4.2 TDI engine noise
 

So, recent week my car has grown some kind of RPM-related engine noise. 2005 A8 D3 4.2 TDI (BVN)

It's not related to transmission or speed, present when in N/P just revving the engine. Cool/warm motor doesn't matter. Same goes for any load, present all the time but most apparent around 1000-1800 RPM, above that the engine itself drowns the noise.

Haven't been able to really locate the source but a qualified guess is anything going on the belt such as water pumps, AC compressor, etc.

Tried to turn off the ACC with the On/off button on the dash but not sure if there is any AC compressor clutch on this car. Turning off the ACC doesn't change the sound. Should turning off the ACC disengage the compressor?

Anyway, what is the best way to troubleshoot this? Hanging off the belt and see if goes silent?

Here's a video where the noise is present. You can hear a high-but-not-very-high pitched noise, a little bit like a sewing machine or something that follows the engine RPM.

https://youtu.be/sEZqyww4H8Y

Any ideas would be appreciated :)

Top two options would be PCV valve and low power steering fluid. Difficult to say as the video is recorded inside the car, so could potentially be other possibilities.

BTW Welcome to the forum. Pop along to the Introductions section and introduce yourself... and your car. We're a friendly bunch and appreciate seeing photos, lots of photos.

Thanks for the friendly welcome and two ideas to check out!

Guess I'll start out trying to listen to that PCV valve even though I have my doubts about that being the source. Location of that valve is pretty hard on the V8 diesel...

That sounds like bearing noise on an anciliary component. Try and record it from outside the car - both at the front of the engine and from the back of the engine near the firewall.

The D3 has an internally valved compressor I believe, so no clutch to turn off.

Will see what I can get. Moved from my house so now I don't even have a garage. Weather has been ****ty so it has to wait for the weekend. Meh...

Had some time today to listen to the engine while a friend was managing the throttle. Hard to locate any source or direction but probably from the back side of the engine, maybe little on the passenger side (hard to tell).

Engine otherwise runs like a charm, VCDS doesn't give any clues. I had an error on one of the EGR valves a month ago (before the noise appeared) but when I pulled them and cycled them with VCDS they worked just fine. No engine light since then.

I haven't followed up on steamships ideas. Just noticed that it was a pita to check the power steering fluid level. Noise doesn't change when I move the steering wheel though.

PCV valve? Hmm, hard to say anything about that. How would one know if that is bad? Would the sound come from it or would it just result in noise coming from somewhere else?

A shaky movie, held it in my hand while I listen around myself.

https://youtu.be/SsIXgsrMCVY

Sorry I can't offer any help/suggestions.
Good luck with it though and be sure to report back on any progress.

That definitely sounds like a bearings on something rotating. Could be anything from belt relay rollers or alternator/ AC compressor / power steering pump etc .

On another note my 4.2TDI also has a variety of noises the loudest /most annoying seems like a whistling kind of sound coming from the rear centre vents. It is rpm related but not directly, more like on a delay. For example no noise in idle but as you raise rpm the noise comes on slowly and if you stop at traffic lights or roundabout and rpm drop to idle the noise still keeps coming for couple of seconds and slowly dissipates, switching AC off does not affect noise at all. I notice that AC compressor shaft is a bit wet with oil and UV dye.

Check out the following two videos that might help. The first is a method of checking the various pulleys and tensioners to see if the noise is coming from them. Needless to say, once you've watched the video, if you attempt it, please be very careful.

https://www.youtube.com/watch?v=QyZWhz7uvDE

The second video I came across sounds similar to yours and may be worth checking out, although the location of the alternator may make it difficult to do what's shown in the video:

https://www.youtube.com/watch?v=hmPUUVwIJUU

Thanks for your time replying ;)

Some generic tips that seems like the next thing to do. Even though it is hard to say, it seems like the usual suspects around the belt (alternator, pumps) are not the guilty ones this time. I'll try to do some more directed listening but I prefer using a wooden stick instead of a big beefy screwdriver...

Also booked a time with my old trusty mechanics a few weeks form now. Just in case.

Tried to pull the front belt yesterday to see if the sound came from the alternator/compressor/pulleys without success. Even though I could get a spanner into the 3/8" slot on the tensioner it was a lie to move it. You would need really small hands to slack that belt to pry it off the alternator...

Had my old trusty mechanic to have a look at the car today. He was pretty confident the alternator was the source of the sound. He also noticed that the belt tensioner was in bad shape. Might even be that the tensioner is the source of the sound. Didn't ask him if he had the belt off because of the tensioner.

