Hello -
I got a ranger from someone it had been sitting in a field for about a year. Long story short after changing plugs and wires that had been chewed through, clearing water from washing the engine out of the spark plug wells - all that made me drive it for about 20 miles or so with multiple missfires but thought it was bad gas. Got that all resolved and it idles well and drives well 80% of the time. Intermittently, once it warms up it will totally lose all power and barely accelerate unless you really lay into it. So far as I can see I am getting p420 code. Any thoughts? Thank you.

 

The catalyst code could be an indicator that the cat is clogged. A clogged exhaust will cause all kinds of driveability issues.

Considering it has been sitting for a year or so, it's entirely possible someone made that their "home"

 

I thought so too, but why would it be running okay cold?

 

When your engine is cold, it runs in "open loop", meaning it does not receive feedback from most of your sensors except the bare minimum needed to keep the vehicle running. Open loop more or less runs the vehicle off a pre-set table/tune and will ignore sensor inputs while operating in this manner. It's similar to a boot sequence on a computer, until it reaches the point where its accepting feedback from the user, it just does its thing until it is ready.

Once it gets warm/up to operating temp, it will then switch to "closed loop" where it then takes information from all the sensors in the truck when commanded. Things like o2 readiness, emissions sensors, etc all feedback information to the ECU on how to run as best as those conditions will allow. While I't not saying that a clogged cat is your issue, it could be a potential issue. It could also just be a bad sensor, or a worn out cat/con