The PCM controls fuel injector ON time (pulse width) to meter fuel quantity into intake ports. The PCM receives inputs from engine sensors to compute fuel flow necessary to maintain correct air/fuel ratio throughout engine operating range.
Each cylinder has a solenoid-operated injector that sprays fuel toward each intake valve. Each injector receives battery voltage through an ignition switch circuit. The PCM-controlled ground circuit is used to complete the circuit and energize the injector. Each fuel injector "fires" sequentially (in engine firing order) once per complete cycle.
Injectors consist of solenoid-actuated pintle and needle valve assembly. Amount of fuel delivered to engine is regulated by length of time solenoid is energized. This period is known as pulse width. Atomized spray pattern is obtained by shape of pintle.
Fuel, pressurized by electric fuel pump, flows through fuel damper, fuel filter, injector fuel rail and fuel pressure regulator. Pump is located in fuel tank. Electrical power for fuel pump operation during cranking mode is provided by starter relay, via fuel pump relay and PCM.
Fuel Pump Relay
The PCM turns on fuel pump relay based on inputs from the ignition switch and the ignition coil. During cranking, ignition switch cranking circuit energizes fuel pump relay. After engine starts and key is released to RUN position (engine speed more than 50 RPM), PCM provides fuel pump relay ground.
Fuel Pressure Regulator
Pressure regulator is a sealed unit, divided into 2 chambers (fuel and spring chambers) by a diaphragm. The fuel chamber receives fuel through the inlet side of injector fuel rail. The spring chamber is connected to intake manifold vacuum.
At idle, intake manifold vacuum is high. The diaphragm is pulled back by intake manifold vacuum, and excess fuel is returned to fuel tank. As throttle opens, intake manifold vacuum decreases. The regulator spring overcomes manifold vacuum, increasing fuel pressure.
Fuel Pressure Regulator Control (FPRC) Solenoid
FPRC system includes a solenoid connected to vacuum line of fuel pressure regulator. During hot engine restarts, PCM energizes FPRC. This prevents intake manifold vacuum from going to fuel pressure regulator and increases fuel pressure about 8 psi (.6 kg/cm2 ).
Idle Air Control/By-Pass Air (IAC/BPA) Valve
IAC/BPA is a combination valve that maintains ideal idle speeds under all conditions. BPA portion of valve allows extra air into engine at temperatures less than 140 F (60 C). As engine coolant heats, thermovalve closes and idle speed decreases.
IAC portion of valve is a PCM-controlled solenoid air valve that allows varying amounts of air to by-pass throttle plate to maintain stable idle. When a load causes engine to idle too slowly, PCM increases ON time of solenoid, causing idle speed to increase.
The idle switch detects when throttle is closed and sends signal to PCM, indicating idle conditions are present. Idle switch is integrated with the throttle position sensor. PCM uses this signal to adjust air/fuel ratio and idle speed.
Throttle Position (TP) Sensor
TP sensor uses a potentiometer to monitor throttle plate opening. Its signal to PCM is proportional to opening angle. An idle (on/off) switch is also integrated into TP sensor. TP sensor is mounted on throttle body, at throttle plate shaft.
Sunday, January 25th, 2009 AT 10:20 AM