Knocking on heaven's door - Jeep Wrangler Forum

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Old 01-12-2014, 09:39 PM   #1
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Knocking on heaven's door

hey guys and girls,

My 2008 Jk started making this knocking/engine rattle (like metal balls in a tin can) only when accelerating. The thing drives fine by the way and no notice in loss of power. I seems like it started when i added a quart of oil due to it being a quart low.. (changed oil 2000 miles ago at the time) i checked the dip stick and it seems to be right at the full mark. Any ideas? i have not yet pin pointed the area on where the noise is coming from.

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Old 01-12-2014, 10:33 PM   #2
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Bad gas ? Sound like spark knock. Also check your exhaust heat shield welds. They tend to pop and rattle.

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Old 01-12-2014, 11:08 PM   #3
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My old car made a noise that sounds exactly like what you described and it turned out to be a loose motor mount.
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Old 01-13-2014, 01:16 AM   #4
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God there are so many possibilities to this sound.
1st off, you need to have someone rev the motor while you listen under the hood.
then start narrowing down the sound.

Other things to think about when diagnosing your own issue, tendencies.
Is it only when there is a load on the motor? (not in neutral in the driveway)
Is it only when I really rev the motor. etc.
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Old 01-13-2014, 09:26 AM   #5
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I know back in the day water pumps sounded like that when they were starting to go. Don't know if the new ones still do that though.
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Old 01-13-2014, 08:59 PM   #6
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Thanks Guys! i will check to see if the plugs are at the proper gage, i will try do that this weekend and let you know. Im hoping it is just a loose heat shield. whats the best way to check the motor mounts? And i had it in park and rev'd it up and didn't notice anything out of the norm. last but not least i will take a look into the water pump! thanks again guys for all the input!
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Old 01-14-2014, 05:40 AM   #7
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Don't forget to post the solution in here for future searchers of this forum. (And also I'm curious if water pump bearings still do that. )
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Old 01-21-2014, 11:41 AM   #8
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Thanks again guys! I took out the plugs on Saturday and they all were around .035 to .040 so I gapped them to .050 and the sound is still here. I rev'd up the engine in park and didn't hear anything out of the norm. But this morning I started up and the idle was very ruff and I thought it was about to stall out. I started driving and it warmed up and no more rough idle. but I noticed this past weekend the metal ball in a tin can noise only occurs when the JK is fully warmed up! im starting to think a vacuum leak?? anyone else have an idea??
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Old 01-21-2014, 12:09 PM   #9
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Symptoms sound similar to what happens when the core separates in a catalytic converter.
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Old 01-21-2014, 12:40 PM   #10
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Keep your eyes on that Dip Stick !!! 3.8L engines use oil.....some use LOTS !!
(OK, not ALLLLL 3.8L engines...)
If this is a New to you used Jeep the PO may have run it out of oil and the Rod bearings are hammered....So they will talk at high engine RPM's....

Good Luck ! "BH"
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Old 01-21-2014, 12:48 PM   #11
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I added a quart 2000 miles ago, I use mobile 1 synthetic 5w-30. I just checked it Saturday and its low and will be added some oil soon! and I will look into the catalytic converter some more! thanks guys!
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Old 01-23-2014, 12:04 PM   #12
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My '99 TJ had a similar noise... for the few months until the engine seized up . Though it had about 174k miles on it when it did go.

I was already planning on replacing it, so I wasn't about to spend a lot of money on a major repair.

The noise seemed a lot worse under acceleration. Not sure what the actual cause was, but something was definitely rattling in the engine. I had read about cracked intake manifolds - things like that - but could have been anything. Cracked piston, something internal.

Moral of the story... don't let it go too long if it persists!

Sold it to the tow truck driver, and picked up my new JKUS 2 days later.
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Old 01-23-2014, 02:11 PM   #13
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Quote:
Originally Posted by mickdundee View Post
Thanks Guys! i will check to see if the plugs are at the proper gage, i will try do that this weekend and let you know. Im hoping it is just a loose heat shield. whats the best way to check the motor mounts? And i had it in park and rev'd it up and didn't notice anything out of the norm. last but not least i will take a look into the water pump! thanks again guys for all the input!
If your plugs are older than 50k miles, it's time to replace them. In this regard, the manual is totally off base. The plugs will not make it to 100k.
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Old 01-23-2014, 02:53 PM   #14
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Your flywheel may be coming apart. My cousin's LJ does the same thing. It ended up being a bad flywheel
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Old 02-04-2014, 07:21 PM   #15
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Thanks again guys! the plugs are fairly new (last year of march) and i put some Lucas deep fuel cleaner and filled up with mid grade petrol and it seemed to do the trick! hopefully it isn't anything else and that it just masked the noise.
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Old 02-04-2014, 07:27 PM   #16
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So it was engine ping from cheap gas. I guess I should really start with the basics when someone has a problem. lol Glad you figured it out.

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