Tuned Port Injection Essay Research Paper The — страница 3

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ECM to constantly calculate and update the air/fuel mixture for optimum economy and performance. The sensor itself looks roughly like a spark plug, with anywhere from 1 to 4 wires connected to it. It is always threaded into a fitting located between the exhaust manifold and the catalytic converter. Most sensors have a single wire that carries the signal to the ECM; sometimes this type will have a second wire that acts as a sensor ground. Some are heated sensors that have either three or four wires. In three wire sensors the extra wires are for the sensor heating element, and the heater ground wire. Four wire sensors have an additional wire to ground the sensor. The tip of the sensor usually contains a ceramic/zirconia element that is coated with platinum at the exposed end, and

is covered by a fluted metal sheath. The other end of the sensor usually has either a small metal canister or a plastic sheath that contains ambient air. The tip of the sensor protrudes into the exhaust stream and the difference in the amount of oxygen in the exhaust compared to the amount of oxygen in the ambient air “trapped” in the end of the sensor causes a small (0.10 to 0.90 volts) amount of voltage to be generated. The smaller the oxygen content difference between the exhaust and the ambient air, the lower the voltage generated and vise-versa. Therefore, leaner mixtures generate lower voltages and richer mixtures generate higher voltages. Actually, the sensor acts as a small chemical battery. In operation, the sensor voltage will “swing” from rich to lean and back,

as the ECM constantly monitors the exhaust oxygen content and alters the air/fuel mixture to compensate. The threshold between rich and lean in 0.45 volts; each time the sensor voltage crosses this figure a “crosscount” occurs. Crosscounts are an important figure for advanced engine management troubleshooting. The Throttle Position Sensor (TPS) is a rotary 3-wire potentiometer. It produces a variable voltage that is used by the ECM to determine the position or angle of the throttle blades. The ECM requires this information to determine a number of engine operating parameters, including air/fuel ratio, torque converter lockup, and ignition timing. The TPS is always located on the throttle body assembly, mounted on the throttle shaft opposite of the throttle linkage. The sensor

is grounded through the ECM, which sends a 5-volt reference signal to the TPS. The third wire supplies the variable voltage to the ECM that indicates throttle position. The Vehicle Speed Sensor (VSS) is an often misunderstood and ignored component of the engine management system, but it is definitely an important one. Depending on the application, the VSS can control any one or more of the following: torque converter clutch lockup, cruise control operation, Idle Air Control (IAC) valve position, ignition timing, and shift light activation. There are two primary types of VSS: models with a speedometer cable, and models with an electronic speedometer. On models that use a speedometer cable the VSS is mounted behind the speedometer head in the instrument cluster. The smaller black

end is the pickup, which consists of an infrared Light Emitting Diode (LED) and a photodiode mounted facing each other. In operation a trigger wheel rotates and alternately exposes the LED to the photodiode and hides it. As the photodiode reacts to the light and dark stages, it sends a signal to a buffer unit at the other end of the VSS assembly. The buffer converts the signal into a square wave for the ECM to process. The higher the frequency of the square wave, the faster the speed interpreted by the ECM. On models with an electronic speedometer, the VSS is mounted directly to the transmission, where the speedometer cable connection would normally be. This type of sensor outputs directly to the ECM, which uses the signal both to perform the various calculations listed above as

well as to send the output to the speedometer. Unlike the speedometer mounted VSS the transmission mounted VSS delivers a magnetic pulse similar to a distributor pickup sensor. The information from these sensors is used to calculate the proper pulse width for the injectors and the ECM then fires the injectors for the calculated period. This procedure is repeated continuously in very rapid sequence to maintain the optimum air/fuel ratio. The electronic spark timing sensor and module provide maximum timing advance to improve engine idle and performance. If engine ping is detected by the knock sensor, the timing is automatically retarded to prevent damage from occurring. This is also a continuous process. The Erasable Programmable Read Only Memory (EPROM) chip that is installed in