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  #1  
Old March 5th, 2009, 19:14
latenights latenights is offline
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exhaust leak on exhaust manifold

Just a quick question after trying to search for it. theres a pretty big crack in the exhaust manifold where it all collects at the end which is pretty common from what i've heard. thats not my problem, i already have new ones waiting to go in when the weather gets warmer. But i am gettin 11-12 MPG city on a stock height 96 XJ 4.0 with 30" BFG A/T. Im just wondering if that could be causing an o2 sensor to be off and making my gas mileage suck. I'm not concerned about this, im just wondering.
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Old March 5th, 2009, 19:16
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tbburg tbburg is offline
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Re: exhaust leak on exhaust manifold

Yep. That can cause it!
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  #3  
Old March 5th, 2009, 19:21
latenights latenights is offline
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Re: exhaust leak on exhaust manifold

Ok, thanks. I figured that's what it was but since most people on here are a lot smarted then I am I'd figure I'd ask. I got some new stainless ones with the expansion chambers for $100 at a swap meet so hopefully they'll be going in this weekend.
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Old March 5th, 2009, 21:18
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hubs97xj hubs97xj is offline
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Re: exhaust leak on exhaust manifold

Check your motor mounts and the transmission mount- that is supposed to be one of the contributing factors to cracked manifolds- even my APN header has a little warning on the install sheet that worn mounts likely caused the stock piece to fail, and would wreck the header as well.
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Old March 5th, 2009, 21:49
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winterbeater winterbeater is offline
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Re: exhaust leak on exhaust manifold

Consider adding a stainless flexible joint into the system. Summit sells em. I don't see how those built in expansion pieces will help with the cracking thing.
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Old March 6th, 2009, 04:46
latenights latenights is offline
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Re: exhaust leak on exhaust manifold

ok ill check the mounts. i wasn't sure how they were supposed to help either since there not even on the same tube as where it cracks but i just got it anyway
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Old March 6th, 2009, 07:58
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hubs97xj hubs97xj is offline
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Re: exhaust leak on exhaust manifold

Engine/tranny move around too much on worn mounts, the collector starts cracking as it can't move with the engine, exhaust escapes before the O2 sensor through the cracks, sensor sees a lean mixture, tells the PCM to dump more fuel in, tanking your mileage. That seems to be the prevailing theory- one thing leads to another. Not sure on the bellows, but if you can fix the root cause, it should be fine, even if they don't necessarily help.
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