A6 Allroad, 2.5 tdi high pitched whine

[jonnboy32]

Hi, Hoping someone has a suggestion as to where to look to either reduce or eliminate the annoying whine from the engine. Appreciate sounds are hard to describe in words but will give it my best. It happens either when revving in neutral or accelerating in gear, although over 40mph you can't hear it. It's similar to a turbo noise but isn't a normal turbo whistling noise.

It's best described as similar to a dodgy car radio install where you had interference from the electrics coming out of the speakers (if that makes any sense!!). i.e gets louder when you accelerate and is fairly high-pitched. Car is the 2.5tdi V6, manual gearbox Allroad.

Other than this - nothing else wrong with the engine that would give me cause to be suspicious, recently serviced etc.

Cheers.. John

[Peter D]

Assuming the noise stops as soon as you take you foot off, I would initially a boost air leak. However you do not get much boost then the car is not under load but have a listen around using a lenther of screen wash pipe. Also listen to the intercooler they have been known to develope small holes that can whistle. Be carefull you do not catch the end of the pipe in any rotating parts. Regards Peter

[jonnboy32]

Thanks Peter,Noise tails off when you take you foot off the gas and falls in-line with the revs. Any hinters where to listen/look out for small holes? To get to hear the noise the have to rev the engine fairly hard in neutral so it's quite hard to pin-point the whine..John

[Peter D]

As I suggested you do not get too much boost when stationary and from what you describe I do suspect a boost leak. Check the turbo output pipe. the connections to the intercooler and ccoler itself and the pipe and connections to the throttle body. Regards Peter

[jonnboy32]

Thanks Peter,

Had a good look but nothing obvious. I did notice though that there is a slight, what looks like oil, leak from the front offside Turbo Inlet manifold (think that's what it is - at the front of the engine). It is a little smokey on hard acceleration as well.

Have more time later so will have a better look. Do I need to remove anything to get to any of the pipes to check?

Cheers

John

[Peter D]

That is quite common. A fine oil mist is carried in the boost air and accumulates at low points and in the bottom the intercooler. However the oil you can see indicates a leak so it may require nipping up. You should undo your oil filler cap and get an assistant to rev the engine to see if the cap is being pressurised. If it is it implies the crankcase breather is clogged up. Regards Peter

[jonnboy32]

Hi Peter,

Thanks for that - have now done a little research and see a plan coming together:

1/ Do a thorough check on all the pipework for the turbo
2/ Check crank case breather isn't clogged
3/ Remove inlet pipes and give a thorough clean, replace and ensure tight
4/ Check turbo and if necessary remove and strip / clean (last resort!!).

Anything else to do before getting to stage 4? or to worry about at stage 3?

Boost air leak - is this when the actuator is stuck (stage 3 in my plan!)

Will also give it a full service and a dose of Forte Injector cleaner as well.

Cheers

John

[bagpipingandy]

I had a similar whine related to engine speed, after exausting a turbo leak/whine, i found it, it turned out to be an idler pully for the aux belt.

[jonnboy32]

Thanks Andy,

Anything I can do to check that without major surgery? Cambelt isn't due for another 30K so hoping it wouldn't be the front off to check / replace.

Just been over the car and had a good check of all the piping to the Turbo and nothing untoward, although a few of the hose clips needed another turn or so but they certainly weren't loose.

Cheers,

John

PS - been away for a few weeks - compressor all stitched back together and heading off for a long drive (that's after I washed off all the bits of rust that drops out from the compressor mountings!!)..

[Peter D]

Andy is referring to "an idler pulley for the aux belt" not the timing belt. With your comment "tails off when you take your foot off the gas and falls in-line with the revs" may well point to the idler. Regards Peter