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Q: Misfire but when get up to 60 to 70 miles and hour, it runs smooth

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Vehicle inspection report. Co gpm is 21p3110 should be 15.000. Check Engine Light is on. PO300 Random /Multiple Cylinder Misfire Detected.

My car has 172000 miles.
My car has a manual transmission.

A: Hi there. When I get these readings during ...

Hi there. When I get these readings during an emissions test I usually start by checking the fuel pressure. A lean running condition from a weak fuel pump will cause this. If the fuel pump is fine, then I install a scan tool and monitor the sensor readings as a bad oxygen sensor or air flow meter will also cause this. It can also occur from a failure in the catalytic converter. If you need to have this misfire and emissions problem checked, consider YourMechanic, as a certified technician can come to your home or office to diagnose why the engine is misfiring.

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