323000503 - INTRODUCTION - DIESEL FUEL INJECTION SYSTEM

SPECIFICATIONS

Function

The Magneti Marelli MJD 6F3 Common Rail system is a high pressure electronic injection circuit for fast, direct injection diesel engines.Its main features are:- availability of high injection pressure (up to 1600 bar)- possibility of modulating pressures between 150 bar up to a maximum service pressure of 1600 bar, regardless of engine speed and load;- ability to work at high engine rpms (up to 5000 rpm in full load conditions);- injection control precision (injection advance and duration);- reduction in fuel consumption;- reduction in emissions.The main system functions are as follows:- engine coolant temperature control;- control of amount of fuel injected;- idle speed check;- fuel cut-off during over-run;- cylinder balance check when idling;- control of anti-judder function- exhaust fumes control during acceleration;- exhaust gas recirculation control (E.G.R.);- maximum torque limit control;- maximum speed limit control;- control of heater plugs;- control of climate control system activation (where fitted);- auxiliary fuel pump check;- cylinder position check for timing;- main and multiple injection advance check;- injection pressure closed cycle check;- electrical balance check;- IMA injector calibration;- fuel pressure control;- Lambda sensor control;- control of variable geometry compressor;- engine oil life check.1. Fuel tank2. Auxiliary fuel pump3. Fuel filter4. Fuel return manifold5. Pressure pump6. Pressure regulator on pump7. Rail8. Fuel pressure sensor on rail9. Injectors10. Air filter11. Air flow meter12. Compressor13. Intercooler14. E.G.R. solenoid15. Water/exhaust gas heat exchanger for E.G.R. system.16. E.G.R. diffuser17. Pressure relief and air temperature sensor18. Rpm sensor19. Timing sensor20. Water temperature sensor21. Minimum engine oil pressure switch22. Heater plugs23. Heater plugs control unit24. Variable geometry turbocharger (VGT)25. VGT actuator26. VGT actuator solenoid valve27. Lambda sensor (UEGO)28. Catalytic converter29. Pedal assembly30. Injection control unit

