Multivan Turbo noise

[Silver Caravelle]

Hi all,

I now have about 4000K's clocked up on the Multivan TDI. I took it for a country run on the weekend. I noticed at one stage that the engine started running rough for a period when in neutral at about 1300 RPM whilst pulled up for little while. I also heard the turbo making slight 'rumbling' noise (almost like starter motor disengaging noise) whilst listening to the engine revving at this point. Having said that, the turbo spins freely, and as it starts to spool up under load from say 1200 RPM there is a whooshing noise -which I suspect is normal as air is sucked into the turbo?

After a while the engine was smooth again.

I did also notice this behaviour one other time on the very first day I picked the Multivan up from the dealer and completed a 500K trip and as I pulled up in the driveway the engine ran rough and the 'turbo rumbling noise'. My initial thought was the turbo is stuffed on brand new vehicle. I have heard that this might be to do with the particulate filter doing its stuff?

What are your thoughts? Could the turbo 'rumbling noise' simply be a air bleed off noise when the turbo winds down and when the particulate filter is burning off. It doesn't sound like a turbo bearing noise and is not an noise easy to decipher. I hear the 'rumbling noise' for a couple of seconds when switching off the engine when the turbo slows down. How quiet should the turbo be on these engines?

Regards,

Scott

[Rebuild]

i tend not to notice the turbo up to 2000rpm,then after that you can definately hear it particularly on overrun.

If it bothers you,take it back to the dealer(surely it's under warranty),try to replicate the noise and see what they say.

[Silver Caravelle]

Steve,

Thanks for the reply. I was seeking to gauge initial thoughts before deciding to waste a day back at the dealers for further investigation.

Regards,

Scott

[BobD]

Scott,

My 2007 Multivan is up to about 50,000km now and has had the rough running at idle you are talking about as long as I can remember. It comes and goes and seems to be worse when the fuel level is low. It is very annoying when it happens as it is quite severe but 90% of the time it is perfect. You really notice it when approaching traffic lights and while idling but it has no other affect on the engine. The dealer has also experienced it but had no answer and there are no fault codes. He thought there must be a fuel blockage but I said it can't be as there is normal power at all other revs. They looked into when the tank was nearly empty and it was at its worst but could not think of a reasonable explanation. I also thought it could be related to the particulate filter in its heating / burn off cycle as it mainly happens around town but the dealer reckons it isn't.

It is doing it less at the moment after they replaced the O2 sensor and the exhaust gas temperature sensor (I think) to get the exhaust quality fault light to go off. However it still does it, just less frequently than before. It was the latter sensor that fixed the fault light, not the O2 sensor.

I don't know what the turbo rumble you mention is. I can never hear anything from my turbo. There is plenty of fan noise in the engine bay (usually the A/C / heater fan) when you idle and shut down the engine and you can hear it (the fan) slow down as you turn off the engine. You may be confusing this with a turbo noise.

I mentioned it once before but if you hear a strange buzzing or annoying rattling noise seemingly coming from the engine, which can sound like the turbo doing something funny, check the plastic screws holding the under bonnet trim onto the front cross member that the bonnet closes onto. You can see the large flat screws there when you open the bonnet and if they are not tight they allow funny noises that are quite loud and annoying. It took me a few weeks to figure this out after mine was making strange noises while driving, immediately after a service. Tighten them up and no more noise. On mine, it was the one on the drivers side that was loose. I was getting really annoyed with it because it was so quiet prior to this little problem and it suddenly seemed like the engine noise had increased. Very simple fix though.

[gregozedobe]

Can't say I've ever noticed any strange noises on mine (done 37,000Km so far). I don't really hear the turbo, only a low pitched "warbling" noise from the injectors (I think) up hills at 1,800 to 2,200 rpm.

Rough running and high revs can be the DPF burning off the soot (IIRC VW call it "re-generation"), but I wouldn't expect that to be happening at the end of a 500Km trip (only near the beginning if you've been doing lots of stop-start driving previously).

Maybe check that none of the intake/intercooler hoses has started to come loose and is leaking air (it is fairly common) ?

[Silver Caravelle]

Hi All,

Thanks for your feedback. Much appreciated.

I checked out things out a little further last night and took it for a spin. All seems to be fine and no leaking turbo hoses.

The Turbo 'rumbling' noise, I have isolated to the turbo slowing down when backing off under load (bleeding off air noise??). It is definitely not a turbo bearing noise. The noise can be replicated if you rev the engine in neutral and then turn it off (causing some sort of 'air vacuum rumbling bleed off ' noise). Also if one is driving in 6th gear at low revs (say 1300 RPM) under load - at the point of spooling up the turbo and take the foot of the accelerator quickly, the same noise can be heard. I am sure this is normal.

The rough running on two occasions I will put down to the DPF - for now but will monitor. Yes strangely, the first time was on the day of delivery after 500 km round trip. Last week it occurred the next day after a 250K trip after driving for about 15 mins. Apart from the brief rough running on those two occasions, if one revs it in neutral at about 2000 RPM in all situations, there is slight uneven running at about 2000 RPM and it is fine above or below these revs. Idle is very even.

