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


imageOpen In New TabZoom/Print



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.


imageOpen In New TabZoom/Print



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


imageOpen In New TabZoom/Print



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).


imageOpen In New TabZoom/Print



10. Remove the left exhaust manifold pipe nuts.


imageOpen In New TabZoom/Print



11. Remove the right exhaust manifold pipe nuts.


imageOpen In New TabZoom/Print



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


imageOpen In New TabZoom/Print



14. If necessary, remove the oxygen sensors.