[Dunlosky50]

Hello, like the title states I have an 06 mountaineer with the 4.0 v6 195k miles that I just bought and its throwing codes for 300,302 and 420 I know they’re random misfire, cylinder 2 misfire and cat below threshold but my question is, are there any common parts that would be responsible for the three codes? i.e fouled plug, old wires, bad ign coil, dirty fuel filter, head gasket?? What’s my next move here? It stutters anytime you’re cruising at a steady speed and hit an incline of just about any degree. Have to let off gas and re-apply for it to bump up to 2800ish rpms and begin gaining speed. At idle it doesn’t seem to miss a beat.

 

[CatSkinner]

I'd start looking for a vacuum leak first.

 

[Dunlosky50]

I'd start looking for a vacuum leak first.

I ran a cheap smoke test and I couldn’t see any leaks,

 

[CatSkinner]

P0420 is saying the cat isn't performing, the misfire could be indicative of improper burn which would contaminate and foul the cat. Or the cat could be failing, creating back pressure resulting in the misfires. Confirming all of your vacuum tubes are intact is a cheaper check than changing the cat to see if the P0420 goes away. A bad injector can also do this, particularly if it's leaking fuel on its off cycle. Also a bad plug/coil. If all of the hoses seem intact, inspect the plugs, especially #3.