OPERATION

Operating strategies

IntroductionThe Common Rail system makes it possible to carry out two pilot injections before T.D.C. with the advantage of distributing the pressure in the combustion chamber more evenly and reducing the combustion noise typical of direct injection engines and up to two injections after the main injection with the advantage of reducing emissions.The control unit controls the quantity of fuel injected, regulating the line pressure and injection times.The control unit processes the following information in order to control the quantity of fuel to inject:- engine rpm;- coolant temperature;- supercharging pressure;- air temperature (from flow meter);- intake air quantity;- battery voltage;- diesel pressure;- accelerator pedal position;- diesel temperature;- Lambda signals.Diagram showing information entering/leaving the control unit1. Auxiliary electric fuel pump2. Lambda sensor3. VGT solenoid4. Air conditioning compressor (where fitted)5. E.G.R. solenoid6. Rev counter7. Cooling fan8. Heater plugs control unit9. Twin track accelerator pedal potentiometer10. Brake pedal switch11. Clutch pedal switch12. Fuel temperature sensor13. Fuel pressure sensor14. Air flow meter15. Coolant temperature sensor16. Water in diesel filter sensor17. Cruise control (where fitted)18. Pressure relief and air temperature sensor19. Timing sensor20. Engine rpm sensor21. Speedometer22. Battery23. Fiat CODE (body computer)24. Diagnostic socket25. Injectors26. Heater plugs27. Pressure regulator on pump28. Heater plugs warning light29. Injection warning light30. Coolant overheating warning light31. Water in the fuel filter warning light32. OIL warning lightSelf-diagnosisThe control unit self-diagnostic system checks the signals coming from the sensors and compares them with the permitted limits.SIGNALLING OF FAULTS DURING STARTING:- Warning light on until engine is started indicates test stage;- Warning light off after engine starting indicates no fault with components that affect the safety of the system;- Warning light on with engine running indicates fault.FAULT SIGNALS DISPLAYED DURING OPERATION:- Warning light on indicates fault;- Warning light off indicates no fault with components that affect the safety of the system;RECOVERYThe control unit defines the recovery settings on each specific occasion according to which components are faulty.The recovery parameters are managed by components that are not faulty.Fiat Code recognitionThe moment the control unit receives the ignition ON signal it converses with the body computer via the CODE function to obtain the go ahead for starting.Fuel temperature controlWith the temperature of the fuel at 80 °C measured by the sensor in the diesel filter, the control unit operates the pressure regulator to reduce the line pressure and, if this is not enough, to also reduce the amount of fuel injected.Engine coolant temperature controlWhen the engine coolant temperature is above 105°C, the control unit:- reduces injected fuel quantity (reduces engine power);- controls the cooling fan- switches on the coolant temperature warning light.Control of the amount of fuel injectedThe control unit compares the signals coming from the sensors to the stored values, and:- controls the regulator on the pressure pump to modulate the fuel flow rate- varies the "pilot" injection time in the entire rpm range;- alters the "main" injection time.Idle speed checkThe control unit processes the signals coming from the sensors and regulates the quantity of fuel injected:- controls the pressure regulator;- alters the injector injection times.Within certain limits the speed is dependent on battery voltage.Fuel cut-off during over-runWhen the accelerator pedal is released, the control unit implements the following strategies:- places the injector opening time at zero;- partly varies the injection time for the injectors before the idle speed is reached;- controls the fuel pressure regulator.Idle cylinder balance checkAccording to the signals received from the sensors, the control unit controls the idle speed torque:- alters the quantity of fuel injected by the individual injectors (injection time).Anti-judder checkThe control unit processes the signals received by the various sensors and corrects the quantity of fuel to inject in order to improve driveability reducing shuddering whilst driving by means of the injector opening time.Exhaust fume control during accelerationIn order to restrict the fumes during fast transitions, on the basis of the signals received from the accelerator pedal potentiometer, Lambda sensor, flow meter and the engine speed the control unit limits the amount of fuel to be injected by means of:- the pressure regulator- the injection time.- E.G.R.Exhaust gas recirculation control (E.G.R.)In accordance with EURO 4 pollution control legislation, on the basis of the engine load and the signal from the accelerator pedal potentiometer, the control unit limits the quantity of intake air, implementing the partial intake of exhaust gases, through:- the adjustment of the opening of the E.G.R. valve.Maximum torque limit controlThe control unit uses mapped values plotted against rpm to calculate the following:- the torque limit;- the permitted fumes (limit).It compares these minimum values with other parameters and corrects them:- coolant temperature;- engine rpm;- vehicle speed;- air temperature.It also controls the quantity of fuel to be injected (pressure regulator - injectors).Maximum speed limit controlWhen the engine speed reaches 5200 rpm, the control unit interrupts the operation of the injectors and the supply pressure is consequently reduced.Glowheater plug checkThe injection control unit, during the following stages:- starting;- post-starting;times the operation of the glowheater plug control unit on the basis of engine temperature.Air conditioning system start of operation checkThe control unit operates the climate control compressor:- switching it on/off when the switch is pressed;- switching it off momentarily (for a few seconds) in the case of strong acceleration or a request for maximum power.Auxiliary fuel pump checkIrrespective of the rpm, the control unit:- supplies the auxiliary fuel pump with the ignition ON;- cuts off the auxiliary pump supply if the engine is not started within a few seconds.Cylinder position checkDuring each revolution of the engine the control unit recognises which cylinder is in the combustion stroke and controls the injection sequence within the appropriate cylinder.Pilot injection and main injection advance checkAccording to the signals coming from the various sensors, including the absolute pressure sensor built into the control unit itself, the control unit determines the optimum injection point, according to an internal map, designed for driving comfort and also designed to meet EURO 4 emission limits.Injection pressure closed loop checkThe control unit controls the regulator on the pressure pump to produce optimum line pressure according to engine load, which is determined by processing signals from the various sensors.Electrical balance checkThe control unit modulates idle speed according to the battery voltage and:- increases the injector injection times;- modulates the line pressure.Fan controlDepending on the temperature of the coolant and the pressure of the refrigerant fluid in the air conditioning system, the control unit controls:- fan activation at first or second or third speedCruise control system check (where fitted)Depending on the position of the control lever, the control unit directly controls the quantity of fuel injected to control and maintain the vehicle speed memorized.A warning light on the dashboard, activated by the control unit, indicates system operation or deactivation status.The cruise control is temporarily disabled:- by operating the brake;- by operating the clutch;- the resume button returns the stored speed.The cruise control is not disabled when the accelerator is pressed (e.g. to overtake) and automatically restores the vehicle to the set speed as soon as the accelerator is released.The ASR function (antispin) takes precedence over cruise control for safety reasons.