2007 Explorer Ltd 4.6l code P0420

[rowekmr]

Hello
I just got a 07 Explorer Ltd with 4.6l 3v that had bad missing issues and manifold exhaust leak when I got it. It sounded horrible and drove just as bad. I replaced 3 coils and all 8 plugs so miss is gone and after driving about 40 miles the P0420 code came up (only misfiring codes for about first 200 miles). I reset the CEL and it came back on again. Since the exhaust leak seems to seal itself up after 20-30 sec (don't hear the ticking) should I replace the upstream 02 sensors or all 4 sensors first? I am asking because I was going to get the Walker catalytic convertors for about $290 but local mech said start with the 02 sensors.

The truck only has 127K miles but was thinking maybe previous owner damaged the convertor driving with the bad plugs and coils with a rich fuel setting.

Thanks

 

[Bill MacLeod]

Leaking exhaust manifold can also cause a P0420 code. Fix the leak first.

 

[rowekmr]

I believe the exhaust leak is on the driver side and the bad readings are coming from the passenger side. I was hoping to separate the problems because the exhaust leak can be a costly repair. Ford quoted 17 hours to remove engine so now I am looking for independent shop to replace manifolds with engine in. I will now try to get the exhaust leak fixed and replace 4 O2 sensors I ordered off of Amazon and see if that fixes it.

"Leaking exhaust manifold can also cause a P0420 code. Fix the leak first."

 

[rowekmr]

If not anyone have recommendation for convertors? I found Magnaflow and Walker sell them with Walker cheaper.

 

[Explorer_PL]

When I replaced my 4.6 engine, I installed new Magnaflow convertors at the same time. I paid around 300 exactly 3 years ago. No single code since then.