Yet another N62 engine knocks like a diesel - E53 X5 4.8is

[danny_acs]

Hello everyone! I've searched the internet and various forums for weeks now, so I am not posting without doing my proper research. I haven't seen anything out there that is analogous to my issue, so excuse me if I have missed something. I've literally spent weeks searching and reading, but no result. Here is the issue along with a video clip, I do hope that someone else has experienced this or has an idea and might be able to help.

My X5's engine has developed an intermittent (i.e. not constant) knocking sound only when stationary in Drive (D). This is when the engine as under a small load in Drive, and the RPM's drop slightly below idle speed. The knocking sounds a bit like a diesel, goes louder as the RPM's drop a bit further (as the AC compressor kicks in or I turn the steering wheel), and completely disappears in Neurtal or when the car starts moving. Almost as if the timing goes out intermittently. It doesn't happen when the engine is cold, only after it warms up to the normal operating temperature. Here is a video/sound clip as the car is in Drive with the handbrake on:



About my X5:
It's a 2006 E53 X5 4.8is at 139,000 miles. I always put Shell V Power and change the oil annually. Very recently I've done a full engine overhaul 2000 miles, 2 months ago, The following was replaced - chains, guides, valve stem seals, bearings, coolant transfer pipe, all sensors, all gaskets, all seals, all fluids, 5W40 oil etc. Pretty much a brand new engine and a lot of work done at a great cost. I am gutted that this problem has occurred now after all this preventative work was carried out. The cam shafts, lifters and piston walls were in good condition - pretty much everything was checked while the engine was out!

Before I go back to the garage that did the work, I want to find out if any one has had a similar issue and has found the root cause. I don't want to start doing any work again before I inform myself about all the possibilities.

I've used an automotive stethoscope to check where the sound might be coming from. I doesn't seem to be the water pump, nether the alternator. I do hear the knocking when I touch on the bolts of the valve cover around cylinder 8. From what i've read so far, it doesn't sound like a lifter which is constant and stays with the RPMs?

One thing I haven't checked is the power steering pump, but I don't think i'll hear anything there as the noise in the stethoscope is the loudest on the valve cover bolts around cylinder 8... That worries me a lot..

So, over to the experts... and fingers crossed it is something simple and easy! Thank you!

[EODguy]

Have you read your codes? If you have... What did they show?

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[danny_acs]

Thanks for coming back. I forgot to mention that no fault codes show up..

I was reading somewhere else that somebody had a similar noise and it was all fixed by changing the gas/petrol tank cap. Apparently incorrect pressure might cause issues with the fuel supply etc. I did get the EML light on the dash a few months ago with an evap error. Changed the seal on the cap and have not had the error since..

[andrewwynn]

When chains were replaced, were the tensioners replaced with OEM grade? It sounds a little like loose chains.

Oil pressure drops at low RPM, tensioner gets fed from oil pressure.

Are you using the BMW recommend oil viscosity and are you at "full" level ?

Does the sound happen at cold start and more specifically, does it happen at first then fades away as oil pressure builds?, That's a strong sign it's chain tensioners.

Even if tensioners are the cause it cold be the oil pump not making enough pressure at low RPM. Not sure if you can read the pressure live from a sensor I don't recall seeing the monitor in my foxwell.

[danny_acs]

Andrew - these are good points.

There was a similar sound before changing the chains, but now it's somewhat different.

I am using Motul 5W40 instead of the recommended 5W30 due to the crank wear being at the upped end of the tolerances. Level is 3/4 between min and max.

It does not happen at a cold start, probably not even at a warm start (after sitting for an hour or two). Only after the engine reaches normal temp.

Good point about the oil pump. When the engine was out, the pump was inspected and there ware no reported issues with it. It's actually quite a big unit this thing.

For these reasons I'm more inclined to think it could be a Valvetronic or air intake issue...?

[andrewwynn]

Chain noise would come from there very front of the engine and can be ruled out with stethoscope.

I had a friend with a loud knock sounded exactly like rod bearing, turned out to be a loose spark plug!

[Purplefade]

Spit balling here but what about the anti knock sensor? Maybe its not pulling timing at lower rpm?

[danny_acs]

Originally Posted by andrewwynn

Chain noise would come from there very front of the engine and can be ruled out with stethoscope.

I had a friend with a loud knock sounded exactly like rod bearing, turned out to be a loose spark plug!

It's coming towards the back of the engine, left bank around cylinder 7 actually, not 8.

Originally Posted by Purplefade

Spit balling here but what about the anti knock sensor? Maybe its not pulling timing at lower rpm?

Knock sensor is a good guess, thanks - I will try to run a diagnostic

[danny_acs]

So this has now been fixed, and I'm reporting for the benefit of everyone else that might have this issue in the future.

CPC Performance Engineering in Amersham near London took the car and inspected it. It turned out that the eccentric valve shaft had a lot of wear. They adjusted the motor on the left bank, so the knocking is gone for now. They advised that if comes back, the shaft will need to be replaced, which is an expensive job... Many thanks to them, professional job!

[Purplefade]

Outstanding, many thanks for following up with the thread and I’m very glad you’ve got it sorted


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