Placement of elements of the MFI control system
1 - air flow meter "OBD"; 2 - temperature sensor of the air entering the engine; 3 - air flow meter, except "OBD"; 4 - air-fuel mixture sensor, except "OBD"; 5 - coolant temperature sensor; 6 - throttle position sensor; 7 - camshaft position sensor; 8 - crankshaft rotation angle sensor; 9 - heated oxygen sensor; 10 - fuel injectors; 11 - idle frequency modulator; 12 - vehicle speed sensor; 13 - knock sensor; 14 – the switch of ranges of a transmission; 15 - ignition lock; 16 - ECM engine control unit; 17 – the relay of an air conditioning system; 18 - solenoid valve for cleaning the canister with activated carbon; 19 - main relay MFI; 20 - ignition coils; 21 - fuel pump; 22 - acceleration sensor; 23 - diagnostic connector.
The fuel system is controlled by the ECM (Engine Control Module). The ECM regulates the ignition timing, determines the amount of fuel supplied to the engine, controls the emission control system and the engine idle speed, as well as the A/C compressor clutch, etc. The ECM changes engine operating modes in response to changing operating conditions based on signals from various switches and sensors.
For example, the ECM adjusts the ignition timing based on sensor signals that respond to engine speed, coolant temperature, throttle position, currently engaged gear, vehicle speed, and so on.
The ECM controls the idle speed based on sensor signals that respond to throttle position, vehicle speed, currently engaged gear, etc.
Air flow meter sensor "OBD" (MAF – Mass Airflow Sensor)
The air mass meter provides the most direct method to measure engine loads, as it measures the amount of air entering the engine. The air flow enters the motor through a hot and cold wire meter forming part of the bridge circuit. The current passing through the heated wire element maintains its constant temperature at a constant level, which is higher than the temperature of the air entering the engine. The mass of air is determined by the amount of current required to maintain the temperature of the wire element. The greater the air flow and, of course, its cooling, the greater the magnitude of the signal supplied to the ECM.
Intake air temperature sensor "OBD" (IAT – intake air temperature)
The engine intake air temperature sensor is a thermistor whose resistance changes with temperature. The ECM takes into account the sensor signal and adjusts the pulse width applied to the injectors, which changes the amount of fuel supplied to the engine cylinders, and also changes the ignition timing.
Sensor test
1. Measure the voltage between pins 1 and 3 of the sensor connector.
Temperature | Output voltage |
0°C | 3.3-3.7 V |
20°C | 2.4-2.8V |
40°C | 1.6-2.0 V |
80°C | 0.5-0.9V |
2. If the sensor output voltage is not as specified, replace the sensor.
Manifold absolute pressure sensor, except "OBD" (MAF – Manifold Absolute Pressure)
The intake manifold absolute pressure sensor is a sensitive variable resistor. It measures intake manifold pressure, which varies with engine operating conditions and is converted into voltage. The sensor is also used to measure atmospheric pressure when starting the engine and provides engine operation modes at different altitudes. Based on information from the sensor, the engine control unit regulates the amount of fuel supplied to the engine, and also changes the ignition timing.
Examination
1. Measure the voltage between pins 1 and 4 of the sensor connector.
- Output voltage with the ignition on and the engine off: 4-5 V
- Output voltage at idle frequency: 0.5-2.0V
2. If the sensor output voltage is not as specified, replace the sensor.
Intake air temperature sensor (IAT – intake air temperature)
The engine intake air temperature sensor is a thermistor whose resistance changes with temperature. The ECM takes into account the sensor signal and adjusts the pulse width applied to the injectors, which changes the amount of fuel supplied to the engine cylinders, and also changes the ignition timing.
Examination
1. Measure the resistance between tracks 1 and 2 of the sensor connector.
Temperature | Resistance |
0°C | 4.5-7.5 ohms |
20°C | 2.0-3.0 ohm |
40°C | 0.7-1.6 ohm |
80°C | 0.2-0.4 ohm |
2. If the sensor resistance is out of specification, replace the sensor.
Coolant temperature sensor (ECT – Engine Coolant temperature)
The coolant temperature sensor monitors the coolant temperature and, based on the sensor signal, the ECM calculates the pulse width applied to the injectors, which changes the amount of fuel supplied to the engine cylinders, as well as changes the ignition timing.
When the engine is cold, the ECM operates in open loop mode, which results in a richer air-fuel mixture entering the engine cylinders and increasing the idle speed. This continues until the engine reaches normal operating temperature.
