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The fuel injector is an electronically-controlled valve that is supplied with pressurised fuel from the fuel pump. The speed at which the injector opens and closes is controlled by the electronic control unit (ECU) using a PWM (Pulse Width Modulation) technique. The ECU is the brain of the fuel injection system and determines the appropriate amount of fuel to be injected into the engine. It receives input from various sensors, including the crankshaft and camshaft sensors, to calculate the injection pulse width, which refers to the duration the injector is open. The ECU controls the injector pulse by switching the ground circuit of the injector on and off depending on the engine's requirements.
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What You'll Learn
The Engine Control Unit (ECU)
Based on the data gathered, the ECU calculates the injection pulse width, which refers to the duration for which the injector is open. This calculation ensures the desired air/fuel ratio is achieved in each cylinder, improving engine performance and reducing exhaust emissions. The ECU then sends electrical signals to each injector, opening the needle valve and allowing fuel to be sprayed into the engine's intake manifold. This fuel is mixed with air, creating a combustible mixture.
The ECU controls the injector pulse by switching the ground circuit of the injector on and off, depending on the engine's requirements. If the injector ground circuit is activated, the fuel is sprayed onto the intake valve. The ECU uses a Pulse Width Modulation (PWM) technique to control the speed at which the injector is opened and closed. This technique ensures that the injector opens and closes at very high speeds, optimising fuel delivery.
In some cases, the ECU may encounter issues and require replacement or expert attention. For example, if there is no injector pulse or spark, it could indicate a problem with the ECU. A simple diagnostic tool called a NOID light can be used to detect digital signals from the ECU. If there is no LED flashing during cranking, it confirms that there are no pulses coming from the ECU. Additionally, an ohmmeter can be used to measure the resistance between the injector's terminals, helping to identify any potential issues with the solenoids.
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The crankshaft and camshaft sensors
The Engine Control Unit (ECU) is the brain of the fuel injection system. It receives input from various sensors, including the crankshaft and camshaft sensors, to determine the appropriate amount of fuel to be injected into the engine. The ECU controls the fuel injector pulse by gathering data from various sensors along the fuel line.
The crankshaft position sensors monitor the ignition timing, the RPM signal, and the relative engine speed. This sensor negates the need for manual distributor timing. The camshaft position (CMP) sensor determines which cylinder is firing and synchronizes the fuel injector and coil firing sequence. It tells the PCM (Powertrain Control Module) whether the #1 cylinder is on the compression stroke or the exhaust stroke. All timing (ignition and injector) is referenced by the PCM to the crankshaft position (CKP) sensor.
The ECU uses the data from the crankshaft and camshaft sensors, as well as other input parameters such as engine load and temperature, to calculate the injection pulse width, which refers to the duration during which the injector is open. The ECU sends electrical signals to each injector, which opens the needle valve within the injector to allow fuel to be sprayed into the engine's intake manifold. This fuel is mixed with air to create a combustible mixture.
In most modern fuel injection systems, injectors are typically fired sequentially and individually for each cylinder, enhancing fuel efficiency. The ECU can give the desired air/fuel ratio to any of the possible cylinders, in addition to the homogeneous distribution of fuel on each cylinder. This setting increases engine performance and reduces exhaust emissions.
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The engine load and temperature
The Engine Control Unit (ECU) is the brain of the fuel injection system. It determines the injector pulse width, which refers to the duration for which the injector is open, based on information received from various sensors, including the crankshaft and camshaft sensors. The ECU controls the injector pulse by switching the ground circuit of the injector on and off depending on the engine's requirements. For example, if the injector ground circuit is on, the fuel is sprayed onto the intake valve.
The ECU receives data on parameters such as engine load and temperature to calculate the appropriate pulse width. The engine load and temperature are crucial factors in determining the optimal amount of fuel injected into the engine. By taking these factors into account, the ECU ensures that the engine receives the right amount of fuel to meet performance and fuel consumption goals.
The engine load refers to the amount of work the engine is performing at a given time. This load varies depending on factors such as the vehicle's speed, acceleration, and the grade of the road. For instance, the engine load is higher when a vehicle is climbing a steep hill compared to driving on a flat surface. The ECU adjusts the injector pulse width accordingly to provide the required amount of fuel for the increased load.
The engine temperature is another critical factor influencing the injector pulse. As the engine temperature rises, the density of the air-fuel mixture decreases, affecting combustion. To compensate for this, the ECU may increase the injector pulse width to deliver more fuel, maintaining the optimal air-fuel ratio for efficient combustion. Conversely, at lower engine temperatures, the ECU may reduce the pulse width to inject less fuel, ensuring a proper balance.
By considering the engine load and temperature, the ECU can fine-tune the injector pulse width to optimize engine performance, fuel efficiency, and emissions. This adaptive capability of modern fuel injection systems represents a significant advancement over older mechanical injection systems, which struggled to adapt to varying working conditions.
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The Ne, G, and IGf signals
The Ne Signal
The Ne Signal is used to produce an injection drive signal. This signal is necessary for the ECU to function. In other words, the ECU cannot pulse the injector without the Ne signal and will not start or run if this signal is missing. In a 1987 Toyota Pickup 22RE, the Ne signal is generated by the Distributor/Igniter and is used to time the ignition coils.
The G Signal
The G signal is used to determine the timing of the injection signals. If the G signal is not present while the engine is cranking, the ECU will not be able to identify when to produce the injection signal, resulting in no injection pulse. However, if the ECU loses the G signal while the engine is already running, the engine will continue to run because the timing of the injection signals is locked in.
The IGf Signal
The IGf signal is monitored for fuel delivery fail-safe. If the IGf signal is not present, the ECU will go into fuel fail-safe mode by stopping injection pulses. With Conventional EFI, the IG signal is used to produce the injection drive signal. IGF stands for various terms, including "Ignition Ground Feed," "Ignition Feedback," "Ignition Failure Sensor," and "Intake Gas Flow." It is used to reference the wiring between the ignition coil and the ground in a coil pack, to transmit feedback information from various ignition components, and to detect ignition failure and shut off the fuel system to prevent engine fires.
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The Pulse Width Modulation (PWM) technique
The PWM technique is advantageous as it requires less power to drive the fuel system, freeing up energy for other operations such as air conditioning, lighting, and the blower motor. It also reduces the likelihood of fuel leaks, as there is no return line from the fuel rail, which was a potential failure point in traditional fuel pump designs.
However, there are some challenges with PWM fuel pumps. Diagnosis and testing are more complex and require specialised tools such as a live-monitoring scan tool or a digital storage oscilloscope. The additional sensors and control modules in PWM systems also introduce potential failure points, although the expected failure rate is lower than in traditional fuel pumps.
To test a PWM fuel pump, a live-monitoring scan tool or a digital storage oscilloscope must be used as typical fuel system diagnosis equipment is incompatible. The pulse width modulated voltage signal can be observed on a scope, appearing as a square wave as the voltage switches on and off.
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Frequently asked questions
The injector pulse is the period during which the injector is open and fuel is released.
The Engine Control Unit (ECU) controls the injector pulse. The ECU is the 'brain' of the fuel injection system and uses input from various sensors to determine the appropriate amount of fuel to be injected into the engine.
If you suspect a faulty injector pulse, you can use a multimeter or a noid light to test the injectors. If you do not see any voltage spikes or the noid light does not blink, it indicates a faulty injector pulse.
