brad.fx4

I cut out the 2 rear cats and installed 3" pipe with flomaster exhaust. no codes. sounds fantastic.

kozal01

iTrader: (2)

Mine only has 2 cats stock. I wonder why? Everyone tells me I should have 4 but no one can explain why I only have two.

otto457

05-06 is when they switched from the 4 to 2 cat system. Just depends on build date/factory on when everything got switched over.

kozal01

iTrader: (2)

Ah, excellent! Not like it matters much, but Ive always been curious. Thanks!

Kman66

The 1st Heated O2 sensor in the exhaust system sits between the exhaust manifold and the 1st catalytic converter on both sides. It monitors the oxygen levels in the exhaust by comparing it to a reference oxygen level in normal air. The signals from these sensors are used by the PCM to control fuel injectors , timing, etc. to aid in maintaining an efficiently running engine. The 2nd sensor in the exhaust system is a Catalyst Monitor Sensor and sits after the 1st catalytic convter (sometimes it threads into the converter). It compares its readings to the 1st set of O2 sensors to test the efficiency of the converter. The 2nd converter on these trucks are not monitored. The only thing that may go wrong with removing the rear set is that the truck may no longer pass California SMOG tests. I may soon be testing this theory myself on my 05 5.4L FX4 SCrew.

bennutts

This is something I definitely plan on doing just as soon as I can find someone who can do the welding for me. No shops in my area will touch the cats. I even tried reasoning with one shop but they told me it was illegal.

gone postal

That's because it is illegal.

Reasoning with the shop is going to accomplish nothing, as they'd rather lose one customer than lose their business.

bennutts

I completely understand. Their point of view. I just don't understand why it's illegal to cut the rear ones off especially if Ford went to 2 cats in 06.

gone postal

Because it's a federal offense to alter the factory emissions system of any vehicle. If the facory put it there, it's supposed to remain there.

Many states have lax inspections and it won't get caught, but if it was my business I wouldn't take the chance either.

04_lariat_4x4

it helps if you know the shop atleast a little before you ask to cut the cats out. i've been to the same shop a few times working on my exhaust so they know me. i asked about removing the rear two cats when i took it in to get duals last time and the guy said he'd get back with me on it. when i came back and picked it up he said he could cut them out for me whenever i wanted but i never got around to it.