galaxy TDI resonance sounds like raspy exhaust or something else driving me nuts

[Galaxy130]

getting really fed up with this! Galaxy TDI 130 55 plate, manual - a horrible resonance when revving up and lifting off. Similar to a slight blowing exhaust but I cant see it blowing anywhere and the car's just passed its MOT.

I thought it might be the airbox and air intake but all manner of pushing, pulling and prodding the airbox doesnt make any difference to the engine note. Its kinda like the old morris minor exhaust sound which "rasps" when you lift off (but not as bad as a MM!) Just listened to a youtube vid with a Honda S2000 described as having a raspy exhaust and that sound just about sums up mine only its the diesel version!!

I guess the first thing I need to know is ANY type of exhaust/ manifold blow an MOT fail?

or any ideas welcome as to whats causing this?! Had the car 6 mths and I think its getting worse.

[Chrispb]

It's probably turbo flutter back pressure, it's quite common

[Galaxy130]

I had a listen to an example of turbo flutter on YouTube and its a very distinctive fluttering sound - but mine doesnt do this, its a heavy resonance sound....

[Chrispb]

What about the plastic sound deadening cover on top of engine is it a tight fit on the mounting posts?
I managed to get a hose clip around one of mine that was a bit lose.

[Galaxy130]

yep, tried that! still got the sound with the cover off. Engine sounds kind of strangled to me. Its done 135K btw (well serviced by previous owner)

[Chrispb]

Just a thought has it had the EGR blanked off? if not may be worth a look inside anyway in case valve stuck open, also check manifold flap valve.

[Galaxy130]

Chris, thanks for all your advice. Is there any way I can check EGR is closing without taking it off? Also, what constitutes the manifold flap valve ie where is it?!

[Chrispb]

Start by removing the scuttle/bulkhead tray for better access
You can visually look through the valve with the aid of a mirror after removing the air charge pipe.
There are two vacuum pipes on the EGR valve,the one on top of  the large dome operates the  exhaust valve this is held shut by spring pressure and is opened at varying throttle positions by vacuum on the large diaphragm.
The manifold flap control diaphragm is slightly hidden behind the body of the EGR this is a smaller vacuum pipe, under normal engine running the flap should be fully open, the valve should shut momentarily when engines switched off.

More info on cleaning below

https://www.fordmpv.com/smf2/ford-galaxy-reference-library/galaxy-mk2-intake-manifold-cleaning/

[Galaxy130]

ok thats great, will take a look in due course and let you know how I get on

[insanitybeard]

IF it's none of the above, have you checked the crankshaft pulley to see if the rubber bonding that holds the inner and outer sections (as arrowed in the below picture) has started to crack? Not sure if it would cause the raspy noise or resonance you mention and without hearing it first hand it's always hard to be sure but could be worth a look, as well as maybe the alternator belt tensioner, the freewheel clutch in the alternator pulley, air con compressor pulley etc....

Does the noise disappear once the revs have lifted off idle? Is there any detectable vibration to accompany the noise? Is the noise audible regardless of whether the vehicle is moving or stationary?

[attachimg=1]

[Chrisl]

Just had something similar with my S-Max. Different garages had different suggestions ranging from gearbox input shaft, DMF and turbo through to crankshaft pulley failure. Turned out to be the aux belt tensioner and alternator clutch pulley - the crankshaft pulley on the S-Max 2.0 TDCi is solid so was ok. The engine is now totally transformed, much quieter and smoother.

Can't say your fault is the same, but it's worth investigating.

[Galaxy130]

Hi Insanity, I havn't checked the EGR as I am flat out with work and will so as soon as I can. RE. this "noise" if I was to put money on it I'd say it was exhaust related. Theres a bad resonance/ drone that reverbarates through the cabin rather than physical noise, its there when you rev up at stationary in neutral - seems to come in at 1500rpm and peak around 2000 I would say. Lots of info re. resonance on the Passat on the net, concensus seems to be exhaust related - flexipipe issues, broken up cat etc. It completely spoils what is essentially a nice car!

belt tensioner was replaced about 20k ago. I'm sure its resonance caused by induction or exhaust rather than mechanical.

For those that can recall - think back to the Morris 1000 when you lift off the throttle and hear that raspy exhaust note exclusive to the Moggy thou!! ....not nearly as bad as that but same type of noise.....

[Galaxy130]

Chris, sorry we posted at the same time - I will check these things also the crank pulley etc

[Galaxy130]

ok just pulled the thing to bits and think I've found the problem. Theres a hard plastic pipe running from the turbo to the flexible pipe that fits to the airbox. On the hard plastic pipe theres a metal angle bracket that bolts to the hard pipe and then to the back of the engine  block and this bracket has fractured in two so the whole pipe assembly is not anchored thereby presume is vibrating and resonating thus giving me my noise (I hope)  Looked into the EGR valve with a mirror and the valve is seated when engine off. theres black crud in there but not excessive, the stem presumably is moving as the crud is missing on a portion of the stem. How can I tell if the EGR valve is opening when required?

[insanitybeard]

If the valve stem is clean on the section closest to the diaphragm then that would suggest the valve is doing something as you say, you'd know if the carbon/sludge buildup was excessive- it's be something like this! If you want to observe the valve moving and you've got a mityvac (hand vacuum pump or similar) just connect it up to the diaphragm, apply a vacuum and see if it moves- obviously you'll need to take the boost pipe that connects into the EGR valve off to see this.