I have a set of Dynatech long tube headers and need to replace the high flow cat that came with them. Started throwing errors after 4 or 5 months and the shop believes it's the cause. Running a 2" exhaust into a SI/DO Super 44 muffler. I see alot about the magnaflow 94106 but looking for some opinions......2004 5.4 BTW

 

What are the exact errors - please post the codes.

That's the cat.

94136 with the O2 bung, 94106 without ...

MGD

 

P0420-Catalyst System Efficiency Below Threshold (Bank 1)
P0430-"The same" (Bank 2)

 

You might have an exhuast leak. I get P0430 in the winter since the poor weld job on my high flows expands.

 

Leak upstream perhaps?

https://www.f150online.com/forums/ex...ml#post4709125

https://www.f150online.com/forums/v8...ode-p0420.html

I don't see both cats failing, unless you did something like running a lot of Seafoam, or cheap octane booster, or are running rich enough to toast the cats, etc.

MGD

 

I've never added any additives but can't say on the running rich part. I'm not sure what would cause that or how I would even check it? I should add that I was only getting an error on the passenger side bank for the longest time. It would trash my O2 sensor after a few hundred miles. I had the shop move my O2 bung back a little farther on that side and quit having that problem, but began getting these new errors in it's place.