Chevrolet Niva vehicles with electronically controlled throttle valve use a fuel supply system with a drainless fuel rail
The function of the fuel supply system is to ensure the supply of the required amount of fuel to the engine in all operating modes. Fuel is supplied to the engine by injectors installed in the intake pipe.
The electric fuel pump installed in the fuel tank supplies fuel through the main fuel filter and fuel supply hoses to the injector rail.
The fuel pressure regulator built into the electric fuel pump maintains the fuel pressure supplied to the injectors within 364-400 kPa depending on the engine operating mode.
The controller turns on the fuel injectors sequentially. Each injector is activated every 720° of crankshaft rotation.
The controller signal that controls the injector is a pulse, the duration of which corresponds to the amount of fuel required by the engine.
This pulse is supplied at a certain moment of crankshaft rotation, which depends on the engine operating mode.
The control signal supplied to the injector opens the normally closed valve of the injector, supplying fuel under pressure to the intake port.
The amount of fuel supplied is proportional to the time during which the injectors are open (injection pulse duration).
The controller maintains the optimal air/fuel ratio by changing the pulse duration.
Increasing the injection pulse duration leads to an increase in the amount of fuel supplied with a constant air flow rate (enrichment of the mixture).
Decreasing injection pulse duration leads to a decrease in the amount of fuel supplied at a constant air flow rate (lean mixture).
Electric fuel pump module (EFM)
The immersion type EFM is installed in the fuel tank (Fig. 2).
The electric fuel pump module (Fig. 3) includes a turbine-type electric fuel pump, a fuel pressure regulator, a mesh filter, a coarse fuel filter and a fuel level sensor.
The pump supplies fuel from the fuel tank through the main fuel filter to the injector rail.
The electric fuel pump is switched on by the controller via a relay. When the ignition is turned on, the controller powers the relay for 2 seconds to create the required fuel pressure in the injector rail.
If the engine does not start cranking during this time, the controller switches off the relay and waits for cranking to start. After it starts, the controller turns the relay on again.
If the ignition has been turned on three times without cranking the engine, then the next activation of the electric fuel pump relay is possible only with the start of cranking.
ATTENTION.
Operating the car with an almost empty tank is not allowed, as this can lead to premature wear and failure of the electric fuel pump.
Mesh filter
The mesh filter (Fig. 4) is designed to trapping particles larger than 60 microns entering the electric fuel pump along with fuel, which can lead to a malfunction of the injection system.
The filter consists of a plastic frame covered with a polyamide cloth, a lock washer installed in a socket of the plastic housing and a sleeve covering the nozzle.
Fuel filter
The fuel filter is installed under the body bottom near the fuel tank (Fig. 5).
The filter is built into the supply line between the electric fuel pump and the fuel rail.
The filter has a steel body with fittings at both ends. The filter element is made of paper and is designed to trap particles that can cause the injection system to malfunction.
Injector rail
The injector rail is a hollow tube with injectors mounted on it.
The injector rail is secured with two bolts to the inlet pipe (Fig. 6).
Fuel under pressure is supplied to the the internal cavity of the ramp, and from there through the injectors into the intake pipe.
On the injector rail (Fig. 7) there is a nipple 1 for monitoring the fuel pressure, closed with a threaded plug.
A number of diagnostic procedures during vehicle maintenance or troubleshooting require monitoring the fuel pressure.
Using a pressure gauge connected to the nipple, you can determine the pressure of the fuel supplied to the injectors.
Fuel injectors
Injector 2 (Fig. 7) of the distributed injection system is an electromagnetic device that doses the supply of fuel under pressure to the engine intake pipe.
The injectors are secured to the rail using spring clamps.
The upper and lower ends of the injectors are sealed with sealing rings, which must always be replaced new ones when removing and installing the injectors.
The controller controls the electromagnetic valve of the injector, which passes fuel through the guide plate, providing fuel atomization.
