3356174 - INTRODUCTION - PETROL FUEL INJECTION SYSTEM
CONSTRUCTION SPECIFICATIONS
The Marelli IAW 5NF system (5SF for the Z 16 XEP engine) belongs to the category of systems integrated with:
- inductive discharge, digital, electronic ignition
- static advance
- sequential, phased type electronic injection (1-3-4-2).
Operation of the injection/ignition system
In engine idle conditions, the control unit controls:
- the moment of ignition
- the air flow rate with the benefit of maintaining smooth engine operation even when environmental and applied load parameters change.
The system functions are essentially as follows:
- system self-adaptation
- self-diagnostics
- Fiat CODE recognition
- cold starting check control
- control of combustion - Lambda sensors
- detonation control
- check on enrichment during acceleration
- fuel cut-off during deceleration
- fuel vapour recovery
- restriction of maximum rpm
- fuel pump control
- connection with climate control system
- cylinder position recognition
- injection time adjustment
- ignition advance adjustment
- control and management of idle speed
- control of cooling fan.
Injection system
The essential conditions to be met by the air-fuel mixture for efficient operation of engines with controlled ignition systems are mainly as follows:
- the metering (air/fuel ratio) must be kept as close as possible to stoichiometric value to ensure that combustion is as fast as possible avoiding fuel wastage
- the homogeneity of the mixture, consisting of petrol vapours distributed throughout the air as finely and uniformly as possible.
Ignition system
The ignition circuit is the static, inductive discharge type, i.e. without a HT distributor, with power modules located inside the injection -ignition control unit.On this system there is a coil for each cylinder connected directly to the spark plug.The primary winding for each coil is connected to the power relay (thereby receiving the battery voltage supply) and to the pins of the electronic control unit for earthing.After the starting stage, the electronic unit manages the basic advance taken from a special map in accordance with:
- engine rpm
- absolute pressure value (mbar) measured in the intake manifold.
Diagram showing information entering/leaving the control unit
The fuel level and engine oil pressure information reaches the control unit via the CAN line.
Operating strategies
System self-adjustment
The control unit is equipped with a self-adjustment function that is designed to recognize the changes that take place in the engine due to the processes of bedding in and ageing of both the components and the engine itself in time.These changes are memorized in the form of modifications to the basic map and are designed to adapt the operation of the system to the gradual alterations in the engine and the components compared with when they were new.This self-adjustment function also makes it possible to compensate for the inevitable differences in any replacement components (due to production tolerances).The control unit modifies the basic map in relation to engine specifications when new on the basis of an exhaust gas analysis.The self-adjustment parameters are not deleted if the battery is disconnected.Self-diagnosis
The control unit auto-diagnostic system checks that the system is working properly and signals any irregularities by means of an MIL warning light in the instrument panel with a standardized ideogram and colour laid down by European regulations.This warning light indicates engine management faults and also faults detected by EOBD diagnostic strategies.The MIL warning light operating (mil) strategy is as follows:
- with the ignition on, the warning light comes on and remains on until the engine has been started up.
- The control unit self-diagnostic system checks the signals coming from the sensors comparing them with the permitted limits.
Fault indication during start up:
- the failure of the warning light to go out when the engine has been started indicates that there is an error memorized in the control unit.
Fault indication during operation:
- the warning light comes on in flashing mode to indicate possible catalytic converter damage due to misfiring.
- the warning light comes on in constant mode to indicate the presence of engine management or EOBD RECOVERY diagnostic errors.
Fiat code recognition
The moment the control unit receives the ignition ON signal it converses with the Body Computer (Fiat CODE function) to obtain the go ahead for starting.The communication takes place via the CAN line that connects the two control units.
Recognition of cylinder position
The engine timing sensor, together with the engine rpm and top dead centre (TDC) signal, allows the control unit to recognise cylinder sequence when implementing phased injection.This signal is produced by a Hall effect sensor, positioned on the tappet cover near the flywheel on the camshaft pulley.
Combustion - lambda sensor check
On EOBD systems the Lambda sensors, all the same type but not interchangeable, are positioned one before (pre) the catalyzer system and one after (post) the catalytzer.The pre-catalyzer sensor determines the control of the mixture strength known as the 1st closed loop for the upstream sensor.The post-catalyzer sensor is used for the fault diagnosis of the catalyzer and for modulating the 1st loop control parameters.The second loop is therefore adaptive to make up for production discrepancies and slight drift that pre-catalyzer sensor responses could experience due to ageing and contamination.This control is known as 2nd loop control (post-catalyzer sensor closed loop).
Operation when cold
In these conditions there is a natural weakening of the mixture as a result of the poor turbulence of the particles of fuel at low temperature, reduced evaporation and strong condensation on the internal walls of the intake manifold, all of which is exacerbated by the increased viscosity of the lubricant oil which, as is known, increases the rolling resistance of the engine mechanical components at low temperatures.The electronic control unit recognizes this condition on the basis of the coolant temperature signal, increasing the basic injection time.
