312000296 - INTRODUCTION - DIESEL FUEL INJECTION SYSTEM
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 1400 bar);
- The possibility of modulating pressures from 150 bar up to a maximum service pressure of 1400 bar, regardless of engine rpm and load;
- ability to work at high engine rpms (up to 5000 rpm in full load conditions);
- injection control precision (injection advance and duration);
- reduced fuel consumption;
- reduced emissions.
The main system functions are as follows:
- fuel temperature control;
- engine coolant temperature control;
- control of amount of fuel injected;
- idle speed control;
- fuel cut-off during over-run;
- cylinder balance check when idling;
- control of anti-judder function;
- control of exhaust fumes during acceleration;
- exhaust gas recirculation control (E.G.R.);
- maximum torque limit control;
- maximum speed limit control;
- glowheater plug control;
- control of climate control system activation (where fitted);
- auxiliary fuel pump control;
- cylinder position check for timing;
- main and multiple injection advance control;
- closed cycle injection pressure control;
- electrical balance control;
- IMA injector calibration.
- DPF regeneration control (where present)
Introduction
The 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;
- turbocharging pressure;
- air temperature (from flow meter);
- intake air quantity;
- battery voltage;
- diesel pressure;
- accelerator pedal position;
- diesel temperature.
Self-diagnosis
The control unit self-diagnostic system checks the signals coming from the sensors and compares them with the permitted limits.FAULT SIGNALS DISPLAYED DURING START UP:
- 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 a fault;
- warning light off indicates no fault with components that affect the safety of the system;
Fiat CODE recognition
The 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 control
With 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 control
When the engine coolant temperature is above 105°C, the control unit:
- reduces the quantity of fuel injected (reduces engine power);
- controls the cooling fans;
- switches the coolant temperature warning light on.
Control of the amount of fuel injected
The control unit compares the signals coming from the sensors to the stored values, and:
- controls the pressure regulator;
- varies the "pilot" injection time in the entire rpm range;
- modulates the "main" injection time.
Idle speed check
The control unit processes the signals coming from the various sensors, regulates the quantity of fuel injected and:
- controls the pressure regulator;
- modulates the injector injection times.
Fuel cut-off during over-run
When the accelerator pedal is released, the control unit implements the following strategies:
- Places the injection 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 check.
According to the signals received from the sensors, the control unit controls the idle speed torque:
- modulates the quantity of fuel injected into the individual injectors (injection time).
Anti-judder check
The 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 acceleration
In order to restrict the fumes during fast transitions, on the basis of the signals received from the accelerator pedal potentiometer, flow meter and the engine speed the control unit limits the amount of fuel to be injected by means of:
- the pressure regulator
- the injector injection time.
Exhaust gas recirculation control (E.G.R.)
In accordance with EURO 3/4 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:
- adjusting the E.G.R. valve opening.
Maximum torque limit control
The control unit uses mapped values plotted against rpm to calculate the following:
- the torque limit;
- the permitted level of fumes (limit).
It compares these minimum values with other parameters and corrects them:
- coolant temperature;
- engine rpm;
- vehicle speed;
- air temperature,
Maximum speed limit control
When the engine speed reaches 5200 rpm, the control unit interrupts the operation of the injectors and the supply pressure is consequently reduced.
Glowheater plug check
The injection control unit, during the following stages:
- start-up;
- post start-up
- times the operation of the glowheater plug control unit on the basis of engine temperature.
Air conditioning system start-up check
The control unit operates the climate control compressor:
- activating/de-activating it when the correct 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 check
Irrespective of the rpm, the control unit:
- supplies the auxiliary fuel pump when the key is turned to MAR;
- cuts off the auxiliary pump supply if the engine is not started within a few seconds.
Cylinder position check
During 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 check
According 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 3/4 emission limits.
Injection pressure closed loop check
The control unit controls the regulator to produce optimum line pressure according to engine load, which is determined by processing signals from the various sensors.
Electrical balance check
The control unit modulates idle speed according to the battery voltage and:
- increases the injector injection times;
- modulates the line pressure.
Fan control
Depending on the temperature of the engine coolant and the pressure of the air conditioning system coolant, the control unit controls:
- fan activation at first or second speed.
Fuel cut off function
There is no inertia switch on th
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