Mass Airflow Sensor: transmits the ECU (engine control unit) air mass entering the engine.
Oxygen Sensor: monitors the amount of oxygen in the exhaust so the ECU can determine how rich or lean the air/fuel mixture is and make adjustments accordingly.
Throttle Position Sensor: monitors the throttle valve position (which determines how much air goes into the engine), so the ECU can respond quickly to changes, increasing or decreasing the fuel rate as necessary.
Coolant Temperature Sensor: allows the ECU to determine when the engine has reached its proper operating temperature.
Voltage Sensor: monitors the system voltage in the vehicle so the ECU can raise the idle speed if voltage is dropping (indicating a high electrical load).
Manifold Absolute Pressure Sensor: monitors the pressure of the air in the intake manifold. The amount of air being drawn into the engine is a good indication of how much power it is producing. The more air that goes into the engine, the lower the manifold pressure, so this reading is used to gauge how much power is being produced.
Oxygen Sensors are constantly making a comparison between the oxygen inside the exhaust manifold and air outside the engine. If the comparison shows little or no oxygen in the exhaust manifold, a voltage is generated. The output of the sensor is usually between zero and 1.1 volts. All spark combustion engines need the proper air/fuel ratio to operate correctly. Gasoline calls for 14.7 parts of air to one part of fuel.
When the engine has more fuel than needed, all available oxygen is consumed in the cylinder, and gases leaving through the exhaust manifold contain almost no oxygen and are too rich. This will send out a voltage greater than 0.45 volts. If the engine is running lean, all fuel is burned and extra oxygen leaves the cylinder and flows into the exhaust manifold. Now, the O2 sensor voltage goes lower than 0.45 volts. A normal output range is between 0.2 and 0.7 volts.
Fuel InjectorsFuel injectors deliver a fine mist of fuel to the intake valve and combustion chamber. The fuel injector's spray pattern is very critical to the fuel delivery system. Injector nozzles are prone to getting coated with chemical components found in today's fuels. A waxy substance and other chemicals can prevent the injector to properly maintain a consistent spray pattern or atomizing the fuel. Because the injector tips are located over the intake valves, they are subject to a tremendous amount of heat. As the engine is operating, the fuel flowing through the injectors keeps them clean. But, when the engine is shut off, the injectors no longer have the cooling effect of the spraying fuel. This is when chemicals in the fuel begin to form harmful deposits on the injector tips, which distorts the finely atomized spray pattern from the injector.
Vacuum lines and grommets can become stiff, brittle, and leak vacuum. The lines should be checked where they connect to engine and accessories for a snug fit, as well as the grommets around the PCV valve, vacuum hoses around connections to the engine, fuel pressure regulator, cruise control, power brakes, and air conditioning.