HELP - Sick V6 TDi

[S2central.net]

I need some advice from the diesel doctors out there. Its the first diesel I have owned and never heard this kind of sound before. Its the Audi V6 2.5TDi engine - circa 2001.

Luckily it has only been making the noise for a few hundred yards from home - the missus nursed it in. It sounds expensive to me - is this the noise of a fuel injector not working or the pump gone bad ?

Its a mighty thump but akin to a misfire noise - its not a mechanical thunk like a bearing. Oil levels and temps all fine. I haven't pulled codes or anything yet. Just looking for any advice or BTDT.

Doesn't sound 'blowy' like a cracked manifold either. Noise is definitely from drivers side of engine, but difficult to say more than that.

MP4 attached so you get the full effect.

Any insight much appreciated.

[S2central.net]

Attached MP4

[s2driveruk]

not the same engine Paul but my A6 made that noise shortly before the entire pulley mechanism sheared off the a/c pump!

They have a history of this issue too the a4/6's so might be worth a look as its rev/speed related given its on a belt and it sounds like that on the clip.

Prepare for a £300 bill if it is the case....

[Error404]

I was going to suggest a pulley rated issue too
I had someething very similar when my alternator housing was cracked - rattled just like that.
Check the pulleys and bracketry on the PAS & AC pumps and the Alternator & belt tensions etc

[S2central.net]

Thanks chaps. I did all the belts *properly* with new tensionsers etc a couple years ago. The noise does sound low down and I think aircon is that side. I have checked that all injectors are getting fuel so it ain't the pump - which is probably a good thing.

Next job is overalls on and undertray off for a look at the belts. So much for a day 'off' !

[s2driveruk]

http://www.s2forum.com/forum/showthread.php?t=26500&highlight=a6+aircon

[UR-S4]

The ribbed belt tensioner is a common failure.it fractures at its pivot point.They eat cams,usually visable through the oil filler hole,or if there is a vibration through the whole of the car consider the dual mass flywheel.I looked at an a4 for another garage who swore blind it had a misfire turned out to be the flywheel.Good luck...Just to add the bottom crank pully / damper also common come to think about it start there (end of waffle) !!

[istoo]

pray its not the fuel injection pump... they make S2 parts seem cheap.
have you read for fault codes?

There was (apparently) a bad batch of pulleys a few years ago, mine exploded a month after i had all the belts and tensioners done at the stealers, that was in 2008.

[S2central.net]

Good info lads. I'm trying to remember if the ribbed belt is just for aircon pump or if it is shared with alternator on the V6. The thought of a new aircon pump doesn't fill me with pleasure I must say but if I can at least stop the death rattle while chasing a 2nd hand one it keeps the family bus on the road.

Lunch then spanners.

[mcandmar]

The Audi gods are out to get you Paul, these V6's dont seem to like you. Only issue i've delt with on an A6 was a failed alternator pulley, there a two piece rubber damper like the crank pulley but prone to breaking apart.

[s2_wot]

Paul FWIW,
On our A6 TDI it was making a ferocious noise on the drivers side at the front. There's an electric rad fan that switches on when the climate control is on. The fan had broken away from the motor's shaft and when the motor was running it was interfering with the fan. We never figured out what actually broke the fan but with the engine switched off you'll know very easily if that's your problem.
Best of luck.

[S2central.net]

Well it gets weirder. Just been underneath and the pulleys and brackets are all fine. Little bit of slack in the ribbed belt but nothing untoward. There is no mechanical contact with viscous fan either. Its a real thumping on every engine cycle. I need to post up another vid.

The weirdest bit is that the noise is definitely loudest at the air intake - on drivers side - so I remove the duct for where air is drawn into airbox and the noise is huge there. When I placed my hand over it, not only did it quieten but more worryingly i could feel whumps of air pressure against my hand.

That airbox should always be in vacuum. I am trying to think of what sequence of events is causing pressurised air to be created on the inlet side of compressor. My head hurts with this.

I also probed around both banks with a mechanics stethoscope and found nothing noticeably different in all cylinders. The aircon compressor rumbles loudest but it's not source of the audible whump and backpressure.

Very confused here. Don't really want to start stripping until I have a solid theory.

[S2central.net]

Can only assume it's an inlet valve stuck open cos how else could pressurised air make its way back thru intercooler the turbo and airbox.

Now I need to find a diesel compression tester so I don't have to lift both ****ing heads off.

[mcandmar]

With pressure pulses back through the intake i would have said inlet valve. Having said that it would be very unlikely on a big diesel engine

[Acidburn]

Not good to see/hear paul, the allroad I mentioned to you before that I picked up still ain't sorted, its fine one minute then the next just goes flat with no power hardly so just going to sell it on instead. Shame as its fully loaded.

Your not having much luck with your cars atm, how's the others going on?