Regards,

Scott

[Silver Caravelle]

Scott,

My 2007 Multivan is up to about 50,000km now and has had the rough running at idle you are talking about as long as I can remember. It comes and goes and seems to be worse when the fuel level is low. It is very annoying when it happens as it is quite severe but 90% of the time it is perfect. You really notice it when approaching traffic lights and while idling but it has no other affect on the engine. The dealer has also experienced it but had no answer and there are no fault codes. He thought there must be a fuel blockage but I said it can't be as there is normal power at all other revs. They looked into when the tank was nearly empty and it was at its worst but could not think of a reasonable explanation. I also thought it could be related to the particulate filter in its heating / burn off cycle as it mainly happens around town but the dealer reckons it isn't.

It is doing it less at the moment after they replaced the O2 sensor and the exhaust gas temperature sensor (I think) to get the exhaust quality fault light to go off. However it still does it, just less frequently than before. It was the latter sensor that fixed the fault light, not the O2 sensor.

I don't know what the turbo rumble you mention is. I can never hear anything from my turbo. There is plenty of fan noise in the engine bay (usually the A/C / heater fan) when you idle and shut down the engine and you can hear it (the fan) slow down as you turn off the engine. You may be confusing this with a turbo noise.

I mentioned it once before but if you hear a strange buzzing or annoying rattling noise seemingly coming from the engine, which can sound like the turbo doing something funny, check the plastic screws holding the under bonnet trim onto the front cross member that the bonnet closes onto. You can see the large flat screws there when you open the bonnet and if they are not tight they allow funny noises that are quite loud and annoying. It took me a few weeks to figure this out after mine was making strange noises while driving, immediately after a service. Tighten them up and no more noise. On mine, it was the one on the drivers side that was loose. I was getting really annoyed with it because it was so quiet prior to this little problem and it suddenly seemed like the engine noise had increased. Very simple fix though.

Bob, Thanks for details. I think these PD engines have a pump for each injector. With your rough running makes one wonder whether it a faulty diesel pump on one of the injectiors, but has not thrown a code? Just a thought.

Regards, Scott

[BobD]

Scott,

There is nothing wrong with my engine any more than there is anything wrong with yours. Just as you experienced, mine runs rough occasionally at idle. I was just telling you that I had mine investigated a bit and they could not explain why it would idle roughly at certain times, usually after a run on a freeway and with less than a quarter of a tank of fuel, but not always.

I was lucky that the mechanics experienced it while they were doing other warranty work, so at least the possible fault has been recorded if it gets worse later. Since it is pretty random it was good that it happened to them, even if they don't have an explanation. There is no evidence of a problem under load and it usually runs perfectly.

[Silver Caravelle]

Scott,

There is nothing wrong with my engine any more than there is anything wrong with yours. Just as you experienced, mine runs rough occasionally at idle. I was just telling you that I had mine investigated a bit and they could not explain why it would idle roughly at certain times, usually after a run on a freeway and with less than a quarter of a tank of fuel, but not always.

I was lucky that the mechanics experienced it while they were doing other warranty work, so at least the possible fault has been recorded if it gets worse later. Since it is pretty random it was good that it happened to them, even if they don't have an explanation. There is no evidence of a problem under load and it usually runs perfectly.

Bob, Sorry if I misinterpreted from your comments that yours was idling rough more than occasionally. Hence the suggestion regarding the injector pump.

Mine has very smooth idle at all times. The rough running I experienced only on two occasions that I have noticed was at slightly higher revs ( noticed in neutral -not under load) more in line with when the turbo started to spool up.

I now believe this is DPF regeneration related. However the turbo was also noisier at this point which would indicate a relationship between DFP regeneration process and Turbo behaving differently. The turbo noise I can now explain as likely to be the waste gate valve doing its thing as the turbo slows down quickly on over run after the turbo being under load - which is normal I understand. The same turbo noise is also experienced when it was running rough during the presumed DFP regeneration process. Therefore the waste gate mechanism may play a part in the DFP regeneration process.

Many thanks, Scott

[gregozedobe]

AFAIK modern VW TDIs (ie diesel turbos) don't have wastegates, but they do have variable angle vanes in the turbo which direct exhaust gases to help generate maximum boost at low revs and also prevent too much boost at higher revs.

No standard diesels that I know have a blow-off valves (BOV). Diesels don't need one as there is no intake air restriction and therefore no high pressure spike to deal with when the accelerator pedal is suddenly released. I have heard of people wanting to install them as they like the "phhsssst" noise they make, but they don't make mechanical sense.

My understanding is the DPF regeneration process injects extra fuel late in the combustion cycle so this surplus, unburnt fuel can make it to the DPF where it burns, increasing the temperature inside the DPF enough to burn off the accumulated soot particles. It has various sensors telling it how much restriction there is inside the DPF, when it gets too restrictive it initiates the re-gen.