Dry Grinding/abrasive noise on throttle release from A4 TDi Sport 130

[imported_sguilliard]

Hi,

Today I have noticed that I get a strange dry grinding noise from my car when I release the throttle.

It happens worst when the engine is below 2000rpm; when gently applying the throttle so that the engine starts to labour, the noise appears for a split second as soon as you release the throttle. It is most noticeable in 3rd and 4th gear.

The sound appears to come from the driver's side (right) of the car. I did originally think that it might be the clutch as I noticed the sound when changing gear. However, leaving the car in 3rd driving at approximately 30-40mph the sound occurs every time I release the throttle.

It almost sounds as if the gears haven't got enough oil or something; it's a very dry sound.

My car is only 16mths old and has 37700 miles on the clock so it will still be under warranty, but I'm hoping that someone might be able to suggest what the problem could be before I take it into my local Audi stealer.

 

[audi5e]

could be a mechanical componant that briefly touches something else as the weight of the car shifts when you back off the throttle?

 

[imported_sguilliard]

A friend of mine has suggested that it might be the valve on the turbo; he hasn't actually sat in the car to listen to the noise yet, but from my descriptions that is what he suggested

He used to be a machanic for Benneton F1 & Prodrive so know a fair bit about these sort of things.

Has anyone ever come across this before?

 

[imported_Lesr]

If you get the sound whilst in gear, but on the over- run (ie no throttle) but always at the same speed, it could be transmission whine.

I have had this in previous cars, and it is present to a degree in my 51 plate A3 (TDi 130 6 speed). It was checked at last service, and all oil levels etc were fine, the sound it not overly loud, and the drivability of the car is unaffected, so I just live with it!

If this is the case, then unless you can persuade Audi that it is outside their 'tolerances' (they may invite you to try a similar car for comparison) you will have to live with it too!

 

[imported_sguilliard]

I don't think it's transmission whine; it would surely make the sound for longer than the split second immediately after quickly lifting off the throttle, that it is doing so at the moment.

The sound only occurs most noticeably at close to 2000rpm and is loudest (although it's not loud at all and you need to listen for it) when you open the throttle up a fair bit before immediately lifting off the throttle very quickly. It doesn't happen if I ease off the throttle more gently.

Over 2000rpm there is no noise when lifting off the throttle, whether gently or suddenly.

The sounds has a dry abrasive quality to it, which is why I am concerned about it. However, if it is pressure being released from the turbo then the sound could be likened to a slighlty rougher sounding version of Darth Vader breathing; I will let my mate have a listen this evening and then my local Audi stealer and report back here...

 

[imported_sguilliard]

Ok, well after having my car for over a week, my local Audi stealer tells me that I need a new turbo.

They have ordered the part and will fit it tomorrow. I'm surprised that the turbo needs replacing on a car that is less than 18mths old with 38k miles on the clock!

Is this a known problem or have I just been unlucky?

 

[imported_Lesr]

It's recommended to 'simmer' the turbo after it has been working hard by letting the engine idle for a minute or two. This circulates oil through the turbo bearings and allows them to cool down. switching off straight away deprives the turbo of its much needed lubricant supply, and can cause any oil left in the bearings to 'carbonise' due to the extreme heat generated by this device.

You can imageine how damaging this can be in only a short period of time, and this may be what has happened in your case.

All just my humble opinion of course!

 

[imported_sguilliard]

What do you define as 'working the engine hard'?

Nearly all my journeys involve cruising along the motorway with the destination always being in some town somewhere where trundling along at a snail's pace with the engine barely getting up to 1500rpm is normal.

I will certainly bear your advice in mind in future; I just can't help thinking that if everyone had to sit with the engine idling for 2mins after a journey then there would surely be a lot more turbo failures?

Hence my question in my previous post as to whether this is something that's common and also the definition of 'working the engine hard'? Is cruising along the motorway at 90mph and under 3k rpm the same?

 

[imported_Lesr]

It depends on your style of driving, and you need to exercise your judgement.

