes certain harm to the engine, which is why many vehicle owners remove its elements: all gas recirculation pipes, the recirculation valve, the gas cooler (the heat exchanger in which the heat of the recirculated exhaust gases is transferred to the engine cooling system) are removed, and blanking plugs are installed in place of all pipes. But this is not enough: if one confines oneself only to the physical removal of the EGR subsystem, the control module that monitors its operation will detect the fault and inform the driver by turning on the indicator on the instrument panel. Therefore, additional reprogramming of the engine control module is required (replacement of the control programme — chip tuning), as a result of which the module will stop monitoring the EGR elements, and the working control maps will be replaced with maps corresponding to Euro 3 standards.
Diesel particulate filter (DPF)
The soot of internal combustion engine exhaust gases, acting like activated carbon, collects harmful substances and is a carcinogen, so inhaling it is extremely undesirable. The diesel particulate filter (DPF) is intended to reduce the amount of soot and other solid particles in the vehicle exhaust gases. Its function is to trap solid particles from the exhaust gases and periodically burn them (DPF regeneration). The total surface area of the filter element is close to that of two football pitches.
As can be seen from the above graph, the DPF works together with the EGR: the EGR reduces nitrogen oxides but increases the amount of solid particles in the exhaust gases, which in turn is solved by the DPF.
Composition of the DPF subsystem
The DPF subsystem consists of the particulate filter and the differential pressure sensor in the particulate filter. In this composition this system is installed, for example, on Next Bus buses.
The differential pressure sensor in the particulate filter is necessary for monitoring the filter filling. Its readings allow the control module to determine the moment when regeneration is required. The DPF regeneration is carried out by heating it to a temperature of approximately 700 °C, as a result of which the solid particles deposited in its channels burn out completely, forming gaseous carbon oxides.
Disadvantages of DPF
Errors in vehicle operation, low fuel quality, unsuitable lubricants, the use of unsuitable fuel and oil additives, frequent short-distance trips and urban driving patterns often lead to irreparable particulate filter faults. Its regeneration becomes impossible.
Faced with this problem, the vehicle owner, as in the case of the catalytic converter, has two ways of solving it: replacement with a new one or removal of the particulate filter. The cost of a new particulate filter is high, and often its removal is the only way to return the vehicle to a working condition. And in this case too, reprogramming of the engine control module will be required, software-disabling the particulate filter.
Selective catalytic reduction catalyst (SCR)
This subsystem is intended to reduce toxic nitrogen oxides NOx (NO, NO2) in the exhaust gases. The presence of this subsystem eliminates the need to use EGR to achieve Euro 4 standards, and its use together with other emission reduction systems allows Euro 5 and Euro 6 standards to be achieved.
As can be seen from the graph, with this subsystem the engine operates in modes optimised for reducing solid particles in the exhaust gases (PM-optimised combustion), and the increase in this case of the NOx content in the exhaust gases is dealt with by the SCR subsystem.
The principle of operation of the SCR system consists in treating the exhaust gases with an aqueous urea solution in a reduction catalytic converter. The nitrogen oxides NOx (NO, NO2) contained in the exhaust gases, after a chemical reaction with the AdBlue reducing agent in the catalyst, are converted into nitrogen N2 and water H2O.
Emission reduction system fluid (urea)
The aqueous urea solution used is known under the brand name AdBlue. The AdBlue reagent is produced using a special technology from high-purity urea and demineralised water. The urea proportion in AdBlue is 32.5 %. At this concentration the reagent has the lowest freezing point, equal to −11 °C. Any deviation from this concentration leads to an increase in the freezing temperature.
Heating of the urea supply system can be carried out both by independent heating elements and from the vehicle cooling system (in this case a tank heating valve is used). The average reagent consumption varies depending on the engine model and should on average be about 4 % of the diesel fuel consumption for engines meeting Euro 4 requirements. The reagent shelf life is 1 year.
Precautions when handling AdBlue
The reagent is not flammable and is classified as safe according to Directive EC67/548/EEC. Ingestion of small amounts of the substance does not present a danger. If AdBlue has entered the digestive organs, rinse the mouth and drink plenty of water. If the feeling of malaise and discomfort do not pass, consult a doctor.
