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Old 09-18-2011, 03:38 PM
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4.7 Main Cat

I was wondering if anybody else who has the 4.7 (standard or HO model) is missing the main cat in their setup. I only have the 2 mini cat's and from my understanding if you remove the "main" one you will get codes. I don't see any extra wires underneath or anything else that would show that somebody removed it and just welded a pipe in its place...... Does anybody know if they made certain models without them?
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Old 09-19-2011, 09:53 AM
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Re: 4.7 Main Cat

From my understanding there were 2 exhaust setups for the WJ's:

1. Federal emissions compliant. These had one main cat after the Y pipe with a before and after O2 sensor.

2. California emisions compliant. This setup has a pre-cat on each side of the Y pipe with a before and after O2 sensor on each side. Then there is a main cat after the y pipe with no sensors around it.

I would be willing to bet that a previous owner cut out the main cat and just put in straight pipe. This will not throw a code since the main cat has no O2 sensors on it. It is also probably illegal, but if they were getting away with that I'm guessing your area doesn't do emissions testing.
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Old 09-19-2011, 09:57 AM
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Re: 4.7 Main Cat

04's did not have the main CAT only the 2 precats.
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Old 09-19-2011, 02:55 PM
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Re: 4.7 Main Cat

Quote:
Originally Posted by scjeep4.7HO View Post
04's did not have the main CAT only the 2 precats.
Hmm, good to know. I wonder why they did that? Any problem removing the main cat on my 2001 and just putting in straight pipe? Would there be any performance differences or gains or should I just leave it alone?
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Old 09-19-2011, 02:56 PM
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Re: 4.7 Main Cat

It obviously is not emissions legal. But there will be no codes by removing the 3rd cat.
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Old 10-06-2011, 01:25 AM
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Re: 4.7 Main Cat

You can remove the third or "main" cat on a WJ that came from the factory with two precats and a third main cat without tripping any check engine codes.

DC even will sell you an OEM straight pipe, DC part #52080379-AA MSRP $82.70, that came on all '04 WJ editions. DC sold these '04's with larger "precats" and no "main" cat.

This pipe will look OEM because it is OEM. You will gain a couple of HP, (barely noticable), but the main reason for doing this is the noticable increase in gas milage. Less backpressure in the exhaust system will allow your engine to breath easier giving you slightly better mileage.
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