Withdrawal
1. Remove the sensor from the engine.
2. When heating a vessel with water and a sensor located in it, check its resistance.
Temperature | Resistance |
–30°C | 22.22-31.78 kΩ |
–10°C | 8.16-10.74 kΩ |
0°C | 5.18-6.60 kΩ |
20°C | 2.27-2.73 kΩ |
60°C | 1.059-1.281 kΩ |
40°C | 0.538-0.650 kΩ |
80°C | 0.298-0.322 kΩ |
90°C | 0.219-0.243 kΩ |
3. If the sensor resistance is out of specification, replace the sensor.
Installation
1. Apply LOCTITE 962T to the sensor threads.
2. Screw the sensor into the cylinder block and tighten it to the required torque.
Tightening torque: 15–20 Nm
3. Connect the electrical connector to the sensor.
Throttle position sensor (TP – Throttle Position)
The throttle position sensor provides information that the ECM uses to determine when the throttle is closed, fully open, or in between positions. The sensor is rigidly connected to the throttle shaft. Depending on the position of the throttle valve, the resistance of the sensor changes. The ECM supplies the sensor with 5 volts to power it. The sensor output voltage varies from 0.25 volts at minimum throttle to 4.7 volts at full throttle.
Examination
1. Disconnect the connector from the throttle position sensor.
2. Measure the resistance between tracks 1 and 2 of the sensor connector.
Resistance: 0.7-3.0 kΩ
3. Connect an ohmmeter to pins 1 and 3 of the sensor connector.
4. Slowly open the throttle and check that the sensor resistance changes smoothly in proportion to the throttle opening.
5. If the resistance of the sensor differs from the required value or changes abruptly, replace the sensor.
Tightening torque: 1.5 - 2.5 Nm
Camshaft position sensor (CMP – Camshaft Position Sensor)
The camshaft position sensor generates pulses, based on which the ECM identifies the first cylinder and the injector opening time.
Crank angle sensor (CKP – Crankshaft Position Sensor)
The crank angle sensor provides the ECM with information about the position of the crankshaft. Based on the output signal information from this sensor and the signal from the camshaft position sensor, the ECM determines the ignition timing and the cylinder to be injected with fuel. If there is no sensor output, the engine will not start.
Examination
1. Disconnect the connector from the crank angle sensor
2. Measure the resistance between tracks 1 and 2 of the sensor connector.
Resistance: 0.486-0.594 kΩ at 20°C
3. If the sensor resistance is out of specification, replace the sensor.
- Gap between rotor and crank angle sensor: 0.5–1.0 mm
- Tightening torque: 9–11 Nm
Oxygen sensor
Depending on the oxygen content in the exhaust gases, the oxygen sensor induces a voltage of 0 to 1 V. Based on this data, the engine control unit changes the opening time of the injectors and the fuel ratio in the air-fuel mixture. In order for complete combustion of the combustible mixture to occur and there were no harmful substances in the exhaust gases, 1 part of fuel must fall on 14.7 weight parts of air.
The oxygen sensor is equipped with a heater that maintains the temperature of the sensor within a certain range when the engine is running in all operating modes. Maintaining a certain temperature of the sensor allows the system to start up and idle faster.
Examination
Warning! Before checking, warm up the engine until the coolant temperature is 80–95°C.
Warning! Use an accurate digital voltmeter to measure the output voltage of the sensor.
If the sensor output voltage is not as specified, replace the sensor.
Tightening torque: 50–60 Nm
Fuel injectors
Fuel injectors, based on signals from the ECM, inject fuel into the engine cylinders. The amount of fuel supplied depends on the opening time of the injectors, i.e. on the width of the voltage pulse applied to the injector winding.
Examination
1. When the engine is idling, use a stethoscope or finger to check the operation of the injectors for clicks.
2. If there are no clicks, check the reliability of connecting the connectors to the injectors and the output voltage of the control unit.
3. Disconnect the connector from the fuel injector and measure the resistance between the connector pins.
Resistance: 15.9±0.35ohm
4. Connect the connector to the fuel injector.
Knock sensor
The knock sensor responds to high-frequency oscillations of the cylinder block and converts them into electrical signals, the magnitude of which increases with increasing knock. Based on these signals, the ECM retards the ignition timing to eliminate detonation.
Fuel lines and hoses
Fuel lines and hoses transfer fuel from the fuel tank to the fuel line and injectors and return excess fuel to the tank. Fuel pipelines fixed to the bottom of the vehicle must be periodically inspected for dents and deformation, since due to the narrowing of their passages, fuel flow may be restricted.
The fuel lines and hoses also carry fuel vapor from the fuel tank to the activated charcoal canister, where it collects when the engine is off. After starting the engine and warming up to operating temperature, the engine control unit opens the solenoid valve, and fuel vapor from the canister enters the engine and is burned.