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Unread 12-16-2006, 02:31 PM   #16
M.P
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Wait A Second!
i am doing a quick hijack here,

I cut my muffler off and im not even using a striaght pipe, it just stops at the Cat.
This is bad for my jeep? if it is, then what is a good exuast that is cheap but adds performance and is LOUD! i want to break windows man!

ok sorry to hijack again!

I had a jarred manifold, cost me 800 to fix and i about died of breathing in fumes in cab.

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Unread 12-16-2006, 02:35 PM   #17
anony91xj
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Quote:
Originally Posted by tangofox007
Could you explain how an exhaust leak causes a lean fuel/air mixture?
The leak is before the O2 sensor. Therefore, the exhaust is escaping before it can be metered by the oxygen sensor, and the sensor is getting a false reading. On OBDII cars, pre-O2 sensor exhaust leaks can trip a P0171 and/or P0172 code for lean conditions. It won't cause drivability issues, and on a pre-OBDII car it probably won't even turn on the CEL. It's really not that big a deal unless you're trying to pass an OBDII emissions test.

A leak after the O2 sensor will have no effect on anything except noise level.

Quote:
Originally Posted by Rescuer265
a cracked manifold can help warp the head.
I'd be interested to hear how that works.
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Unread 12-16-2006, 02:36 PM   #18
anony91xj
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Quote:
Originally Posted by M.P
Wait A Second!
i am doing a quick hijack here,

I cut my muffler off and im not even using a striaght pipe, it just stops at the Cat.
This is bad for my jeep? if it is, then what is a good exuast that is cheap but adds performance and is LOUD! i want to break windows man!

ok sorry to hijack again!

I had a jarred manifold, cost me 800 to fix and i about died of breathing in fumes in cab.
You're doing no harm whatsoever. A cracked Jeep manifold (they all crack in the same spot) really causes no harm either.

The only possibility for harm is if the fumes get into the passenger compartment, and then it's harm to the people inside, not the vehicle itself.
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Unread 12-16-2006, 02:50 PM   #19
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I wasnt kidding about the fumes getting into the cabin in my first post.My uncle had a cracked mani and decided to leave it because it was a big job until he started feeling sick.Long story short it was cause of the fumes he was breathing in and his truck was only 2 years old at the time unlike most Jeeps on here that are getting or if there already not at the 10 year mark.
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Unread 12-16-2006, 02:55 PM   #20
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Quote:
Originally Posted by red96jeep
it's just like when you run an engine without headers at all, in that short moment where the cylinder is at TDC and all valves are closed a little tiny bit of frech air leaks in and then the temp of the hot exhust gases and the little bit of flame left in the cylinder get that extra little boost from the new oxygen. after a while it will cause you to burn a vavle.
edit: this is what i've allways been told so if that is all wrong my bad.
a small crack and open headers are completly different. mine is cracked where all teh pipes meet so i dont see how it would suck in air ..there is pretty much exhaust leaving constantly
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Unread 12-16-2006, 02:56 PM   #21
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Quote:
Originally Posted by M.P
Wait A Second!
i am doing a quick hijack here,

I cut my muffler off and im not even using a striaght pipe, it just stops at the Cat.
This is bad for my jeep? if it is, then what is a good exuast that is cheap but adds performance and is LOUD! i want to break windows man!

ok sorry to hijack again!

I had a jarred manifold, cost me 800 to fix and i about died of breathing in fumes in cab.
you will be fine, just dont do what i did and yank the cat too. when i got my jeep i wanted it lout so i yanked the cat and muffler tossed a cherry bomb in not only did it sound god awful it leand out and my o2 died so i just bought a cat and a new o2
now it runs nice and sounds amazing

also dose some one have a picture of there cracked manifold so i know what to go look for
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Unread 12-16-2006, 03:05 PM   #22
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Quote:
Originally Posted by anony91xj
Quote:
Originally Posted by Rescuer265
a cracked manifold can help warp the head.

I'd be interested to hear how that works.

A friend of mine had a crack/hole in the manifold between the 3 and 4 cylander on his jeep. He then had major issues with the head to the point that it was warped. The stealership tech told him it was because of the exaust hole causing issues just inside the head and it warped. I wouldn't have belived it but I saw the spot when they showed us the head, block and manifold and all of the areas effected were connected to where the hole in the exaust started.

So I was going by what I was told.
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Unread 12-16-2006, 03:56 PM   #23
anony91xj
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Quote:
Originally Posted by Rescuer265
A friend of mine had a crack/hole in the manifold between the 3 and 4 cylander on his jeep. He then had major issues with the head to the point that it was warped. The stealership tech told him it was because of the exaust hole causing issues just inside the head and it warped. I wouldn't have belived it but I saw the spot when they showed us the head, block and manifold and all of the areas effected were connected to where the hole in the exaust started.

