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Unread 03-31-2006, 09:13 AM   #1
DesertOne
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Knocking Sound ?

I have a 1996 Jeep Cherokee Classic 4.0L, 6cyl which has 157k on it. Lately I have been hearing a knocking sound in the engine. It almost sounds like to me that it is the air/gas mixture not right being right. Not sure, just a guess. I had thought about changing the Knock sensor, but low and behold, I can not find any anywhere. Does the knock sensor sound like the right direction on this?

Thanks for any suggestions....

Ted W
Phoenix, AZ

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Unread 03-31-2006, 09:46 AM   #2
AZ Jeff
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Quote:
Originally Posted by Woosan1
I have a 1996 Jeep Cherokee Classic 4.0L, 6cyl which has 157k on it. Lately I have been hearing a knocking sound in the engine. It almost sounds like to me that it is the air/gas mixture not right being right. Not sure, just a guess. I had thought about changing the Knock sensor, but low and behold, I can not find any anywhere. Does the knock sensor sound like the right direction on this?

Thanks for any suggestions....

Ted W
Phoenix, AZ
Post Renix machines don't have a knock sensor.
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Unread 03-31-2006, 11:41 AM   #3
XJ4oh
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Bad air/fuel mixture is usually a ping kind of noise. Is the knock coming from the top or bottom end of the engine?

Almost every 4.0 I have heard (including mine) knocks and ticks noticably.

Common causes are sticking lifters, and cracked exhaust manifolds. But it can be more serious like a rod knock, but hopefully not.
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Unread 03-31-2006, 02:33 PM   #4
XJ95mlake
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my 4.0L HO does not knock or ping or anything. It's as quite as a church mouse. That is, until i hammer the pedal and get the 4.0 HO roar.... sweet.
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Unread 03-31-2006, 02:52 PM   #5
XJ4oh
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Quote:
Originally Posted by XJ95mlake
my 4.0L HO does not knock or ping or anything. It's as quite as a church mouse. That is, until i hammer the pedal and get the 4.0 HO roar.... sweet.
Your lucky, haha. How many miles are on it?

And yes, the imfamous 4.0 roar is great. It really is the only engine that sounds like it does.
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Unread 04-06-2006, 09:08 AM   #6
92laredo
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if it's coming from the bottom end...check the torque converter bolts. mine did the same knock and 3 of the 4 bolts were almost all the way out. just remove the shield and you'll see the bolts
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Unread 04-06-2006, 10:07 AM   #7
formatt
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possible timing chain slap?... The teeth wear down and it gets sloppy in there. is it kind of intermitant?

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Unread 04-06-2006, 10:20 AM   #8
mjaybird65
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mine has the pinging (not bad, but noticeable), but only on low rpm acceleration. typically in highest gear with slight acceleration - not enough to force a downshift... if this is the result of bad air/fuel mixture, what's the best way to figure out how to even this out? or possible remedies?

thanks
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Unread 04-06-2006, 11:17 AM   #9
XJAce
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Quote:
Originally Posted by mjaybird65
mine has the pinging (not bad, but noticeable), but only on low rpm acceleration. typically in highest gear with slight acceleration - not enough to force a downshift... if this is the result of bad air/fuel mixture, what's the best way to figure out how to even this out? or possible remedies?

thanks
Do you run 87 octane gas? The pinging would go away if you ran mid-grade or even High-test but thats getting pretty expensive now. Even out my way its $2.91 a gallon for high-test. The pinging you hear is called pre-ignition detonation. This happens when the motor has reached normal operating temperature and the combustion temperatures has reached a point were the exhaust that is exiting at the same time the next intake charge is comming in and the exhaust is so hot that it violently ignites the incomming air/fuel mixture(s) and if you comtinue to drive with really heavy pinging your motor is going to be toast. The result of the detonation is a spike in combustion temperatures resulting in fried piston(s) or valves. You can usually tell the signs of detonation even if you can't hear it is when you take the spark plugs out, the center electrode will be melted or even the little hook that lets the spark jump will be melted. Good Luck.......!!
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Unread 04-06-2006, 11:41 AM   #10
gaa
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I have an 89 xj and it started witha knocking sound a few months ago. It only does it when it's warming up though. Once it reached operating temp it sounds normal.
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Unread 04-06-2006, 01:12 PM   #11
mjaybird65
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Quote:
Originally Posted by XJAce
Do you run 87 octane gas? The pinging would go away if you ran mid-grade or even High-test but thats getting pretty expensive now. Even out my way its $2.91 a gallon for high-test. The pinging you hear is called pre-ignition detonation. This happens when the motor has reached normal operating temperature and the combustion temperatures has reached a point were the exhaust that is exiting at the same time the next intake charge is comming in and the exhaust is so hot that it violently ignites the incomming air/fuel mixture(s) and if you comtinue to drive with really heavy pinging your motor is going to be toast. The result of the detonation is a spike in combustion temperatures resulting in fried piston(s) or valves. You can usually tell the signs of detonation even if you can't hear it is when you take the spark plugs out, the center electrode will be melted or even the little hook that lets the spark jump will be melted. Good Luck.......!!
thanks for the info... maybe I'll try to use higher octane until they drop the winter mix and see if that helps. probably time for a tune-up too (at least a check of the plugs)...
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Unread 04-06-2006, 05:40 PM   #12
CJ7-Tim
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Quote:
Originally Posted by mjaybird65
mine has the pinging (not bad, but noticeable), but only on low rpm acceleration.

thanks
2000 and 2001's tend to wear out plugs sooner that older XJ's because of the distibutor-less ignition. New plugs are cheap and help with the gas mileage. Pinging or detonation can also be caused by carbon deposits in the combustion chamber or on the valves. Try a tank or two of gas with some mid price fuel injector cleaner added to it. Sea Foam cleaner works well for me.
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Unread 04-06-2006, 06:03 PM   #13
88XJSport
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Quote:
Originally Posted by XJ4oh
It really is the only engine that sounds like it does.
Man you took the words right out of my mouth. Ive been saying that for years! And its true! I love 4.0's
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Unread 04-06-2006, 06:37 PM   #14
MoochsXJ
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Quote:
Originally Posted by 92laredo
if it's coming from the bottom end...check the torque converter bolts. mine did the same knock and 3 of the 4 bolts were almost all the way out. just remove the shield and you'll see the bolts

I had the same problem but it wasn't the bolts, turned out the flexplate(flywheel) was pretty much shattered and barely hanging in there. She's quieter, but so was I after spending $400 to get it fixed.
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Unread 04-07-2006, 11:15 AM   #15
Matt Gertsch
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Quote:
Originally Posted by XJ95mlake
my 4.0L HO does not knock or ping or anything. It's as quite as a church mouse. That is, until i hammer the pedal and get the 4.0 HO roar.... sweet.
My 93 has no muffler and an open intake. I love the sounds it makes when I get on it. It just sounds mad.
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