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Old 10-29-2012, 09:03 PM   #1
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Default 4.0 noise

My 98 Cherokee POS strikes again. It has a nasty sounding knock that started suddenly. I would describe it as a loud, "metallic" sound. It is not in the valvetrain.

I had a guy listen to it; he was the head mechanic at the local Chrysler/Jeep dealer for many years in the 80s and 90s. He said his first thought was a broken piston skirt, but that when that happens, the sound usually gets quieter by pulling the plug wire on the affected cylinder, which this doesn't do. He mentioned the possiblity of a cracked flexplate, but he and his co-workers all thought it sounded like it was coming from the engine, as did a couple mechanics at the Jeep dealer, who also listened to it. Bottom line, everyone who has listened to it says, "Ooh, that doesn't sound good...", but no one feels confident about what's causing it.

I should also mention that it runs the same as it did before the noise started, and it runs well.

I know sounds can travel in metal, and I sure don't expect anyone to be able to diagnose it by my description, but if anyone has any tips to help narrow it down, I'd be grateful. Thanks!
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Old 10-29-2012, 09:12 PM   #2
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does the noise come and go? does it change in relation to RPM? we need more info on the noise.

While it may not sound like its in the head the lifters and cam are down in the block so it could be the usual lifter tick.
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Old 10-29-2012, 09:24 PM   #3
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Quote:
Originally Posted by The_ocho View Post
does the noise come and go?
No.
Quote:
Originally Posted by The_ocho View Post
does it change in relation to RPM?
Changes in frequency, yes, doesn't change much in intensity.
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Old 10-30-2012, 09:42 PM   #4
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I pulled the access cover and did not see any cracks in the flexplate. %$#@!
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Old 10-31-2012, 12:36 AM   #5
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Crum. Probably should pull the oil pan next and see what's there.
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Old 10-31-2012, 06:56 AM   #6
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Quote:
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I pulled the access cover and did not see any cracks in the flexplate. %$#@!
Bolts tight attaching flexplate to torque converter?
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Old 10-31-2012, 11:52 AM   #7
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Bolts tight attaching flexplate to torque converter?
Yes, unfortunately.
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