So, I had a #1 cylinder misfire. I changed the coil, no luck. Over the weekend I put a new plug in #1 cylinder, cleaned TB, and cleaned MAF. Misfire issue resolved! Now I had PO420 code come in after about 2 days. It looks like it has something to do with the cats, but not exactly sure what to do abouot it.

Any help would be appreciated

'04 5.4L
68K Miles

 

i usually clear that code to see if it'll come back. the misfire may have destroyed the cats. does it feel a little bit sluggish compared to normal? any loss in fuel mileage?

 

I disconnected the battery cable twice and it would come back after starting a couple of times. I had autozone clear it today when I had it read. I didnt get that code until after I cleaned the TB and MAF and changed the plug. I am planning on changing the rest of them tomorrow

The truck runs great now that that stuff has been done. It seems the fuel mileage has went up just a tad after that also

 

The converters are still covered under 8/80 emissions warranty. Let your dealer worry about it.

 

Is this something I would have to pay a $100 diagnostic fee with or would it vary by dealer? Would it most likely be a cat, or could it be an o2 sensor?

 

Some dealers might try to get one over on you and get you for the diagnostic fee, but Ford pays the dealers for checking and replacing the converters under warranty (they don't pay much, but they do pay).

Tote it to your local dealer and tell them that another shop told you a converter was bad. They should take it from there. Just make sure the check engine light is on and the code is set before bringing it in.

 

The CEL hasn't come back on so far so I will take it in if it does