Operation in full load conditions
The full load condition is detected by the control unit by means of the throttle position and absolute pressure values.In full load conditions the basic injection time must be increased to create the maximum power supply produced by the engine.
Operation in deceleration
The engine has two overlapping strategies during this stage:
- A negative transition strategy to keep the quantity of fuel supplied to the engine at the stoichiometeric level (less pollution). This stage is recognized by the control unit when the throttle position signal goes from a high voltage value to a lower one.
- A soft accompaniment strategy at low speed (dash-pot) to dampen the variation in torque supplied (reduced engine braking).
Operation in acceleration
In this stage the control unit increases the amount of fuel supplied to the engine (to produce the maximum torque) depending on the signals:
- throttle position;
- rpm and T.D.C. signal
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recovery
Air temperature sensor
If the error is present during starting:
- it assumes a value of 50 °C
- the mixture strength self-adjustment is inhibited.
If the error is present in other conditions:
- the last valid value is memorized and updated depending on the engine temperature.
Detonation sensor
If this sensor is faulty, the engine management control unit implements the most conservative ignition advance maps to safeguard the engine.Pressure sensor
If the error is present during starting, a value of 1024 mbar is used.During operation the value is calculated on the basis of the parameters supplied by the throttle position and rpm sensors.The mixture strength self-adjustment is inhibited.Vehicle speed sensor
The last vehicle speed value memorized is used.Coolant temperature sensor
If there is a fault, the control unit inhibits the mixture strength self-adjustment and idling.Setting the last temperature value measured; if it does not correspond to the operating temperature, the control unit increases it gradually depending on the time since the engine has been started until the theoretical figure of 80°C is reached.In addition, when the ignition key is inserted, the radiator cooling fan is activated permanently at the second speed.IAW 5NF injection/ignition control unit (5SF for Z 16 XEP engines)
The control unit is fitted in the engine compartment on the intake manifold chamber and is capable of withstanding high temperatures.It is a digital type unit with a microprocessor featuring a high calculation capacity and is accurate, reliable, versatile, with low energy consumption and is maintenance-free.The task of the electronic unit is to process the signals coming from the various sensors through the application of software algorithms and to control the operation of the actuators (in particular the injectors, ignition coils and idle actuator) in order to ensure the best possible operation of the engine.The adoption of the Fiat CODE means that control units cannot be swapped between vehicles.Pin out
The diagram below shows the control unit pin out.
Injectors
Specifications
The injectors are the miniature type (Pico) with a 12 V supply and an internal resistance of 13.8 - 15.2 ohm at 20°C.The injectors are fastened by the manifold which presses against them in their seats in the intake manifold ducts, whilst the two fluorine rubber seals (1) and (2) provide a seal on the inlet manifold and the fuel manifold.The fuel supply takes place from the top (3) of the injector whose body contains the winding (4) connected to the terminals (5) of the electrical connector (6). | Do not apply stress to the injector manifold during the removing-refitting operations as it could adversely affect its operation. |
Operation
The jet of fuel comes out of the injector at an absolute pressure of 3.5 bar through the returnless system atomizing immediately.The injector control logic is the phased sequential type, i.e. the four injectors are operated in accordance with the inlet stages.FUEL MANIFOLD
Specifications
The fuel manifold is fastened to the inner part of the intake manifold and its function is to transfer the fuel to the injectors.In addition to the seats for the injectors there is a rapid connector on the fuel manifold for connection with the fuel supply pipe and a connector for checking the fuel supply pressure.
Engine COOLANT temperature sensor
Specifications
This is fitted to the thermostat cup and detects coolant temperature by means of an NTC thermistor with negative resistance coefficient.Electrical properties| °C | O |
|---|---|
| -20 | 15971 |
| -10 | 9620 |
| 0 | 5975 |
| 10 | 3816 |
| 20 | 2502 |
| 25 | 2044 |
| 30 | 1679 |
| 40 | 1152 |
| 50 | 807 |
| 60 | 576 |
| 70 | 418 |
| 80 | 309 |
| 90 | 231 |
| 100 | 176 |
Operation
The reference voltage is 5V for the NTC element for the injection system. Because the control unit input circuit is designed as a voltage divider, this voltage is distributed between a resistance present in the control unit and the sensor NTC resistance.The control unit is therefore able to assess sensor resistance changes via changes in the voltage and thus obtain temperature information.
Composition
The sensor components are:
Detonation sensor
Specifications
The piezoresistive type detonation sensor is fitted on the crankcase between and measures the intensity of vibrations caused by knock in the combustion chambers.This phenomenon has mechanical repercussions on a piezoelectric crystal that sends a signal to the control unit which, on the basis of this signal, reduces the ignition advance until the phenomenon disappears.The control unit restores the advance gradually until the optimum operating value is reached.
Operation
The molecules of a quartz crystal are electrically polarised.In rest condition (A), the molecules do not display any particular orientation.When the quartz crystal is subject to pressure or impact (B), the degree of alignmnent is directly proportional to the pressure acting on the crystal.This orientation generates a voltage at the crystal terminals.
