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Sluggish performance, hard starting? Could be a worn out or sluggish oxygen sensor. The automotive gasoline engine uses a mixture of air mixed with gasoline to create a combustible mixture. It is the burning of this mixture that operates the engine, and after the combustion process a small amount of oxygen remains in the exhaust.

The oxygen (O2) sensor monitors unburned oxygen in the exhaust, and is part of the fuel management system. The vehicle’s powertrain control module (PCM) uses the information sent by the oxygen sensor to determine if the fuel mixture is rich (too much fuel) or lean (not enough fuel). To provide the best performance, fuel economy and emissions, the PCM has to constantly readjust the fuel mixture while the engine is running. It does this by looking at the signal from the O2 sensor(s), and then increasing or decreasing the on-time (dwell) of the fuel injectors to control fuel delivery.

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