Ok, so I just got my wee car back on the road and it's been having boost fluctuations. That problem seems to have been slowly sorting itself out (probably oil in n75, vacuum lines etc - had blown turbo)

Was out for a drive tonight and floored it......

w......t......f......is that noise?

Whenever I hit WOT there's a noise coming from the engine that I've never heard from any car before and I'm struggling to come to terms with it given the money and time I've just put into this car.

I fitted a new turbo and cleared oil from systems as much as possible, have driven it fairly calmly since it was getting boost fluctuations. Now they are as good as gone I decided to give it some welly and the noise I'm getting is not nice at all.

Really hard to describe it, like if you hiss like a cat but use your tongue to make it more raspy. Only happens at WOT, fine at all other times.

Worried I've got a duff turbo and it's the turbine trying to eat out the compressor housing or something.

I can post a short video if it helps but my phone isn't the best for recording it.

Imagine you are running with a metal stick and drag it along a metal fence, kinda like that......

Real raspy, kinda metallic noise.

Could it be a duff turbo I bought?
Anyone heard this noise before? I certainly haven't, not even before my old turbo failed.

I have driven the car maybe about two weeks since changing the turbo, oil pump and pickup, it's only just started doing this. It's a very disconcerting sound indeed.

Almost like something is loose and catching the timing belt or something but only happens at full throttle. Drives perfect at all other times.

Would appreciate any suggestions.

 

Your other post probably should have been referenced with this as well. There's some good history there. Good diagnosis requires both a decent knowledge of how the car is supposed to work, as well as a fair understanding of what the car has been through recently that may or may not have led to the condition.

Your car has certainly been abused, albeit for a short while, but driving the engine with the possibility of no oil flow is dangerous to the internal workings of the engine.

Have someone rev the engine - while the car is in park/neutral and warmed up to proper operating temp.) when you're in front listening to identify where the noise is coming from. Yes... it's going to be somewhat loud, so be prepared. Posting a vid couldn't hurt, either.

Also, you might want to try posting this in the A4 sub forum. I don't know how many of us here have experience with the 1.8.

EDIT: I say the A4 sub forum because the A6 1.8t is somewhat rare. A lot of the A4 guys have the 1.8t since it's a very common setup and essentially the same engine, but in a different chassis.

 

Hey, thanks for the reply.

I will consider posting to the A4 section if I don't figure it out myself over the weekend.

The noise only happens under load at absolute full throttle, it's purrfick the rest of the time. First thing I did was listened to it parked, I revved it hard - nothing. Listened carefully and closely at idle and only a few small clicks could be heard that sounded anything like the noise. No idea where they were coming from unfortunately.

I have also just noticed some over-cooling so I may have a small amount of air in the cooling system due to me briefly removing a pipe the other day. reaches 90 degrees but drops to around 70.
Oil is taking too long to get up to temperature too by my reckoning.

Could be it's practically toast but may just be a combo of a few small issues.
I'll keep telling myself that lol.

The noise sounds like the car has a tank full of crisp packets that it runs on at full throttle but sounds fine at 3/4 throttle. Go figure.

No lack of performance though.
(car is stock)

I think there may be a small vacuum leak somewhere as the idle is a little rough also.

I have done an awful lot of work on the engine so it may be some loose ends i missed.

I did notice it happens more readily when I shift down from 3rd to 2nd and gun it. Almost like it's something in front of the engine that only makes contact with fan or cam belt when I gun it.

I'm fairly sure the noise is external to the engine (99.9%) so either the turbo, a loose part, a reaction to coolant lock or vacuum leak, or something ancillary like an emissions system related part.....OOFT, so many potential lines of enquiry with modern engines.
I have almost always repaired my own cars so I am pretty well versed in diagnosing problems and solving them (note my first thread)......I've just never heard a noise like this one before on any car.

Crisp packet power.
Weird.

Will report back, did shoot a short video but dunno if I can upload it here or if i need to host it elsewhere and the sound is pretty guff.

I do have an EBC here so i may fit that and turn up the boost to see if the problem occurs at 3/4 throttle with more boost. If not, then the turbo is fine and it's something else I figure.
Process of elimination and all that.......

 

Quick update:
I'm convinced this is actually an exhaust related issue (or boost leak)

I found one of the bolts that mount the turbo to the manifold was bottoming out inside the threads in the turbo. Hacked a few threads off of it and replaced it. Car now makes more torque and sound isn't happening as much.

It seems people sometimes have problems with the wafer thin metal compression gaskets, leading to similar noises.

So I will be replacing both of them in the near future to see if that cures it.

I believe the problem started because the bracket that holds the downpipe to the gearbox casing broke off during removal of the downpipe and I couldn't get it seperated so i just left it hoping it would be ok (mistake, obviously lol).

Got a nut splitter coming so I'm hoping once I secure that bracket to the gearbox (transmission) housing and replace the two metal gaskets for the turbo, add EBC and replace vacuum lines (all of them.....yup, why not?), new DV.