Rpm sensor
Specifications
It is fitted on the cylinder block/crankcase facing the flywheel on the crankshaft pulley.It is inductive type, i.e. its operation is determined by magnetic field changes generated by the teeth passing in front of the phonic wheel (602 teeth).The injection control unit uses the rpm signal for:
- determining the rotation speed of the crankshaft
- determining the angular crankshaft position.
Composition
The sensor takes the form of a tubular case (1) containing a permanent magnet (3) and an electrical winding (2).
Operation
Due to the passage of the phonic wheel teeth, the magnetic flux set up by magnet (3) undergoes fluctuations due to changes in the gap.These fluctuations set up an electromotive force in winding (2) and a voltage is set up at the terminals that is alternatively positive (tooth facing sensor) and negative (gap facing sensor).The rpm sensor peak output voltage depends, all else being equal, on the distance between the sensor and the phonic wheel teeth (gap).There are sixty teeth on the flywheel, with two having been removed to produce a reference: the passing of the wheel therefore corresponds to an angle of 6° (360° divided by 60 teeth).The synchronism point is recognised at the end of the first tooth following the gap left by the two missing teeth: when this passes beneath the sensor, the crankshaft is located with piston pair 1-4 at 114° before TDC.
Accelerator pedal potentiometer
Specifications _ -the accelerator pedal is equipped with two built-in potentiometers: *- a main one *- a stand-by one.
The injection control unit implements the following recovery strategies in the following conditions:
- if one of the two potentiometers fails, this allows the throttle to be opened to a maximum of 40° over a long time period;
- if both potentiometers fail completely, it prevents throttle opening.
Operation
The sensor consists of a case secured to the accelerator pedal support. This contains an axially-located shaft connected to a dual-track potetiometer.A coil spring on the shaft ensures the correct amount of resistance to pressure while a second spring ensures return following release.Operating field from 0° to 70°; mechanical stop at 88°.
Throttle body
Specifications
This is fitted on the intake chamber inlet and regulates the amount of air taken in by the engine.According to the signal received from the accelerator pedal potentiometer, the injection control unit controls the throttle opening by means of a direct current motor built into the throttle body.Throttle opening takes place from 0° to 82°, i.e. including idle speed adjustment range. - The throttle body is equipped with two built-in potentiometers, each of which controls the other.If there is a fault with the two potentiometers or no power supply, depending on the position of the accelerator pedal, the control unit applies a recovery strategy with the consequent inferior operation noticeable to the driver and the EOBD fault diagnosis is disabled.The self-learning procedure does not have be carried out if the injection control unit or the air chamber or the throttle casing is replaced.
Operation _ -the opening of the throttle is managed by an electrically operated motor.
The Marelli 5NF (5SF for Z 16 XEP engines) system operates the motorized throttle according to accelerator pedal requests; a potentiometer is connected to it that sends a voltage signal to the control unit where it is processed and opening laws are produced.The position of the throttle is controlled by the control unit via a potentiometer incorporated in the throttle casing.INTAKE AIR TEMPERATURE AND PRESSURE SENSOR
Specifications
The pressure and intake air temperature sensor is an integral component which is designed to measure the pressure and the temperature of the air inside the intake manifold. Both pieces of information are used by the injection control unit in defining the quantity of air drawn in by the engine and are then used for calculating the injection time and the ignition point. The sensor is fitted on the intake manifold.
IGNITION COILS
Composition
The coils are connected directly to the spark plugs and are the closed magnetic circuit type. They consist of a lamellar pack with a central silicon steel core broken by a fine gap that holds both the windings.The windings are covered by a pressed plastic container and are insulated through immersion in an epoxide resin and quartz compound that gives them excellent dielectric, mechanical and also thermal properties on exposure to high temperatures. The proximity of the primary winding to the magnetic core reduces the magnetic flux losses ensuring the maximum coupling on the secondary winding.Electrical properties:Primary circuit resistance: 0.52-0.62 ohm at 23°CSecondary circuit resistance: 6830-7830 ohm at 23°C.Vehicle speed sensor
Specifications
The sensor is located on the differential output, by the left driveshaft coupling and transmits the vehicle speed signal to the body computer which, in turn, makes this signal available to the CAN.The control unit takes information relating to the vehicle speed: the signal is also used for the operation of the speedometer.The Hall effect type sensor transmits 16 impulses/rev; it is therefore possible to determine the speed of the vehicle from the frequency of the impulses. | on versions with ABS, the vehicle speed signal is produced by the ABS control unit transmitting information to the body computer which makes it available to the injection control unit via the CAN. |
TIMING SENSOR
Specifications
This system uses a phased sequential injection system, in other words the injection of the fuel takes place in sequence for each cylinder during the inlet stage.To achieve this, the electronic control unit also uses a timing signal, in addition to the rpm and TDC signal, to determine the injection point. The signal sent to the control unit is produced by a Hall effect sensor (2) fitted by the inlet side camshaft drive pulley.