So I was going by what I was told.
Uhhh...that's nothing short of a complete load of crap. Head warpage is generally caused by overheating the engine. I've never seen or heard of an exhaust leak anywhere causing a warped head.

Half the 4.0 Jeeps out there, heck probably more than half, have cracked exhaust manifolds that never get fixed. Never seen one with any head problems at all.


Quote:
Originally Posted by xj BMX xj
you will be fine, just dont do what i did and yank the cat too. when i got my jeep i wanted it lout so i yanked the cat and muffler tossed a cherry bomb in not only did it sound god awful it leand out and my o2 died so i just bought a cat and a new o2
now it runs nice and sounds amazing
Removing the cat and muffler will not cause a lean running condition. The A/F ratio is determined by the first (upstream) O2 sensor. Unless you cut the exhaust in front of that, you didn't change crap with the A/F ratio when you removed the cat.

Nor would doing what you did cause the O2 sensor to go bad.
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Unread 12-16-2006, 05:42 PM   #24
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Would any air be able to seep into the engine if the crack is right around where it mounts to the down pipe? That's the only place I've noticed a crack. I've also had it smoke tested and nothing came out anywhere else.
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Unread 12-16-2006, 05:46 PM   #25
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Quote:
Originally Posted by anony91xj
Uhhh...that's nothing short of a complete load of crap. Head warpage is generally caused by overheating the engine. I've never seen or heard of an exhaust leak anywhere causing a warped head.

Half the 4.0 Jeeps out there, heck probably more than half, have cracked exhaust manifolds that never get fixed. Never seen one with any head problems at all.

I am just telling you what i was told and saw.
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Unread 12-16-2006, 05:54 PM   #26
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Quote:
Originally Posted by anony91xj
Removing the cat and muffler will not cause a lean running condition. The A/F ratio is determined by the first (upstream) O2 sensor. Unless you cut the exhaust in front of that, you didn't change crap with the A/F ratio when you removed the cat.

Nor would doing what you did cause the O2 sensor to go bad.

ok then i guess it was a coincdence that the o2 went bad

i still advise not putting a cherry bomb on
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Unread 12-16-2006, 06:06 PM   #27
tangofox007
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Quote:
Originally Posted by anony91xj
The leak is before the O2 sensor. Therefore, the exhaust is escaping before it can be metered by the oxygen sensor, and the sensor is getting a false reading.
The problem is not with the exhaust leaking out, per se. The composition of the "lost exhaust" would not be any different than the exhaust that does reach the oxygen sensor. The problem is that ambient air leaks in and presents an oxygen rich sample to the sensor. In response to the false oxygen rich reading, the system sees what it thinks is a lean mixture and enriches the mixture further. So the affect of an exhaust leak upstream from the oxygen sensor would be an overly rich mixture, not a lean one. That would be consistent with the complaint of reduced fuel efficiency and possibly the "bad cat" as well.
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Unread 12-16-2006, 06:45 PM   #28
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I have a cracked manifold and was wondering if anyone has tryed to use jb weld on it.
I like to do things the lazy way
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Unread 12-16-2006, 08:15 PM   #29
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Quote:
Originally Posted by anony91xj
Uhhh...that's nothing short of a complete load of crap. Head warpage is generally caused by overheating the engine. I've never seen or heard of an exhaust leak anywhere causing a warped head.

ANSWER:I have seen an exhaust leak left alone for long enough to burn up the exhaust valve and causing head failure... Seen it, helped put the new one on.

Half the 4.0 Jeeps out there, heck probably more than half, have cracked exhaust manifolds that never get fixed. Never seen one with any head problems at all.

ANSWER:Half are cracked,, I seriously doubt half, but if you dont think the crack gets no bigger and it will run no leaner and it will not f**k up your exhaust valve and then your head... Thats your business I have see it happen first hand

Removing the cat and muffler will not cause a lean running condition. The A/F ratio is determined by the first (upstream) O2 sensor. Unless you cut the exhaust in front of that, you didn't change crap with the A/F ratio when you removed the cat.
ANSWER: True, but most cracks are in front of the upstream O2 Sensor... So it does change the mix, and runs leaner... Not a bunch like on a carb motor, (and it does that for a different reason... not going into that here) but it does change the A/f ratio and its enough to do damgae....
I never thought by giving the original poster the right info that it would lead to such a lively disscusion.....
Nor would doing what you did cause the O2 sensor to go bad.
I just put the answers in under the statments... seemed easier
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Unread 12-16-2006, 09:07 PM   #30
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I love trying to sort the B.S. out of these threads.

"Some guy told me this",
"But some guy told me that",
"I saw this myself"
"I read on an internet forum that some guys mechanic told him his leaky rear axle seal blew up his air conditioner"
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