I got some ???'s on my 87 4.0L performance issues - JeepForum.com
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Unread 01-13-2005, 04:14 PM   #1
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I got some ???'s on my 87 4.0L performance issues

my 87 XJ 4.0L auto trans has 192,xxx miles on it right now, i have finished replacing the plugs, wires, cap, and rotor. soon will replace the accessory belt.

my question is, the header is cracked, cant really tell where it is cracked at. it just smokes at idle when i blip the throttle, can a cracked header really affect the engine perfomrance dramatically?

how do i find the timing mark? i have a timing light and i cant really figure out how to find the timing. i dont have a manual at all.

the timing chain, i have no clue when it was last replaced. I know chains and belts are different, belt can flex and stretch easier than a chain. Is it really necessary to replace the chain? how do i tell if its still good?


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Unread 01-16-2005, 07:32 PM   #2
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I've got an '88 and it had a cracked header so I bought one off of ebay for $225 or so and I just put it on and I noticed a large gain in horspower and mainly torque. But if you haven't done something like that before it's a pain to do the first time, it was my first and it took me a whole weekend to do what should have taken an afternoon.
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Unread 01-17-2005, 01:23 AM   #3
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I really don't think your timing is the big factor. I'm not definate, but i think the ability to set the timing on 4.0's stopped around 86. Looking in my Chilton's and Haynes manuals anything after 86 was computer adjusted automatically. As far as the condition of your timing cain and gears could possibly depend on the way the XJ was driven and maintained. I know people who have gotten over 200,000 miles on original equipment and still going.
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Unread 01-22-2005, 01:57 PM   #4
Matt Gertsch
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1999 XJ Cherokee 
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All exhaust manifolds on the 4.0 l will crack sooner or later. Rather than an OEM replacement, you might want to spend the extra cash for a good header. I bought a Gibson stainless header and it made a huge improvement in performance and gas mileage. The Banks header looks nice, but they hadn't brought them to market yet when I bought mine.
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