Fuel Injection Operation

The Powertrain Control Module (PCM) controls the amount of fuel the fuel injector supplies to each cylinder by controlling the ON time, length of pulse, of each individual injector. The delivery timing of the fuel into the cylinder head intake port by the fuel injector is controlled by the PCM. The timing and pulse of the fuel injectors is carefully calculated with inputs from the various sensors, so that a suitable air/fuel mixture is supplied to the engine for every driving condition.

There are two types of injection timing. One is synchronous injection, when fuel injection is synchronous with the ignition signal, or the signal from the Camshaft Position (CMP) sensor. The other is asynchronous injection, when fuel injection takes place independently of the ignition signal, or the signal from the CMP sensor.

The PCM first calculates the correct timing of the fuel injectors by factoring the engine speed and the air volume together. Then the PCM applies certain compensations that are based on the information provided by various sensors that detect the state of the engine and the current driving conditions.

Synchronous Injection
When starting the engine, the fuel injectors inject the fuel simultaneously and synchronously at every CMP sensor signal. When the engine is starting at a cold state, the amount of fuel is determined by the Engine Coolant Temperature (ECT) sensor and is divided and injected.

Once the engine is running, the fuel injection occurs in a cylinder only when it is in the exhaust stroke. The powertrain control module (PCM) detects the compression stroke of the number 1 cylinder through the CMP sensor signal.

Asynchronous Injection
Whenever a change in the throttle valve opening exceeds a specified value (as determined by the PCM), additional fuel is injected simultaneously into the cylinders which are in the intake and exhaust strokes. This is in addition to the above synchronous injection and is not based on the ignition signal.

Engine Starting Enrichment
In order to improve starting performance, fuel enrichment during start up is carried out. For a certain time after the engine is started, the air/fuel mixture is enriched slightly in order to stabilize the engine speed. The amount of compensation varies depending on the engine coolant temperature as measured by the ECT sensor.

Engine Warm-Up Enrichment
When the engine is cold, additional fuel is added in order to ensure good driveability. The level of enrichment of the air/fuel mixture is gradually decreased until the ECT sensor reaches a specified value.

Acceleration Enrichment
During acceleration, the pulse of the fuel injectors is lengthened in order to deliver more fuel. The additional fuel required is relative to the engine coolant temperature. Acceleration enrichment ensures smooth and reliable engine acceleration.

Power Enrichment
In order to provide maximum power during high engine load driving conditions, the air/fuel mixture is enriched when the throttle valve opening is more than a specified, PCM determined, value.

System Voltage Compensation
A power supply system voltage drop will delay the mechanical operation of the fuel injector. The actual injector ON time becomes shorter when the system voltage decreases. In order to compensate for this, the fuel injector pulse width signal is lengthened.

Base Air/Fuel Ratio Compensation
The base air/fuel ratio may vary due to differences in individual engines and mileage. In order to compensate for such variations, feedback information is used to adjust the base air/fuel mixture to maintain the optimum air/fuel ratio.