For 1990-2009 cars

### Fuel Injector Operation

The powertrain control module (PCM) controls the amount of fuel the fuel injectors supply to each cylinder by controlling the ON time (length of pulse) of the fuel injector. The PCM also controls the timing of the delivery of the fuel by the fuel injectors. The timing and pulse of the fuel injectors is carefully calculated with input from the various information sensors. Precise control ensures 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 and the other is asynchronous injection. Synchronous injection is when the injection of fuel occurs at the same time (synchronous) as the ignition signal (or the signal from the camshaft position [CMP] sensor). Asynchronous injection is when the injection of fuel occurs independently of the ignition signal (or the signal from the camshaft position [CMP] sensor).

The PCM first calculates the volume of air and then factors in the engine speed in order to determine the correct timing of the fuel injectors. The PCM also applies certain compensations that are based on the information provided by the various information sensors that detect the state of the engine and the current driving conditions.

### Synchronous Injection

The fuel injector normally injects fuel at every ignition signal (or at every signal from the camshaft position [CMP] sensor). But when the engine coolant temperature (ECT) is low, the injection time for one ignition cycle is divided into two cycles and injection takes place accordingly. This can occur immediately after a cold engine start.

### Asynchronous Injection

Whenever a change in the throttle valve opening exceeds a specified value, the powertrain control module (PCM) pulses the fuel injectors in order to deliver additional fuel. The extra fuel 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 the compensation varies depending on the engine coolant temperature as measured by the engine coolant temperature (ECT) sensor.

### Engine Warm-Up Enrichment

Additional fuel is added in order to ensure good driveability when the engine is cold. The level of enrichment of the air/fuel mixture is gradually decreased until the engine coolant temperature (ECT) sensor reaches a specified value.

### Acceleration Enrichment

In order to deliver more fuel during acceleration, the pulse of the fuel injector is lengthened. The additional fuel required for acceleration is relative to the engine coolant temperature. Acceleration enrichment ensures smooth and dependable engine acceleration

### Power Enrichment

In order to provide maximum power during high engine load driving conditions, the air/fuel mixture is made richer. Power Enrichment is based off the manifold absolute pressure (MAP) sensor input, engine coolant temperature (ECT) sensor input and throttle position (TP) sensor input.

### Deceleration Enleanment

In order to obtain the desired air/fuel mixture ratio during deceleration, the PCM will almost eliminate fuel delivery when the manifold absolute pressure (MAP) sensor indicates that the engine has a little or a no load condition.

### System Voltage Compensation

A power voltage drop delays the mechanical operation of the fuel injector. The actual injection time becomes shorter for the time that electricity is supplied to the fuel injector. In order to compensate for this the fuel injector pulse 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. The adjustment in the base air/fuel mixture will maintain the optimum air/fuel ratio.

### Fuel Cutoff

Fuel injection stops (the operation of the fuel injectors is inhibited) when decelerating (i.e., when the throttle valve is at idle position and the engine speed is high). Stopping fuel delivery will prevent unburned gas from being exhausted. Fuel injection starts again when the above conditions are no longer present.

Fuel delivery also stops when the engine speed exceeds 7,000 RPM. Stopping fuel delivery will prevent engine overrun which adversely affects the engine. Fuel delivery starts again when the engine speed decreases to less than 6,800 RPM.

### Air/Fuel Ratio Feedback Compensation (Closed Loop Operation)

In order to obtain efficient performance of the three-way catalytic converter (TWC) and a high clarification rate of CO, HC and NOx in the exhaust gas stream, the air/fuel mixture must be kept as close to the theoretical air/fuel ratio (14.7:1) as possible. In order to accomplish this the powertrain control module (PCM) first compares the input voltage from the heated oxygen sensor 1 (HO2S 1) with a specified reference voltage. If the HO2S 1 input voltage is higher than the specified reference voltage, the PCM determines that the air/fuel ratio is richer than the theoretical air/fuel ratio and reduces the fuel (lean command). If the input voltage from the HO2S 1 is lower than the specified reference voltage, the PCM determines that the air/fuel ratio is leaner and increases the fuel (rich command). By repeating these operations, the PCM can adjust the air/fuel ratio in order to be closer to the theoretical air/fuel ratio. Control of the fuel delivery system as just described is known as Closed Loop operation.

#### Closed Loop Fuel Control Operation

Air Fuel Mixture | Exhaust O2 Content | HO2S1 Output | Fuel System Response
--- | --- | --- | ---
Lean Mixture | High Oxygen | Low Voltage | Rich Command
Rich Mixture | Low Oxygen | High Voltage | Lean Command

The Closed Loop fuel control operation will not take place under any of the following conditions:

• | At engine start up.

• | When the fuel injection is increased just after engine start up.

• | When the engine coolant temperature (ECT) sensor is indicating a low coolant temperature.

• | When the engine is operating under a high demand, such as wide open throttle (WOT).

• | At fuel cutoff.

• | When the HO2S 1 is cold (Open Loop operation).

• | When the engine is running at high speeds (higher than about 4000 RPM).