199002571 - 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 pressures (1400 bar) for the 75 CV version;- availability of high injection pressures (1600 bar) for the 90 CV version;- possibility of modulating these pressures between 150 bar and the maximum operating value of 1400 bar for the 75 CV version and 1600 bar for the 90 CV version irrespective of the rotation speed and the engine 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.Main system functions are essentially 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 (90 CV version);- engine oil life check.75 CV version1. Fuel tank2. Auxiliary fuel pump3. Fuel filter4. Pressure pump5. Rail6. Pressure regulator7. Fuel pressure sensor8. Injectors9. Air filter10. Air flow meter11. Compressor12. Intercooler13. E.G.R. solenoid valve14. Water/exhaust gas heat exchanger for E.G.R. system.15. E.G.R. diffuser16. Excess pressure sensor17. Rpm sensor18. Timing sensor19. Water temperature sensor20. Minimum engine oil pressure switch21. Heater plugs22. Heater plugs control unit23. Turbocharger24. Waste gate actuator25. Catalytic converter26. Lambda sensor (UEGO)27. Pedal assembly28. Injection control unit90 CV version1. Fuel tank2. Auxiliary fuel pump3. Fuel filter4. Fuel return manifold5. Pressure pump6. Pressure regulator on pump7. Pressure regulator on rail8. Rail9. Fuel pressure sensor on rail10. Injectors11. Air filter12. Air flow meter13. Compressor14. Intercooler15. E.G.R. solenoid valve16. Water/exhaust gas heat exchanger for E.G.R. system.17. E.G.R. diffuser18. Pressure relief and air temperature sensor19. Rpm sensor20. Timing sensor21. Water temperature sensor22. Minimum engine oil pressure switch23. Heater plugs24. Heater plugs control unit25. Variable geometry turbocharger (VGT)26. VGT actuator27. VGT actuator solenoid valve28. Lambda sensor (UEGO)29. Catalytic converter30. Pedal assembly31. 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 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 solenoid valve (for 90 CV version only)4. Air conditioning compressor (where fitted)5. E.G.R. solenoid valve6. 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. 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. Fuel pressure regulator on rail26. Injectors27. Heater plugs28. Pressure regulator on the pump (for 90 CV version only)29. Heater plugs warning light30. Injection warning light31. Coolant overheating warning light32. Water in the fuel filter warning light33. OIL warning lightSelf-diagnosisThe control unit self-diagnostic system checks the signals coming from the sensors comparing them with the permitted limits.SIGNALLING OF FAULTS DURING STARTING:- Warning light on until engien 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.SIGNALLING OF FAULTS DURING OPERATION:- Warning light on indicates fault;- Warning light off indicates no fault with components that affect the safety of the system;RECOVERYFrom time to time the control unit defines the type of recovery according to the components that 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 amount of fuel injectedOn the basis of the signals coming from the sensors and the values stored, the control unit:- controls the pressure regulator on the rail;- controls the regulator on the pressure pump to modulate the fuel flow rate (for the 90 CV version only)- 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 takes the battery voltage into account.Fuel cut-off during decelerationDuring the accelerator pedal release stage, the control unit implements the following logics:- 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).Check on irregular operationThe 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 fumes 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 for the injectors.- 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. valveMaximum torque limit controlAccording to the rpm level, the control unit calculates the following in pre-defined maps:- the torque limit;- the permitted fumes (limit).It compares this minimum values and corrects them with other parameters:- coolant temperature;- engine rpm;- vehicle speed;- air temperature.and 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.Heater plugs checkThe injection unit, during the following stages:- starting;- post-starting;applies a timer to the glow plug preheating control unit based on 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 recognizes which cylinder is in the explosion stroke and controls the injection sequence at the appropriate cylinder.Pilot injection and main injection advance checkAccording to the signals coming from the various sensors, including the absolute pressure sensor integrated in the control unit itself, the latter determines the optimum injection point, according to an internal map, based on driving comfort and EURO 4 emission limits.Injection pressure closed cycle checkDepending on the engine load, determined by processing the signals coming from the various sensors, the control unit operates the regulator on the rail and the regulator on the pressure pump (for the 90 CV version only) to produce an optimum line pressure.Electrical balance checkAccording to the battery voltage, the control unit alters the idle speed:- 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.