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Old 08-27-2012, 08:28 PM   #1
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My CAT is empty ????

So when my muffler was taken off - we notice the cat is empty.
Could someone have cleaned it out to fool the smoggers. If thats the case would that be why Im running rich and getting bad MPG all O2 have been chnaged. Anyway putting a Magnaflo cat on
any ideas ??


97 2.5 169000 miles

thanks

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Old 08-27-2012, 09:57 PM   #2
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That's an old school trick to run catless but still pass a visual smog...it won't pass the sniffer at all or a scan test without a o2 sim. You should have a cel unless there's a o2 sim installed where the post-cat o2 would be.

Yes the uncorked exhaust could be throwing your tune off making you run a little rich.

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Old 08-27-2012, 10:19 PM   #3
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That's something commonly done where there are visual inspections only, no real emissions tests. If you have a "Cali" emissions setup where the 4 O2 sensors are located before the main cat (before and after the "pre-cats") the computer shouldn't tell a difference, therefore no code. I doubt the lack of back pressure (if any real difference) would cause it to run rich. The 2 upstream O2's should just adjust for it.
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Old 08-27-2012, 10:25 PM   #4
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seems like you have gutted cats.
on some vehicles all the cats do is just restrict the exhaust, but i don't see why anyone would do it on a TJ.
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Old 08-27-2012, 11:04 PM   #5
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Quote:
Originally Posted by kewlkarim
seems like you have gutted cats.
on some vehicles all the cats do is just restrict the exhaust, but i don't see why anyone would do it on a TJ.
When they go bad or the insides get loose, they can make an annoying rattle. If you live where there aren't any real emissions tests or visual only, and you don't have an O2 sensor after the main cat, it's a cheap "fix". Some people consider it a cleaning if they think it's plugged. It's not so much for a power gain.
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Old 08-27-2012, 11:06 PM   #6
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It would be a Combo of Lean & Rich without the Cat in there.

You'd be Lean Down Low, but Rich Up Top.
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Old 08-27-2012, 11:31 PM   #7
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Quote:
Originally Posted by Duramaxxed
It would be a Combo of Lean & Rich without the Cat in there.

You'd be Lean Down Low, but Rich Up Top.
I don't see how in a Cali setup. The upstream O2's control the amount of fuel and they don't care if the main cat is there or not.
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Old 08-28-2012, 04:36 AM   #8
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Quote:
Originally Posted by HarryJeepGuy View Post
I don't see how in a Cali setup. The upstream O2's control the amount of fuel and they don't care if the main cat is there or not.
That's what I would've thought also.
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Old 08-28-2012, 11:43 AM   #9
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It's hard to Explain, but if you put it on a Dyno and got AFR Readings, you would see it.

If you're just Putting around Town, you really wouldn't Notice, but if you went to Pass someone, Pull Out into Traffic, Merge onto Highway...any time that you need to Lay into the Throttle more than usual, you would See the Lean / Rich Condition.

Not Necessarily Dangerous Levels, but enough that you could Experience a Hiccup or 2.
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Old 08-28-2012, 11:47 AM   #10
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Quote:
Originally Posted by Duramaxxed
It's hard to Explain, but if you put it on a Dyno and got AFR Readings, you would see it.
Huh. Evidently it's not enough to throw a code? I could wrap my head around the idea on an engine with a carb, but just don't see the difference in back pressure doing that much. Sounds like a question for Jgorm or someone with tuning experience.
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Old 08-28-2012, 03:02 PM   #11
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Both O2 sensors are used to determine a/f ratio. The PCM looks at the difference in the readings and makes adjustments accordingly.

It is strange your CEL isn't on, the bulb isn't burned out is it?

I like the fact that you are putting a CAT back in. Don't believe the lies about getting more power by gutting/removing it. It's not a dragster
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Old 08-28-2012, 11:43 PM   #12
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Thanks guys- picking up Jeep tomorrow - hi flow cat installed... hope it helps makes things run better


p.scott

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