The guide plate has holes that direct the fuel, forming a conical torch.
The fuel torch is directed at the inlet valve. Before the fuel enters the combustion chamber, it evaporates and mixes with air.
An injector with a stuck valve in a partially open state causes a loss of pressure in the injector rail after the electric fuel pump is turned off, so on some engines an increase in cranking time will be observed.
In addition, an injector with a stuck valve can cause pre-ignition, because some fuel will continue to flow into the engine after it is shut off.
Fuel Control Modes
As mentioned earlier in this chapter, the amount of fuel delivered through the injectors is controlled by the controller.
Fuel is delivered using one of two different methods: synchronous, i.e. at a certain position of the crankshaft, or asynchronous, i.e. without synchronization with the crankshaft rotation.
Synchronized fuel supply is the predominantly used method.
Synchronization of the injectors is ensured by using signals from the crankshaft position sensor and the phase sensor.
The controller calculates the moment of activation of each injector, and the fuel is injected once per one complete working cycle of the corresponding cylinder.
This method allows for more accurate dosing of fuel by cylinders and a reduction in the level of toxicity of exhaust gases.
Asynchronous fuel supply is used in the starting mode and dynamic modes of engine operation.
The controller processes the sensor signals, determines the engine operating mode and calculates the duration of the fuel injection pulse.
To increase the amount of fuel supplied, the duration of the injection pulse is increased, to decrease it, it is shortened.
The duration of the injection pulse can be monitored using the diagnostic device.
The fuel supply is controlled in one of several modes described below.
Disabling the fuel supply
Fuel supply is not performed in the following cases:
- - the ignition is off (this prevents pre-ignition);
- - the engine crankshaft does not rotate (there is no signal from the crankshaft position sensor);
- - if the controller has detected misfires in one or more cylinders, the fuel supply to these cylinders is stopped and the malfunction indicator starts flashing;
- - the engine crankshaft speed exceeds the limit value of about 6200 rpm (the fuel supply is disabled in conjunction with the throttle valve closing and lowering the ignition timing);
- - when "rolling out" in gear and when "revving" at idle in a car, if the engine speed exceeds 2000 rpm, the accelerator pedal is not pressed, the coolant temperature is above 40 °C.
Start mode
When the ignition is turned on, the controller uses a relay to turn on the electric fuel pump, which creates fuel pressure in the injector rail.
The controller processes the signal from the coolant temperature sensor to determine the injection pulse duration required for starting.
When the engine crankshaft begins to turn during starting, the controller generates a pulse to turn on the injectors, the duration of which depends on the coolant temperature, cranking time and increase in speed.
On a cold engine, the injection pulse increases to increase the amount of fuel, and on a warm engine, the pulse duration decreases.
The system operates in start mode until a certain crankshaft speed is reached (the desired speed idle speed), the value of which depends on the coolant temperature.
ATTENTION.
A necessary condition for starting the engine is to achieve an engine speed of at least 80 rpm when cranking the starter, the voltage in the vehicle's on-board network should not be lower than 6 V.
Open-loop fuel supply control mode
After starting the engine and until the conditions for entering the closed-loop mode are met (the control oxygen sensor is warmed up to the required temperature), the controller controls the fuel supply in the open-loop mode.
In the open-loop mode, the controller calculates the duration of the injection pulses without taking into account the presence of oxygen in the exhaust gases.
Calculations are made based on data on the crankshaft speed, mass air flow, coolant temperature and the requested torque (this is expressed in the position of the throttle valve, UOZ and directly in the fuel supply), which can additionally be affected by the inclusion of electrical consumers (lights, seat heating, fan, etc.).
Power enrichment mode
The controller monitors the position of the accelerator pedal and the crankshaft speed to determine the moments when maximum engine power is required.
To develop maximum power, a richer fuel mixture is required (the UOZ control mode is disabled), which is achieved by increasing the duration of the injection pulses.
