2003 Pontiac Grand Prix SE 3.1....has no power
have replaced EGR Valve...Down Stream O2 Sensor...Spark Plugs...Exhaust Header Gasket....and now has less power then before...engine runs
The upstream 02 is the sensor that helps control fuel ratio, downstream is just a monitor of catalytic converter efficiency. Have it read for codes, even if the check engine light is NOT on the computer will have stored information and codes. Discount auto stores will read codes for no fee. write them down.
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