Hey guys.

I have the sweet P0420 code, and have had it for the past 5 years... ready to do something about it.

Been sweeping through threads & posts for the past 3 hours without an answer to my question (which is why im posting now )

Heres the specs:

04 FX4 f150, 5.4. 195k miles. I already have the back 2 cats cut off and duals out from the muffler. (have had code since before i did any exhaust work)

From what ive read so far, this code is usually a plugged cat on the passenger side, and sometimes can be the 02 sensors.

I plan to take it to the shop sometime again and get the cat checked for being clogged.

My main question is, what type of pre cat do i need to buy from magnaflow if i want to replace both of them? on the magnaflow website they are showing 99176HM and 51176 as being acceptable fits for my truck. im assuming these are "high flow"?

Also, im assuming the passenger side pre cat is the "right front"?

Any help/direction is greatly appreciated. Thanks guys!

 

The angled pre-cat style aren't necessary they are designed to work with the 4 cat system. Cutting the rears out is just a fun little way to make them louder.

Get some #94106 cats with the O2 sensor mounted right after them a few inches ( may or may not need O2 extensions ). That is a good 1 piece per-side replacement and wont hold back volume like the HM ( heavy metal ) series cats may.

 

What about the #91076, they are angled and I don't think its the HM style and is still a high flow. Looking at replacing my front cats with this and deleting my rears, just seems to be the easier route. My O2's won't have to be moved to far and should get a nice sound.


Has anyone installed these Magnaflows with the 04 4 cat style?

 

There is no such thing as Pre cats.
The truck is equipped with two per side for long mandated life.
The after market replacements are often smaller because on a vehicle with a lot of mileage is not expected to last as long so the size and metal used may not be stainless steel in some parts of the system to keep replacement cost down.
The rear sensor only monitors Ox content or 'stored' Oxygen.
If you look at the Ox sensor voltage reading is stays quite stable on a good system.
The computer monitors the switching ratio between the fronts and the rears.
When the rear sensor begins to move voltage excessively and begins to follow the front sensor, the codes are set indicating the cats are no longer functioning at the minimum oxygen storage design level.
Removing one cat removes half the storage capacity of the system causing a shorter life span leaving only one cat each bank to function.
This is why the rear sensor is mounted in the center of the rear cat and not in the pipe just behind it.
Cat flow ratings on a truck is a non performance issue.
If you have a motor making 500 hp and revs to 7000 rpm, maybe Cat flow would make a small difference.
Good luck.