Misfire at idle once warmed up and code 420

Good morning,

420 is bank 1 catalytic converter is no good. It is no longer processing the gases from the engine. It has to be replaced.

https://www.2carpros.com/articles/catalytic-converter-replacement

As far as the misfire, I would check the fuel pressure and make sure the pressure is correct. Low pressure is common for misfire and 300 codes.

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

Fuel Pressure (Key ON, Engine OFF) .................... 385-425 kPa (55-62 psi)

Roy

Catalytic Converter Replacement

Removal Procedure

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1. Raise and suitably support the vehicle.
2. If equipped, unclip the oxygen sensor connection from the floor reinforcement.
3. Disconnect the oxygen sensor electrical connector.

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4. Remove the oxygen sensor clips from the frame.
5. Disconnect the connector position assurance (CPA) retainers.
6. Disconnect the oxygen sensor electrical connectors.

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7. Unclip the oxygen sensors electrical connectors from the following:
- Hose clip
- Transmission crossmember
8. Disconnect the CPA retainers.
9. Disconnect the oxygen sensor electrical connectors (1, 2).

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10. Remove the left exhaust manifold pipe nuts.

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11. Remove the right exhaust manifold pipe nuts.

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12. Remove the exhaust muffler nuts.
13. Remove the catalytic converter.

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14. If necessary, remove the oxygen sensors.