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  #1  
Old April 12th, 2018, 09:06
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How much knock is too much knock?

1998 XJ
4.0I6
Head swap in December. About 6k put on it since.
Recent oil change less than 500 miles ago

Started up the XJ and it seems just a bit too knocky. They always make some noise when they are cold but this sounds like a light diesel. It did go away once the engine was at running temp and no fluids are disappearing. Filmed the knock
https://youtu.be/JwqPox1euWQ

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Old April 12th, 2018, 09:20
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Re: How much knock is too much knock?

Sounds like a lifter. It can go a long, long time that way before failure.

I'd ignore it until it blows. Which may be another 100K miles.
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Old April 12th, 2018, 09:44
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Re: How much knock is too much knock?

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Originally Posted by cal View Post
Sounds like a lifter. It can go a long, long time that way before failure.

I'd ignore it until it blows. Which may be another 100K miles.
How will I know when it goes? How will the engine run as result

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Old April 12th, 2018, 09:47
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Re: How much knock is too much knock?

It would get a lot louder and the engine would start missing.

Or a valve would stick open, a piston would hit it and possibly blow a hole in the side of the block.
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Old April 12th, 2018, 09:49
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Re: How much knock is too much knock?

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Originally Posted by cal View Post
It would get a lot louder and the engine would start missing.

Or a valve would stick open, a piston would hit it and possibly blow a hole in the side of the block.
Okay I was curious because this engine pings and I've had to use premium only since i cant figure out what the problem is. I can see they aren't related now

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Old April 12th, 2018, 10:03
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Re: How much knock is too much knock?

Pinging is generally a problem with it being lean. Have you checked the fuel pressure?
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Old April 12th, 2018, 11:34
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Re: How much knock is too much knock?

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Pinging is generally a problem with it being lean. Have you checked the fuel pressure?
I did however I used a rental tool so not sure if it was accurate or not. I had a thread on my fuel trims a while back but I didn't get much out of it aside from go research fuel trims. Haven't had the time

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Old May 20th, 2018, 12:32
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How much knock is too much knock?

I feel the need to update this thread. I can definitely confirm this is low end knock. Removed my throttle body today for a cleaning and started it to see how it idled after the cleaning and got a better recording after realizing it was louder from below.
This seems too loud even for an xj and I cant help but think it could be related to me having to use premium only since it pings with regular.
https://youtu.be/JZBaFGHtnIQ

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Old May 20th, 2018, 13:14
RCP Phx RCP Phx is offline
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Re: How much knock is too much knock?

I don't know what your expecting! Sounded like a normal 4.0 to me!
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Old May 20th, 2018, 14:49
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Re: How much knock is too much knock?

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I don't know what your expecting! Sounded like a normal 4.0 to me!
The black xj next to it has 300k on it and year old gas in the tank but doesn't knock. Maybe I'm just not used to owning a 4.0 that an average wreckless human owned. Late oil changes, no coolant or air filter changes ect. I dont know the history of the xj I pulled the engine from. I just know all the work i put in it since i dropped it in mine

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Old May 20th, 2018, 15:47
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Re: How much knock is too much knock?

Quote:
Originally Posted by alexgalexg View Post
They always make some noise when they are cold but this sounds like a light diesel. It did go away once the engine was at running temp and no fluids are disappearing.
Rod knock gets worse as the engine warms up.

I really like how you go in-depth while trying to diagnose your vehicle problems. The next step is to buy a mechanics stethoscope and start probing; it's fun!
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Old May 20th, 2018, 15:56
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Re: How much knock is too much knock?

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Rod knock gets worse as the engine warms up.

I really like how you go in-depth while trying to diagnose your vehicle problems. The next step is to buy a mechanics stethoscope and start probing; it's fun!
Will have to add that to my list along with a new fuel pressure gauge. I dont think harbor freight sells a non leaking one!
I will tell you this. When I put the new head on in December I, of course used assembly lube on the rods and rockers. When I started it I couldn't believe how smooth and quiet it ran. Not a knock. Ran like my other xj. But if course it only lasted that one start

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Old May 20th, 2018, 16:04
BALTANAKT BALTANAKT is offline
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Re: How much knock is too much knock?

Does it disappear when you rev the engine?
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  #14  
Old May 20th, 2018, 17:18
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Re: How much knock is too much knock?

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Does it disappear when you rev the engine?
Cant say it does. I haven't tried that exact method but leaving for work in the morning it sounds just as much like a diesel after backing out of my spot in the driveway as it did 2 secs ago before I hit the gas.
Once the engine is on the warmer side it clears up.
No issues with performance or stalling

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Old May 20th, 2018, 17:51
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How much knock is too much knock?

Unless you mean during the actual rev itself. Which I am not sure. If you need this information let me know and I will give it a small tap tomorrow

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