Prolonged contact or immersion of body parts in a tank with the substance may cause skin burns. If contact with the substance is possible, latex gloves should be used. Although the product is not classified as an irritating chemical substance, direct contact with the eyes may cause temporary discomfort characterised by lacrimation or conjunctival redness. In case of direct contact of the solution with the eyes, they should be immediately rinsed with plenty of water and a doctor consulted.
Spills of the reagent should be carefully eliminated in order to prevent injuries, since the spill surface becomes slippery. Contact of the liquid with vehicle parts should be avoided. If this has occurred, the liquid must be washed off with water and residues removed from the body surface. If AdBlue dries and crystallises on the surface, this will cause corrosion.
At high temperatures (approximately 70–80 °C) AdBlue decomposes, which leads to the formation of ammonia and possible unpleasant odour. Contamination by foreign substances and bacteria can make AdBlue unsuitable for use. Spilled and crystallised urea leaves white spots that can be cleaned with water and a brush (if possible immediately). AdBlue has a high penetration ability, so electrical components and connectors should be protected from AdBlue ingress.
Use only AdBlue conforming to the manufacturer’s permitted standard in the original packaging. To exclude contamination, it is forbidden to reuse AdBlue drained from the system. The use in the neutralisation system of water, aqueous solution of ordinary urea and other liquids other than the AdBlue reagent is not permitted, as this may lead to failure of the neutralisation system. When handling AdBlue, observe the established rules.
Practice shows that it is precisely the various contaminations of the liquid itself that are the most common cause of SCR system failures. The liquid is very sensitive to the materials it contacts, primarily metals: zinc, aluminium, copper, cast iron and brass. On contact with these metals, salts are formed which, when entering the catalyst, can put it out of operation.
Catalyst
After the urea is supplied to the catalyst, in the hydrolysis section the urea decomposes into ammonia NH3 and carbon dioxide CO2. In the reduction catalyst, ammonia NH3 reacts with nitrogen oxides NOx, forming molecular nitrogen N2 and water H2O.
For normal catalyst operation it is necessary that it be heated to a temperature of at least 200 °C. To monitor the catalyst temperature and the exhaust gas temperature, exhaust gas temperature sensors are used at the inlet and outlet of the catalytic converter. To monitor the catalyst efficiency, a nitrogen oxide concentration sensor is used at the outlet of the catalytic converter.
Urea injection system
The supply of urea to the exhaust system is carried out by the reagent (urea) dosing module, which comprises a pump, dosing and filtration elements. To distribute the urea uniformly in the exhaust gas flow, a mixer is used. A level sensor with an integrated temperature sensor is installed in the urea tank.
Caution! Operating the vehicle without AdBlue reagent leads to a violation of the operating temperature regime and failure of the neutralisation system.
Urea injection begins when the catalyst reaches its operating temperature, provided that at low ambient temperature a sufficient amount of liquid urea is ensured. Urea injection is interrupted at a small exhaust gas flow volume (idle) and at too low an exhaust gas temperature.
Disadvantages of SCR
The presence of this system on the vehicle obliges the driver to maintain the urea level in the tank, since operating the vehicle with an empty tank is prohibited, and the sales infrastructure is still poorly developed. Certain requirements are also imposed on the quality of the fuels and lubricants used.
Configurable functions
The equipping of the engine management system with additional functions depends on the vehicle equipment. These functions are programmed with diagnostic equipment. Some additional functions are described below:
- Cruise control system. This function can be activated even on vehicles not initially equipped with it. For this, the corresponding control buttons of this system are installed and the control module programme is changed.
- Speed limitation. This function can be programmed at the factory on vehicles intended for transporting children. Deactivation of this function, if the vehicle purpose has changed, is also possible by replacing the control programme.
- Increasing the engine crankshaft speed at idle. This function can be activated on vehicles equipped with the cruise control system. For this, the control module programme is changed, after which the engine speed setting on a stationary vehicle is carried out with the cruise control buttons (engine brake, if equipped).
- Functions required for the power take-off system operation: engine control at constant speed, remote accelerator.
- Some protective functions required for the operation of the engine and other systems: maximum engine speed limitation, battery charging monitoring, immobiliser, service intervals, torque limitation (transmission protection), downshifting.
