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Old 07-27-2013, 04:36 AM   #1
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4.2 cat help

Hey guess I have been having a problem with my jeep loading up and stalling. my cat is original and I think its clogged. do you think taking it off and running just a muffler and/or a magnaflow system of some sort? I was also thinking of getting a new header, that will let it breath better.

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Old 07-27-2013, 07:23 AM   #2
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I run a 2 1/2" magnaflo cat and XL muffler. it really completed the other mods and made a big difference in performance. if you even suspect that your cat is getting plugged you should do it. really can't say enough about the results.
as long as your exhaust manifold is good I wouldn't bother with a header, the 4.2 doesn't rev high enough to benefit from one.

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Old 07-27-2013, 07:34 AM   #3
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Ok, I'll look into that once I see if this thing is plugged. I am also having another problem. In park/ neutral my jeep idles at 1100 to 1200 but once I put it in drive it drops to about 700 or 800. I know that cannot be right. if I put it in park and lower it down to 8 or 90o and put it in drive it stalls or I have to keep my foot on the gas
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Old 07-27-2013, 08:50 AM   #4
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Obviously, I'm living in Florida that has no yearly vehicle inspections of any kind so eliminating the cat was a no brainer for me. Last weekend I replaced the muffler with a Flowmaster 40 and I'm very pleased with not only the new 'growel' but the overall performance and power. So far I've actually recorded a 2 MPG increase since the installation! Eliminating the cat is the way to go if you can pass your emissions test.

I can't help you with your RPM issue because my ride is manual as opposed to your automatic beyond saying that mine runs perfectly and I idle at 1000 RPMs.
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Old 07-29-2013, 02:32 PM   #5
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Taking off the cat will do four things:

1.) Reduce exhaust backpressure
2.) Open up higher rpms
3.) Reduce low end torque
4.) It will violate Federal emissions laws that prohibit you from removing Federally mandated pollution control devices.
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Old 07-29-2013, 03:54 PM   #6
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Gotta love #4
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Old 07-29-2013, 03:55 PM   #7
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Someone removed my cat before I bought the jeep. It runs fine, but does have an exhaust smell like a vehicle with no cat. Check the idle tubes on your carb. Google carter idle tubes and there is a ton of info about them. They should be misting fuel and not dripping at an idle.
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Old 07-30-2013, 09:26 AM   #8
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That's what hot stickers are for! Are you supposed to look through the cat and see daylight on the other side? what would happen if you just bashed the insides out with a crow bar? LOL!
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Old 07-30-2013, 12:36 PM   #9
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Do you have the original carter BBD carb? If so the idle tubes are probably clogged.

Easy Fix for Jeep 258 Carter BBD Idle Problem

Easy fix if you're handy. As far as the cat goes it's probably clogged. My 4.2 was running terribly and missing. I replaced the cat and muffler and it went from 25/20 CO emissions (aka not passing emissions) to 8.6/20 and the missing is mostly gone.

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