The engine control unit (ECU), also known as the engine control module (ECM), uses various sensors and inputs to determine the amount of fuel injected into the engine's cylinders. The process involves monitoring engine conditions in real-time and adjusting fuel injection accordingly. Here's a general overview of how the ECU calculates fuel injection:
① Air flow measurement:
A mass air flow (MAF) sensor or manifold absolute pressure (MAP) sensor measures the airflow into the engine. The ECU uses this information to determine the amount of air entering the combustion chamber.
② Engine speed (RPM) detection:
A crankshaft position sensor (CKP) or similar sensor provides data on engine speed (RPM). The ECU uses RPM data to determine the engine's operating status and fuel injection timing.
③ Throttle position:
The Throttle Position Sensor (TPS) informs the ECU of the position of the throttle plate. This data helps the ECU understand the driver's power needs, whether idling, cruising, or accelerating.
④ Engine temperature:
The engine coolant temperature (ECT) sensor monitors the temperature of the engine coolant. The ECU takes engine temperature into account when calculating the air-fuel mixture because a cold engine requires a richer mixture for efficient combustion.
⑤ Oxygen sensor (O2 sensor):
Oxygen sensors in the exhaust system measure the amount of oxygen in the exhaust gases. The ECU uses this data to determine if the air-fuel mixture is too rich or lean and adjusts fuel injection accordingly.
⑥ Intake air temperature:
The intake air temperature (IAT) sensor measures the temperature of the incoming air. The density of cold air is larger, which affects the air-fuel ratio, and the ECU adjusts accordingly.
⑦ Air pressure:
Barometric pressure (BARO) sensors measure atmospheric pressure. This information, combined with other sensor data, helps the ECU adjust fuel injection based on changes in altitude.
Check the outside of the injector for any signs of leakage, corrosion or physical damage. Make sure the injector seals are in good condition.
② Resistance test:
Use a multimeter to measure the resistance of each injector. Compare the resistor value to the manufacturer's specifications. Abnormal readings may indicate a faulty injector coil.
③ Fuel injector leakage test:
Perform an injector leak test to check for leaks when the injector is turned off. This can be done with a specialized injector tester or by applying vacuum to the injectors and monitoring the pressure drop.
④ Cleaning the fuel injector:
Use a professional injector cleaning kit or take the injectors to a specialized service facility for cleaning. Deposits and contaminants can affect injector performance.
⑤ Fuel pressure test:
Perform a fuel pressure test to ensure the fuel pressure meets the manufacturer's specifications. Low fuel pressure can affect injector performance.
⑥ OBD-II diagnosis:
Use an OBD-II scanner to check for injector-related fault codes. Some problems, such as misfires, can be caused by injector problems.
⑦ Visual inspection of spark plugs:
Check the spark plugs for signs of uneven combustion or fouling, which may indicate an injector problem affecting a specific cylinder.