If that lot doesn't cure it or I don't fix the problem by default as I do all that stuff then.....who knows.

Certainly seems like a boost leak from the exhaust gaskets are the cause of this problem. Lot of threads pointing to that as a culprit.

My next mission is to get a rebuild kit and rebuild the old turbo, just in case.

Will continue to update as things go on. I did shoot a video but it sucked bumpipe.
Video makes it sound like a BOV - not a true representation of what I'm hearing.

My kids said it sounded like tin foil.
And there we have it, if they say that then it must be those wafer thin metal gaskets.

 

Okay, thinking it's the manifold to turbo gasket.

Hopefully I can pull it on Sunday, weather permitting.

Going to try it without the gasket. (seems popular lol)

Finding it hard to get time and sunshine on the same day.

 

Despite the tumbleweed, i'll continue posting just in case this could help someone in the future.

At this rate though......I doubt it.

LOL

Car being a c*** diary - day 3.

Took the exhaust header to turbo gasket out - no change.

Got genuinely mad and set about pulling the turbo, to check for evidence of any contact between the turbine fins and the housing. Apparently normal both sides, no sign of any problems.



My intent was to pull the turbo and send it back for a replacement but to my untrained eye it was a-okay.

Sooooooooooo.....

I set about re-fitting it.



I found the strangest chuffing thing. Not sure what to make of it.

I unscrewed the two metal pipes that run along the head cover above the turbo, then something attached to one of the pipes dropped behind the engine.....wtf?

Looked and it was what I think is the EGR valve (not checked what it is yet), it's supposed to be mounted on a flange at the back of the engine with two small bolts.......mine was just sitting on the flange pretending!!!! No bolts - only held in place by the metal pipes screwed to the head cover.

So I hunted down two appropriate bolts and fastened it down to the flange as it should have been.

No idea if that could cause the noise I'm hearing and trying to fix.

Makes sense that it could have been disturbed during removal of the exhaust downpipe and cat whilst hunting for an exhaust leak, which I eventually found and repaired.

The vacuum line which runs from the valve to the intake manifold is pretty rough and certainly could have been leaking so I trimmed the end off of it and re-fitted it.

Then, while buttoning up the turbo I removed the DV to see if there was any problem with it. OOOOOOOFFFFTT!
Choked full of oil and clumps of sludgy stuff.

Cleaned it out thoroughly so should now work a tad better.

Lastly, I'm not convinced the vacuum line to the wastegate actuator was on properly as it was a pita to get back on with the original press clamp thingy.

It's now secure for sure.


So, to recap:

Pulled exhaust to turbo gasket - no change.
Pulled turbo - no visible problems, no real play in the shaft.
mounted EGR valve or whatever it is, some previous owner/mechanic forgot to bolt it in place (duuuuuuuuumb).
repaired EGR valve vacuum pipe.
Checked all hoses and connections to turbo and intercooler, all seem to be good and tight.
Cleaned out DV.

I can't check if any of these solved the noise problem until tomorrow evening, car is currently without coolant or oil.

Rough days' work that was but at least it's all back together and I'm not sending my turbo back (yet anyway lol)

I'm sure I'll still be swearing and pulling hair out tomorrow. That's just the way it is - to quote 2pac

Think I'll replace all the vacuum hoses when I fit the EBC, just as well my n75 has signs of green oxidation and a couple small cracks in it. Probably not helping matters....

 

Quick search just confirmed that is indeed the EGR valve - which was definitely not sealed.

Fingers crossed.

 

Faulty EGR (Kombi/combi valves as Audi likes to call them) can actually sound like an exhaust leak that's coming from the flex pipe in the exhaust on the 1.8. One thing to also take note is that if you've secured the kombi manifold bracket to the head and still notice a exhaust leak / strange sound, I would suspect the person before you didn't put the gasket in between the valve and the manifold so at higher RPMs it'll still leak out causing a weird noise. It might also be possible that the manifold itself could be broken if the engine was pushed into the firewall from an unreported accident.

They are generally a pain to work with, but very doable on the 1.8 - the larger motors are nightmares that require a lot of patience.

 

I just bolted it down sans gasket as there wasn't a gasket there.

It was a pita to do as the bolts go in from underneath and little or no room to get at them (what's new lol), figure they may have worked themselves loose over time, rather than someone forgetting to replace them.

On that note it's a good find anyway, I'm sure this could happen to someone out of the blue, they start hearing a crazy ripping noise all of a sudden but nothing seems out of place. If it hadn't fallen off the flange I may never have spotted it!

I will deal with it more permanently when I replace vacuum hoses next week.

It may be worth going over the engine with a fine-toothed comb so to speak.

After all it has done about 140k and has sat for nearly a year doing nowt.

Small niggles, still happy to have it running again, even if it aint perfect.

will find out later tonight if anything has changed after pulling the turbo etc yesterday.

 

SOLVED!!!

Was the EGR valve

No more noise.
I guess I disturbed it removing the downpipe and cat.

proper job!