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Weird Exhaust Noise

Old 04-22-2019, 01:16 PM
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Default Weird Exhaust Noise

I took my 1990 XJ to get inspected today and it failed. Itís never failed before. They told me that there was a hole in the exhaust where it meets the manifold, and a hole in the firewall. I was driving back from the shop when it sounded like something dropped down or popped, and my engine started making sounds like a dirt bike or lawn mower idling, and I got hit with a terrible smell. I pulled over to check it out and couldnít see anything out of place. I drove back to my school, where I live, and parked it in the lot. Not sure if this is something I can fix myself or not
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Old 04-22-2019, 01:33 PM
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It sounds like something had a hole that got larger. Are you able to crawl underneath it and maybe snag some pictures? That would help a lot. As far as repairing it yourself, are you mechanically inclined at all / do you own tools, jack & stands?
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Old 04-22-2019, 02:58 PM
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I think it may be the exhaust flange gasket, or at least thatís the advice Iíve been given
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Old 04-22-2019, 02:59 PM
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Originally Posted by Red1992XJ View Post
It sounds like something had a hole that got larger. Are you able to crawl underneath it and maybe snag some pictures? That would help a lot. As far as repairing it yourself, are you mechanically inclined at all / do you own tools, jack & stands?
ill crawl under tomorrow, itís pouring rain today. And I can usually do simple jobs myself or with the help of my brother. I have jack stands and such available at home
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Old 04-23-2019, 11:26 AM
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This is the gasket just behind the crossmember, and I think itís clearly in need of a replacement
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Old 04-23-2019, 02:43 PM
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Hmmm.. the exhaust is rusty.. but most older exhaust pipes are. I'd check around the pipe where it comes off the engine (exhaust manifold) and see if you can see any cracking.

When that sucker is COLD, grab a hold of it and see if you can move it and see where 2 parts aren't moving "together" if you know what I mean...
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Old 04-23-2019, 03:35 PM
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Are these pieces supposed to be attached or should they come off?
Originally Posted by PatHenry View Post
Hmmm.. the exhaust is rusty.. but most older exhaust pipes are. I'd check around the pipe where it comes off the engine (exhaust manifold) and see if you can see any cracking.

When that sucker is COLD, grab a hold of it and see if you can move it and see where 2 parts aren't moving "together" if you know what I mean...
its not so rusty up near the manifold. I just took off the bolts in the picture, which were a nightmare.
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Old 04-23-2019, 03:51 PM
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It looks like the pipes were cut and welded 2x, once behind the shiny pipe to the far left in the picture, and then once behind the flange. Interesting that they'd have a clamp there though...

Since you have it off, replace the gasket.. but you really need to look at the manifold itself. The shop indicated that there was a crack in the manifold (which is incredibly common for the Jeep 4.0L), so you need to at least strongly consider that they're correct and check it. Typically the pipes crack where they join together (the Y sections). It may be hard to get a good look at it, but you need to be sure.
An exhaust manifold replacement isn't terribly difficult, but it's a fair amount of work. If you get the manifold off, it may be possible to just weld the crack (especially if you need a short term fix).

Certainly you can replace the gasket, put it back together and fire it up and see if the sound is better.
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Old 04-23-2019, 04:11 PM
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Originally Posted by PatHenry View Post
It looks like the pipes were cut and welded 2x, once behind the shiny pipe to the far left in the picture, and then once behind the flange. Interesting that they'd have a clamp there though...

Since you have it off, replace the gasket.. but you really need to look at the manifold itself. The shop indicated that there was a crack in the manifold (which is incredibly common for the Jeep 4.0L), so you need to at least strongly consider that they're correct and check it. Typically the pipes crack where they join together (the Y sections). It may be hard to get a good look at it, but you need to be sure.
An exhaust manifold replacement isn't terribly difficult, but it's a fair amount of work. If you get the manifold off, it may be possible to just weld the crack (especially if you need a short term fix).

Certainly you can replace the gasket, put it back together and fire it up and see if the sound is better.
i am probably gonna replace the manifold completely because itís old anyway but I figured it out. When I was driving, the #6 spark plug wasnít tight enough and popped out. I was following the noise to the engine bay and felt the air shooting at my face. Engine runs normally again. But since I took apart the gasket Iím gonna replace it anyway
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