Hi all,

 

I'm getting a slight gurgling kind of noise under load in 3rd, 4th and 5th - being most audible in 4th and 5th. It starts around 1500rpm and stops around 2000rpm - if I keep the revs above or below this it doesn't seem to do it, similarly having the revs in this range but not accelerating doesn't cause the noise. It's not a full on hiss such as an air hose being off - having had the intercooler shed it's pipe recently it doesn't sound the same. There's no loss of power either, though my mpg does seem to be down by about 3 to 4mpg (which may not be related as I have had new tires, the aircon regassed, a new intercooler and new alternator recently so any of these could be causing the decrease?).

 

I took the car into DS Motors in Milton Keynes and the mechanic drove it, he confirmed the noise and suggested it was boost related, but said that as it's so minor and doesn't affect performance it would take a long time for them to find it and it probably wouldn't be worth it financially - if I wasn't so easily bugged by things like this I would agree!

 

Does anyone have any ideas as to the cause of the noise and/or my reduced mpg?

 

EDIT: should have mentioned, it's an '04 130bhp 1.9tdi with 109,000 on the clock

Edited 19 May, 201412 yr by Flurry

Gurgling or is it more like groaning, like somethings being stressed?

I would say the DMF on its way out by the sound of it.

They can get REALLY noisy before they completely fail.  

Original clutch/dmf? On that mileage it's probably nearing time for

a new kit. 1500 to 2000ish is where your torque peaks on standard mapping.

Food for thought...

Oh and MPG could be down due to clutch slippage in higher gears.  

Gurgling or is it more like groaning, like somethings being stressed?

I would say the DMF on its way out by the sound of it.

They can get REALLY noisy before they completely fail.  

Original clutch/dmf? On that mileage it's probably nearing time for

a new kit. 1500 to 2000ish is where your torque peaks on standard mapping.

Food for thought...

Oh and MPG could be down due to clutch slippage in higher gears.  

 

Not much like groaning, more like liquid being sucked/bubbling through something - it's not air in the coolant though according to the mechanic.

 

I believe it's on it's original clutch and DMF as there's no sign of a change marked in the service logbook, though I've only owned the car from 75k miles. Wouldn't you expect some loss of power if it was clutch slippage? Is there any way to test the clutch or DMF?

I believe this problem is caused by resonance or rattling in the air intake duct between the slam panel and the air filter box. The Audi version of this vehicle has a much stronger and ribbed duct - and it doesn't rattle.

 

I have made a huge improvement to the noise by wedging a shaped piece of closed-cell foam polyurethane pipe insulation between the duct and the air filter box. I have also sealed the joint (to limit vibration) where the duct push-fits into the air cleaner box, using a non-hardening compound so it comes apart.

 

I did this soon after getting the vehicle and forgot about it - until I drove another one.

 

The design c o c k ups in this vehicle just never cease to amaze me - I thought I'd paid the designers when I bought it...

 

rotodiesel.

Edited 19 May, 201412 yr by rotodiesel

Please excuse my ignorance, is the slam panel the ducting that comes from the front left of the grille and runs back to push down on top of what I presume is airbox? If so, I've had problems with this rattling before, and currently have a thin band of tape around the edge of it to damp the rattling - maybe this isn't sufficient, should it be totally airtight? Am I in the right place, or are you talking about the filter at the top right of the bonnet under the scuttle?

 

Couldn't agree more on the number of blatant flaws it has, though the upside is I'm learning a lot from it as I go! Time will tell if I regret my choice, though it does eat up miles well.

Yes, it's the engine intake duct from behind the grille to the main air filter box.

 

If you sort out the (sometimes unbelievable) c o c k ups and look after it, a 1.9PD Superb will run to starship mileages.

 

I've posted quite a few of the problems I've found on this Forum over the years...

 

Pinch bolts, anyone?

 

rotodiesel.

I'll have a look at the ducting in the morning then, fingers crossed it's this rather than the DMF or clutch! Is either end of the ducting more likely to be causing this or should I try and seal both?

I've worked my way through some of the flaws, such as the cabin air filter seal and plenum chamber bung. It's done 33.5k miles in the last year and a half, with relatively few issues.

Thanks for the help guys

EDIT: if the ducting is the cause of the noise, could it also be causing the lower mpg?

Edited 19 May, 201412 yr by Flurry

I noticed the small cover on the driver's side of the engine bay also rattles on the top of the pipes it covers.  When I bought the car it looks like someone had put a small piece of foam to stop this, but it has now gone missing.  Another job for the weekend...

Would it be safe to temporarily remove the cover that sits over the top of the pipe/ducting to eliminate it or identify it as the culprit? As far as I can tell it's only cosmetic, but I don't want to try running without it if there's a good reason it's there!

It would be safe to remove the duct, but the increased intake noise would make it difficult to know if you had fixed the resonance.

 

The cover over the air box rattles if it's pushed too far down - it then fouls the duct. I cut a section of rubber grommet and lined the "clip" to stop this from happening. The largest diameter of the clip needs to engage with the rubber - which is not the case if you push it right down.

 

Wolfsburg numpties.

 

rotodiesel.

I meant the cover over the duct rather than the duct itself, though it's worth knowing that it's safe to run without the ducting too.

 

I'm confused why it only makes the noise when accelerating - if you rev it in neutral it doesn't cause the noise, even at the correct rev range.

An engine under load produces a completely different noise and vibration profile. The mountings are stressed due to torque reaction and the position of the power unit changes due to this.

 

rotodiesel.

An engine under load produces a completely different noise and vibration profile. The mountings are stressed due to torque reaction and the position of the power unit changes due to this.

 

rotodiesel.

 

That makes sense, thanks for explaining that!

 

If it does turn out to be the air ducting could it also be causing the reduced mpg?

No.

 

rotodiesel.

That's what I feared as it still leaves me down on mpg with no obvious cause! Thanks for the help rotodiesel

It might be worth a visit to Unit 18 in Old Wolverton for their expertise.

Thanks for the recommendation DGW, shall try and pop in there sometime this week.

 

I've removed both the ducting cover and then the ducting itself - neither made a difference to the noise

Pinch bolts.. lol i laughed when i saw that... I've had so many problems with those. 

I noticed the small cover on the driver's side of the engine bay also rattles on the top of the pipes it covers.  When I bought the car it looks like someone had put a small piece of foam to stop this, but it has now gone missing.  Another job for the weekend...

 

Mine's been doing that too.  I happened on a huge rubber 'o' ring in my garage, which holds it down nicely now.  Didn't make a jot of difference to any of the odd noises I'm trying to track down  :wonder:

 

Gaz