If I have been crusing at 3k rpm on the motorway for a while, and maybe pull off into a service area, I will let the engine tick over for a minute or so to let the turbo 'simmer' before switching off. If as you say, your motorway journey ends up with crawling along at a snails pace in town before stopping, then I wouldn't bother as it will have already cooled down.

You need to use your common sense with this. You should be able to feel the turbo start to come into its own at around 2K rpm, and if it's been above that for any appreciable time (over 70mph in 6th in the case of my A3) I 'simmer' before switching off. Likewise if I have been 'booting' it through the gears for any reason. I have been following this advice with various turbo equipped diesel cars for more than 10 years (though not all VAG) and have had no failures yet - but I am fanatical about oil and filter changes...

You also need to be aware that there is another school of thought that says where the turbo is water cooled (not sure if this is the case with the Audi?) you may not need to 'simmer' with a modern diesel engine using high spec synthetic oils.

I personally still would though just to be on the safe side (perhaps I'm old fashioned...) and in an effort to avoid any large premature servicing bills.

Hope this helps.

I

 

[audi5e]

Turbo's operate anywhere from 80 000 to 200 000 rpm. The spindle is lubricated by the engine oil which only pumps through when the engine is running. Bear in mind that it takes quite a while for the turbo to slow down.

Where I come from, the turbo's operate closer to 200 000 rpm, and that just to be able to get the same boost as a coastal (low altitude) car would get from the turbo spinning at half that speed.

A couple of years ago, Isuzu (Mitsubishi) introduced a new 4X4 double cab onto the local market.
Within a couple of months hundreds of them started to have turbo failures. The reason, the turbo's were spinning at nearly double the speed that they had been designed to run because of the lower air pressure in Johannesburg. So to get to the correct pressure in the manifold the turbo had to spin a lot faster....

So the problems with turbo's failing is more to do with a sudden lack of lubrication on the bearings from the driver switching off too soon.

 

[imported_sguilliard]

Well, it seems that the noise isn't coming from my turbo anyway; I have had the turbo changed under warranty as the dealer thought that was causing the problem.

Got my car back yesterday after being told that the problematic noise had disappeared; it seemed ok on the drive home but this morning it has reappeared albeit not as severely!

I'm beginning to think it's something to do with the transmission. I notice that when the engine is labouring in too high a gear, releasing the throttle quickly generates this noise. The noise lasts only as long as it takes to quickly lift your foot off the accelerator. The noise also seems to vibrate in time to some movement that comes from the gearstick at the same time.

Anyone with any idea what this could be before I go back to my Audi dealer again?

 

[imported_sguilliard]

Well, before taking my car back to the dealer I had a friend listen to the car; he's a mechanic for a well-known F1 team.

He told me that the sound was definitely the wastegate on the turbo, but wasn't sure if the noise was a problem.

After taking my car back to the Audi dealer they have advised me that the noise is normal and given me a printout from the Audi intranet confirming this and describing my problem in detail. However, I don't ever remember hearing the noise before.

I am prepared to accept that I noticed the noise initally because it was louder before the turbo was changed and that I still notice it because I'm listening out for it; it's a very quiet noise and some passengers in my car have been unable to hear it all which was infuriating.

Does anyone else have this on their 1.9 or 2.0 TDi? Apparently, according to Audi it is normal on both engines.

 

[mini-me]

Hi there... I have the same problem. Did you ever resolve the issue?
Cheers

 

[mini-me]

UPDATE - Eventually solved the noise after the cambelt tensioner and other bits collapsed.
The car just cut out when driving along the M42. It would start, then stall if not under load... very odd.
Little did I know I was potentially going to blow the engine up!... to my eventual cost.

Quite how the belt didn't come off has baffled the mechanic after driving it home with it stalling all the time.
It was very loose, but fortunately hadn't skipped a tooth.

Anyway to cut a long story short, with all sorts of other peripheral stuff getting damaged (see the bill below), £1666 lighter, the noise has gone!

So don't ignore this noise is my advice... ask them to take a look at the cambelt, and have youself a (really) nice holiday instead...
Oh yes... And if it happens to you...don't keep driving either!