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Old 08-22-2013, 06:09 AM   #1
It's a Jeep thing!

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My 4L is running like poo, poo

Well here is how it started... on the way to work, all is normal. On the way home, the engine starting "cutting" out and back firing. It wouldn't hold it's own while going down the road. The more I pushed on the gas the worse it became. So at 1/2 throttle it still was crappy but not as bad. I was able to cripple it home. I put it in neutral the engine seems to run fine. Even when I tac it up 20 3000 rpms. Only difference that I notice is it is idling a tad bit higher. So in a nut shell... under a load it is back firing. I have replaced plugs, wires, cap, rotor, cam sensor. All replaced 1500 miles ago as a tune up.

Thanks in advance. Bob

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Old 08-22-2013, 06:16 AM   #2
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Possible exhaust issue. I changed the muffler and rear exhaust pipe. Man, the crap that fell out of that muffler. Vehicle has a lot more power under load. So exhuast MAY have a restriction. Get underneath the vehicle and with a closed fist bang on the muffler and catalytic converter WHEN COLD. If lots of rattling, your exhaust system needs attention. Just remembered cat is behind transfer case plate. Only the muffler is accessable.

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Old 08-22-2013, 06:41 AM   #3
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It does sound like a partially clogged cat.
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Old 08-22-2013, 06:42 AM   #4
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When I had a similar problem it was a plugged catalytic converter. Changes happened more gradually than what you described though. Still, as panzer-yj said, that area is a good place to start out.
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Old 08-22-2013, 07:04 AM   #5
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I will give that a look see when I get home.

Thanks!!
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Old 08-22-2013, 07:09 AM   #6
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Quote:
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It does sound like a partially clogged cat.
I agree, I had similar issues when my cat clogged. Don't wait to check it out because the pieces of the cat may blow back into the muffler and foul it up.
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Old 08-22-2013, 07:44 AM   #7
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So I'm guessing wacking on it wont tell me anything unless it jars something loose? I'm pretty handy tearing things up.... I guess I should cut the cat out and slide in a spacer tube to see if that was the culprit?
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Old 08-22-2013, 08:03 AM   #8
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the stuff in the cat will usually sounds like marbles in a can when its going bad.. you will then, once removed.. find what looks like white honey comb sections in the tube.

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Old 08-22-2013, 08:11 AM   #9
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Thanks all, does any one know what the OD of a stock exhaust pipe is? and possibly how long the cat is?I would like to pick up a tube before I go home today. I live in a very small town and it's a 24 mile round trip to a parts store.
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Old 08-22-2013, 08:39 AM   #10
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Officially a catalytic converter must be replaced with another catalytic converter. The OD on the muffler is 2.5" both inlet and outlet.
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Old 08-22-2013, 08:53 AM   #11
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Officially a catalytic converter must be replaced with another catalytic converter. The OD on the muffler is 2.5" both inlet and outlet.
LOL!! I know... "Officially" I'm just going to make a test pipe. Thanks for the info!!
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Old 08-22-2013, 09:05 AM   #12
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I'd say its a clogged cat. I started my jeep with open headers, it sounded awesome!
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Old 08-22-2013, 09:14 AM   #13
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So I'm guessing wacking on it wont tell me anything unless it jars something loose? I'm pretty handy tearing things up.... I guess I should cut the cat out and slide in a spacer tube to see if that was the culprit?
When you turn off the jeep you should hear some rattling coming from the cat area
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Old 08-22-2013, 12:08 PM   #14
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When you turn off the jeep you should hear some rattling coming from the cat area
Haven't noticed any rattling, but I haven't been checking for any.
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Old 08-22-2013, 01:08 PM   #15
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The upper two mini-cats (if you have CA emissions) are pretty bulletproof. If you've got something clogged it will likely be in the larger main cat sitting above the T-Case skid. On mine (CA emissions) there are speed-clip flanges just under the two minicats to separate the lower exhaust from the manifold. Save yourself a trip to the store and just open it up there. you can tie the lower exhaust up with bailing wire and take a short trip to see if it runs smoother.
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Old 08-23-2013, 05:55 AM   #16
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Attachment 289195

Attachment 289196

Well, here is what I found last night. Apparently since I was going so slow just trying to move I didn't notice that I had lost all my power to my "power" brakes. Major vacuum leak.
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Old 08-23-2013, 08:57 AM   #17
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Well, here is what I found last night. Apparently since I was going so slow just trying to move I didn't notice that I had lost all my power to my "power" brakes. Major vacuum leak.
Glad you got it figured out!
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Old 08-23-2013, 09:08 AM   #18
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Well there you have it. It's always nice to see success without an overhaul.
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Old 08-23-2013, 10:00 AM   #19
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Yep, was a easy fix for sure, I've never seen a cap come off that elbow in the booster.

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