LS V8 engine rattle @ approx. 900-1000 rpm

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Wabel

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Hello All,
I'm the original owner of a 2004 V8 LS. The engine has a rattle that sounds like its coming from driver side top of engine. This rattle only happens within a narrow range of around 900-1000 rpm. No rattle below or above. It rattles at that rpm when accelerating and decelerating as well as when the car is in park. I have confirmed it is indeed an engine rattle but cannot pinpoint cause. My best guess is it is coming from under the intake manifold or the valve train.

Your help is appreciated.
Wabel
 
All the time or only just after startup? Only when cold, or only when warmed up? Did it just start doing this? Have you tried it with the belt off?
 
Thanks for your quick reply. All the time. Its been at least 6 months and rattles warm or cold. Its a loose semi-metallic rattle that is in the top of the engine. At first I thought it was timing chain related but have been told that the rattle would be there all the time if it was a chain. If the car is in park and you raise the rpm to around 900-1k and hold it there it will rattle until you take your foot off the accelerator. What do you mean by "with belt off"?
 
Take the serpentine (accessory) belt off and run the engine briefly (one minute or less) at 900 to 1K RPM to see if the rattle is still there.
If it isn't, then you are lucky and it is one of the accessory items (or belt tensioner or idler or damper) and will not be too expensive to fix.
If it is still there, then my wild best guess is that one of your cams is moving back and forth (and not just spinning like it is supposed to). If so, that is major.
 
Wabel said:
What do you mean by "with belt off"?
Click to expand...

he means to take the belt(the only belt you can see on the motor) off of the motor and run the engine (for a very short amount of time) if it goes away, then the problem is with one of the accessories mounted to the front of the engine (or possible a tensioner or idler). if the noise remains, then it is likely that it is the motor itself.


EDIT: never mind, walked away to let toe dog out and Joe beat me to it
 
Wabel said:
Hello All,
I'm the original owner of a 2004 V8 LS. The engine has a rattle that sounds like its coming from driver side top of engine. This rattle only happens within a narrow range of around 900-1000 rpm. No rattle below or above. It rattles at that rpm when accelerating and decelerating as well as when the car is in park. I have confirmed it is indeed an engine rattle but cannot pinpoint cause. My best guess is it is coming from under the intake manifold or the valve train.

Your help is appreciated.
Wabel
Click to expand...

As you are the original owner, you should know if the Timing Chain Tensioners have been replaced or not, which given your description of the noise, could be you issue.
 
Thank you all. I will try running without the accessory belt. The car has 80k miles on it and the tensioners have not been replaced. The tensioners are what I first suspected. A couple mechanics told me they do not think it is a chain/tensionor related issue because the car runs smooth and the noise is only at 900-1k rpm. They told me that the rattle/knock from a broken tensioner and loose chain would be constant and engine would sound and run terrible. Is that true? I've considered the CAM moving around as well. Maybe a loose cap? What about CAM phaser or VCT solenoid? I'm also wondering if the rattle is caused by a vibration at that rpm or if the computer is asking the engine to perform a task and what the engine is trying do is causing the noise. It is just so consistent at 900-1k rpm.
 
All2kool said:
As you are the original owner, you should know if the Timing Chain Tensioners have been replaced or not, which given your description of the noise, could be you issue.
Click to expand...

He has a 2nd gen. No one has had to replace the tensioners on a 2nd gen. It's not the chains rattling.

(Yeah, I know there is no way on earth to convince you that any of the 500 improvements for gen II were actually improvements. That said, please point me to any cases that you know of where the 2nd gen V8 timing tensioners failed.)
 
I don't think it is a cam phaser as those usually only make noise right after startup. No, it's not a chain. Apart from the fact that the gen II doesn't have that problem, if it did, it would start as a cold engine rattle that went away as the engine warmed up, and it should be there at low RPMs.
Could you make a recording of the noise?
 
Yes i will make a recording. Another mechanic told me he thought it was coming from under the intake manifold. He said there are pieces of it that can rattle. The car is now at a Ford dealer and they are willing to spend a little time with it at no cost to me, I will try to upload a recording as soon as I get it back.
 
I had a missing bolt on one of the heat shields near the headers (drivers side) that only made a rattle at a very certain and very narrow RPM band, however it was a bit higher up in the band if I remember correctly.
 
I still don’t have the car but I heard from Ford today and in their opinion it's the Cam Phaser. I asked how they came to their conclusion and was told that they disconnected the electrical connection to the VCT Solenoid and the rattle/knock went away. So I have a few questions for you all.

What is the cam phaser and VCT solenoid doing differently at 900-1k RPM that would cause the rattle/knock? Is it at some type of engagement and disengagement point?

How would a bad cam phaser produce rattle/knock? Is it loose?

Could this be a VCT solenoid issue only with it not providing proper oil pressure?

Thank you everybody for your interest and your help.
 
What weight and type of oil have you been using?

The VCT adjusts intake valve timing based on conditions. It is not an on or off thing, it is variable. I think that their test is enough to say that it is likely some issue with that intake cam. I'm not so sure that it absolutely narrows it down to the phaser.
 
5w20 Mobile One full synthetic but my last oil change was a 5w20 Motorcraft full synthetic at a Ford dealership.
 
My 2002 LS V8 used to make noise from the intake manifold around 900 - 1100 rpm when under load, usually when it would kick in overdrive. Made that noise for 8 years until the day I sold it.
 
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