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Discussion Starter #1 (Edited)
Hi, I have a 2007 Range Rover Supercharged with the 4.2L V8 engine. Engine sounds normal when driving, but if I accelerate at 4000 RPM, the engine sounds like its making a metallic noise like a bicycle chain spinning around a gear. The sound continues if I accelerate above 3000 rpm but goes away below 3000.

To clarify, the metallic sound only occurs initially at around 4000 rpm. Only when it hits that rate does it contine to occur anywhere above 3000. If I never get up to 4000 to begin with, the engine sounds normal. Anyone encounter this before and know what might be cause? I tried uploading a video file but app says extension not supported.
 

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Discussion Starter #3
Thanks ddm2k, after searching the isolator, I found another discussion thread where someone posted a sound emanating from their supercharger. Sounds almost exactly like this


But only starting at 4000rpm.
 

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RPM-induced vs. any speed may be the difference between a cracked (compromised, but not destroyed) and a failed part, respectively. It is not a metal part. This exact part was replaced on my 2012 L322 S/C by the dealer during its time with its first owner.
 

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Discussion Starter #5 (Edited)
I just got a call from the independent LR mechanic. He said it isn't the isolator and says that's an issue more to do with the later 5.0L engines. They believe the spark plugs are worn (car is at 98.7k miles and plugs should be changed at 105k) and there is excess carbon build up. This is causing improper timing. The computer is not able to retard the timing sufficiently at high RPM which is causing the "metallic" pinging sound. It only occurs when I accelerate hard at high RPM. He says it's not really any metal pinging away, but is actually the sound of the detonation.

Sounds like previous owner may not have used premium gas or cleaned/maintained in timely manner. They are recommending replace spark plugs and carbon cleaning service.
 

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It just occurred to me how similar our user names are. LOL!

I do recall how detonation has been described as a "pinging" sound. What's not making sense is: why is the computer not able to retard the timing sufficiently? I am not clear on how carbon buildup can cause detonation. I'd believe it if carbon was fouling plugs, causing misfires (failure to ignite). Documentation online shows that carbon buildup causes hot spots in the cylinder causing pre-ignition... Carbon, as an element, has a higher specific heat than iron, but less than aluminum (yet there are vehicles with aluminum blocks, aluminum heads that run just dandy). In other words, I'm just not buying it.

I'm calling for the expertise from forum members to help explain this one. I would understand if you were presently using too low an octane, and the computer could not retard the timing sufficiently under boost. The same could happen at any speed for a vehicle with high static compression. But using the recommended octane NOW should alleviate that symptom.

I am, however, a proponent of frequent spark plug changes. I have no issue with changing the plugs for the sake of changing them. My model year specifies 105,000 miles or 7 years. My previous vehicle (American domestic) specifically recommended the use of plain copper plugs and replacement intervals of 30k. There were 16 plugs. Eek.
 

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Discussion Starter #7
I think what the mechanic meant was if there's a lot of carbon build up, the buildup can continue to burn and ignite the mixture despite the computers efforts to adjust timing. I also found an article online suggesting similar.

Regardless, they changed out the spark plugs and did 2 separate BG induction cleanings. They checked MAF sensors, updated the ECU, checked oil, etc. Still had pinging at higher RPM and auto logic continued showing computer trying to take out timing when you hear the pinging noise .

So for now, will drive off the tank of gas and put in Premium from Chevron or another name brand gas station and then test again and come back if continues. Previous tank was premium but from Costco and local PX gas station. Will go back if continues.
 

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Discussion Starter #8 (Edited)
Drove off the existing gas and filled with chevron 91 octane.

Detonation still happening at 4000 rpm on flat road and about 3000 up steep grade highway. Only occurs under load. So far we have ruled out spark plugs (replaced with new ones), excess carbon (2 BG induction cleanings), ecm (updated and checked), MAF sensor (checked), and oil (checked).

Does anyone have any ideas on cause? Has anyone had this happen to their car and what was your solution?
 

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Discussion Starter #9
After driving off 3 full tanks of Chevron 91 gas, the knock has gone away. The first tank had about the same amount of knock at same RPMs, then it gradually occurred less with each tank full being driven off. After the induction cleaning and spark plug replacement, it appears any remaining carbon buildup gradually got burned off.
 
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