Compensation for changes in on-board network voltage
When the on-board network voltage decreases, energy accumulation in the ignition coils occurs more slowly, and the mechanical movement of the injector electromagnetic valve takes longer.
The controller compensates for the drop in on-board network voltage by increasing the energy accumulation time in the ignition coil and the duration of the injection pulses.
Accordingly, when the voltage increases, in the vehicle's on-board network, the controller reduces the energy accumulation time in the ignition coil and the duration of the injection pulses.
Closed-loop fuel supply control
The system enters the closed-loop mode when all of the following conditions are met:
- - 1 The oxygen sensor is warm enough for normal operation (the "dew point" has been passed - the temperature on the ceramic of the HO2S sensor element exceeds the temperature determined depending on the ambient temperature, the output signal goes beyond the range of 300-600 mV).
- - 2 The coolant temperature is above a certain value.
- - 3 Since starting the engine, a certain period of time has run, depending on the coolant temperature at the time of starting.
- - 4 The engine does not operate in any of the following modes: engine start, fuel cut-off, maximum power mode, ECM protection mode.
- - 5 The engine operates within a certain range of the load parameter.
In closed-loop fuel control mode, the controller initially calculates the injection pulse duration based on the same sensors as for open-loop mode (basic calculation).
The difference is that in closed-loop mode, the controller uses the signal from the control oxygen sensor to adjust the injection pulse duration calculations in order to ensure maximum efficiency of the catalytic converter.
There are two types of fuel supply adjustments - current and self-learning adjustments.
The first (current) adjustment is calculated based on the oxygen sensor readings and can change relatively quickly to compensate for current deviations in the mixture composition from stoichiometric.
The second (self-learning adjustment) is calculated for each set of "speed-load" parameters based on the current adjustment and changes relatively slowly.
The current adjustment is reset each time the ignition is turned off.
The self-learning adjustment is stored in the controller memory permanently, until the "ECU reset with initialization" mode is performed using the diagnostic device.
The purpose of the adjustment based on the self-learning results is to compensate for deviations in the fuel-air mixture composition from the stoichiometric one, which arise as a result of the spread of the characteristics of the ECU elements, tolerances in the manufacture of the engine, as well as deviations in the engine parameters during operation (wear, coking, etc.).
For more accurate compensation of the deviations that arise, the entire range of engine operation is divided into 4 characteristic learning zones:
- - idle;
- - high speed at low load;
- - partial loads;
- - high loads.
When the engine is operating in any of the zones, the pulse duration is corrected according to a certain logic injection until the actual mixture composition reaches the optimum value.
When the engine operating mode is changed, the last value of the correction factor for this zone is saved in the controller's random access memory (RAM).
The correction factors obtained in this way characterize a specific engine and are used in calculating the injection pulse duration when the system is operating in open loop mode and at start-up, without being able to change.
The correction value at which closed-loop fuel supply regulation is not required is 1 (for the fuel supply correction parameter based on the results of self-learning at idle, it is 0).
Any change from 1(0) indicates that the closed-loop fuel supply regulation function changes the injection pulse duration.
If the closed-loop fuel supply correction value is greater than 1(0), the injection pulse duration increases, i.e. increase in fuel supply.
If the closed-loop fuel supply correction value is less than 1(0), the injection pulse duration is reduced, i.e. the fuel supply is reduced.
The maximum range of change of the current fuel supply correction and self-learning correction is the range of 1±0.25 (±5).
If any of the correction factors goes beyond the regulation limits towards enrichment or leanness of the mixture, this indicates a malfunction in the engine or ECM (deviation in fuel pressure, air leak, leak in the exhaust system, etc.).
Self-learning correction for regulating fuel supply on vehicles with a catalytic converter is a continuous process throughout the entire service life of the vehicle and ensures compliance with strict exhaust gas toxicity standards.
In this ECM, when the battery is disconnected, the values of the adaptation correction factors are not reset.