A6 2.0tdi - another niggle
Discussion
Another little niggle has appeared on my 2006 A6 2.0 tdi - a strange sort of noise that only seems to occur some times, usually when setting off in the first 2 or 3 gears and worse if I back off the throttle quickly before changing gear.
It's hard to describe the noise; it's a sort of 'woofle' - a bit like when the diverter valve on a petrol turbo has a dodgy diaphragm and the air gets chopped by the blades (so I understand it). Yet I don't think TDs have diverter valves.
It is not a major issue, merely an annoyance as again "something's not right".
Any ideas as to what it could be? And the size of the bill to fix it this time?
It's hard to describe the noise; it's a sort of 'woofle' - a bit like when the diverter valve on a petrol turbo has a dodgy diaphragm and the air gets chopped by the blades (so I understand it). Yet I don't think TDs have diverter valves.
It is not a major issue, merely an annoyance as again "something's not right".
Any ideas as to what it could be? And the size of the bill to fix it this time?
They all make that noise, its the sound of the turbo boost suddenly having nowhere to go, compressor stall I think is the technical term, Yes sounds just like a dump/diverter valve, and correct the TDI dont have one, its just what it sounds like.
Now, it should always have made this noise, but if its suddenly getting louder than before could be a number of things, you could have a boost leak (slit pipe or intercooler), or and exhaust or EGR leak, or it could be as simple as the air filter not fitted quite correctly.
Has any work been done recently? air filter change etc.
Is there more black smoke on full throttle acceleration than normal, other sign of boost leak.
You should be able to replicate it without even driving, full throtle upto 4000 then jump off, just sitting there stationary from idle. If you think its a boost leak, have someone rev the engine and have a listen under the bonnet and by the intercoolers.
Now, it should always have made this noise, but if its suddenly getting louder than before could be a number of things, you could have a boost leak (slit pipe or intercooler), or and exhaust or EGR leak, or it could be as simple as the air filter not fitted quite correctly.
Has any work been done recently? air filter change etc.
Is there more black smoke on full throttle acceleration than normal, other sign of boost leak.
You should be able to replicate it without even driving, full throtle upto 4000 then jump off, just sitting there stationary from idle. If you think its a boost leak, have someone rev the engine and have a listen under the bonnet and by the intercoolers.
Thanks again. I've never really noticed it before but it can be quite pronounced at times now. Come to think of it, the air filter housing has been removed recently in order to fit a headlamp bulb though IIRC it may have been doing it before that work was done.
I'll check the things you mention and see if it resolves it, but thanks again for your input.
Chris
I'll check the things you mention and see if it resolves it, but thanks again for your input.
Chris
Had a bit of a look today - I took the filter housing lid off and made sure the filter was seated, then put it back so it was properly sealed. I noticed the last couple of days that at light throttle pressure with a cold engine (air temp 20degC) there was a bit of stuttering.
I've also recalled that the strange fluttering sound, or woofling as I called it, seems to occur when turning but is intermittent.
There is no more black smoke, the mpg and performance seem the same, and it is not losing oil or coolant. One other thing I remembered from a while back was that the engine, though not itself sounding noisier, seems to be more 'vocal' - a deep sound to it when accelerating hard, akin to a blown or holed silencer but nowhere near as bad and with no raspiness.
I'm sure all these symptoms are related and I will need to find time to get under the car to look. Is there anything specific to check, other than that listed above? How would one check the EGR valve (I cleaned one out on a 1.9tdi once - full of oily soot after 170K miles but worked perfectly well - I was just curious to see what it was like) ?
Cheers.
I've also recalled that the strange fluttering sound, or woofling as I called it, seems to occur when turning but is intermittent.
There is no more black smoke, the mpg and performance seem the same, and it is not losing oil or coolant. One other thing I remembered from a while back was that the engine, though not itself sounding noisier, seems to be more 'vocal' - a deep sound to it when accelerating hard, akin to a blown or holed silencer but nowhere near as bad and with no raspiness.
I'm sure all these symptoms are related and I will need to find time to get under the car to look. Is there anything specific to check, other than that listed above? How would one check the EGR valve (I cleaned one out on a 1.9tdi once - full of oily soot after 170K miles but worked perfectly well - I was just curious to see what it was like) ?
Cheers.
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