He had some troubles sourcing a refurbished alternator + tensioner but I guess that was due to not having the correct part numbers. Normally he doesn't treat V8's that often ;)

Can someone confirm that the alternator part number is 07 903 015Q and the tensioner 057 903 133J?

I'll see what I will do, maybe I do the job myself depending on what he offers. Looked at the repair guide and it seemed doable in a normal hobby garage without lift.

Can anyone tell if I need the special vacuum tools for refilling/bleeding the coolant system after the job?

Correct part number for the alternator is 059903015PX. The tensioner number you have is correct.

As an aside, it's a good idea to update your signature to include some specifics about your car. That makes it easier for others to identify which specific model you're referring to, although in your case you did mention this in the first post - '2005 A8 D3 4.2 TDI (BVN)'

Thanks for the confirmation!

I ordered a third-party (not refurbished/rebuilt) 059 903 015P. Let's see how that ends. With some luck it is not the alternator but some of the rollers/tensioner but in that case the alternator goes back to the supplier.

Also remember that I have some small leak on the coolant system, will need to locate and fix that at the same time. Hopefully it ends well, a long time since I spent time in the engine compartment on my car. Promise to document with some pics!

Yesterday I got it confirmed that the alternator is broken. Even though the voltage reads OK when engine is on (14+V), the battery isn't charging properly. Became obvious when all electronics started failing during drive, ending with the gear box putting itself in neutral ;)

Quite impressed the battery stood up that long. Let's hope I get the spare parts before Christmas.

Tried to locate the coolant leak today. Spent several hours trying to locate one single drop of coolant anywhere. Without success :( Let's hope it doesn't end up in the oil... (didn't look like that last oil change at least).

Any advice on common leak places? I raised the pressure in the coolant container to 1bar and couldn't locate one single drop over several hours even though the pressure slowly released. Won't be able to refill the system using vacuum after alternator change with this leak. Damn car :D

OK, you gave me your time. I give you a follow-up and some pictures ;)

So, the alternator gave up and I ordered a new alternater + a belt tensioner that I suspected to be bad. Unfortunately I missed to order the two gaskets for connecting the cooling to the alternator. Wasn't worth chancing re-using the old ones. Christmas Hollidays messed up the delivery so first chance to take on the job was this week.

I don't have that much experience working with cars but this kind of job is more of a tear-down-replace-rebuild job. I have removed the front wheel house liners + front bumper a couple of times but not more than that.

Started the job before Christmas by printing the necessary guides from ElsaWin. They are pretty OK but the main problem with all these guides is that you sometimes have no clue where a part is situated. Even with a detailed figure it is impossible to locate the area.

I used one evening to prepare for the work and to do as much as possible up until removing the lock carrier which required a few more hands than I possess.

Yesterday I started from that point. Everything took it's time but no major problems or stuck screws. Had to be creative to remove one of the screws on the motor torque support (welding a handle to a allen wrench). Also I found that some steps in the guide was easier to carry out in a different order.

With the front off, I got confirmation on the broken belt tensioner. Corrosion had cracked the spring mount. After removing the belt, the source of the noise was obvious. The alternator was really hard to rotate, bearings probably worn out.

I replaced it with a new third-party one (yeah, don't plan to own this car forever). The swap and the following re-build of everything was actually really pleasant.

The re-build wasn't made in the exact reverse order because I wanted to get the coolant system together to find any leaks early. Used a chineese kit for vacuum refilling. That was a first time, worked out really well. Then put the system under pressure for the rest of the work time to ensure no leaks.

When everything related to the engine was in place I started her up and ran through the recommended steps for bleeding the coolant system. Engine sound was back to normal and alternator was charging as it should according to VCDS.

Finally put the bumper + wheel house liners back and then cleared all fault codes caused by battery disconnection. Took her for a 15 minutes ride and again checked for fault codes. Seems fine. Really fine. Me happy ;)

A few thoughts:

- Is there any good way to locate different things in the car? I mean, it took me 10-15 minutes to locate the darn front airbag sensors event though I knew they would be somewhere in the lock carrier.

- A bit strange that the alternator failed both in bearings and in charging functionality (diodes?) at around the same time.

Five pictures from yesterday:

https://whatever.nu/byggahus/alternator1.jpg
Lock carrier removed

https://whatever.nu/byggahus/alternator2.jpg
Closer view

https://whatever.nu/byggahus/alternator3.jpg
Alternator removed, note the belt tensioner

https://whatever.nu/byggahus/alternator4.jpg
The darn thing removed.

https://whatever.nu/byggahus/alternator5.jpg
New alternator, belt tensioner and belt in place

Thanks for answering my questions. Let's see what's up next :cool: