2007 Explorer code-P0420 Cat below threshold?

[CAPTAINTR1]

I have a 2007 Explorer with the 4.6 liter. 91,000 miles, I just changed the plugs (that was fun...thank goodness for the Lisle tool!), boots, and fuel filter.
Prior to this, the truck had a miss and would stutter at high speeds. The truck runs awesome now, better then when I bought it 5 years ago.
Yesterday, the check engine light came on. I used my scan tool and it read a P0420 code "Catalyst System Efficiency Below Normal Threshold Bank 1".
I cleared the code and today the light came back on, same code.

Any ideas?

 

[Rcflyer330]

Well it can be a couple of things a bank 1 sensor 2 o2 sensor or a bad cat. To check the ot sensor you need to view live data ad watch the o2 sensors. Do a google or youtube search on how to check o2 sensors. The way to test the cat is to get the car warm then use a infrared thermometer to temp the front then the back of the cat wile the engine is at about 2000 rpm the output should be hotter than the input. Ericthecarguy on youtube has some good videos for testing both of thease and possibly fordtechmakuloco

 

[Lamancha]

I had a similar code P0430 Catalyst System Efficiency Below Threshold (Bank 2).

I replaced the cat with a Magnaflor Cat.
http://www.amazon.com/Magnaflow-992...&redirect=true&ref_=oh_aui_detailpage_o02_s00

The code has never appeared again.

You will need to check the H02S sensors, the fuel pressure, check for leaks in the exhaust system.