I have had a loss of power recently and the dealer told me it is my cats. I dont want to pay the outrageous amount for factory cats so i would like to know what my options are. Through search i have found that the magnaflow is the most common aftermarket cat. My truck is a 2004 5.4 so it has the 4 cat design. My questions are:

1. Is it usually the pre cats that clog or the rear larger ones or no way of telling?
2.If its the rear can i just replace them with the magnaflows?
3. If I remove all 4 and replace with magnaflows how is the sound going to be affected.

I have the factory exhaust now with the muffler removed and a pipe welded in place. I like the sound how it is now so I dont want it to be too loud with the magnaflows. Thanks for any help guys.

 

It's going to be 40% louder. I wanted mine louder so that's why i did them. The truck gained a hair more power and a few tenths of mileage, but nothing to write home about. It's gonna be loud, maybe you should through a muffler on there if you do them.

 

i am about to put on magnaflow 94103 i will let you know how they sound. but i have a question for you when you had loss of power did you also lose your sound? I have a 06 5.4 with true dual flowmasters, all of a sudden driving home i lost power and sound i mean i sound like stock exhaust, thus leading me to think my cats are clogged/collapsed. thanks!

 

It is usually the front converters that clog, which is the main catalyst, which is what clogs and fails. Before you replace you should have your engine fully tested and inspected for any rich running condition because that is the only reason catalytic converters can fail, which in that case, your new cats will fail overtime too.

Put 2 Magnaflow part # 94306 cats inplace of the current cats, 1 cat per bank, with the O2s relocated after these new cats in the pipe, not their body.

 

I havent really noticed any difference in sound. Truck just bogs down and has no power.

I pretty sure the motor is running fine. I have Troyer custom tunes so it shouldnt be rich. Im not positive though.

 

Any check engine light? I would disconnect the exhaust at the manifolds and drive it (away from cops lol) and see what kind of power it has then. Sounds more to me like fuel pressure

 

I have had a long headache over this issue actually. I have personally changed the fuel filter, plugs, and COPs with no help. I took it to two dealers who both told me it was the cam phasers causing the timing to be off. I just had those replaced and the dealer called me today and said the knocking is gone but still no power and they think its clogged cats. I have had no check engine light at all. Im hoping this is the issue.

 

^ That is crazy man.

 

Well I would still want them to check fuel pressure for sure. Again if you disconnect the exhaust at the manifold if it runs fine then yes its cats. I have a hard time believe it is though.