Boost Whine?

[ian2000t]

I've got an annoying whine on boost (comes in about 5psi). It's not like a normal turbo whistle - I have that aswell which is fine.

This sounds more like someone actually whistling, like a boost leak. It's been like it since I did the headgasket which is probably knocking on for 12 months ago now.

Since then I've had every peice of boost hose on and off, and when refitting have refitted them very carefully so they don't leak. So, I assumed it was the inlet gasket.

Well, yesterday I finished fitting the N/A manifold, carefully fitting it with gasket goo and letting that go off properly before driving it. But the whine is still there. When I did the inlet manifold I found a couple of exhaust manifold studs were not fully tight so tightened them up.

Any other thoughts what it could be? Could it be the turbo itself? Such an awkward thing to find, as you can't get boost on the driveway!

[v8volvo]

I would start by checking all your EGR connections for any leakage. Generally any leak large enough to make whistling noises will also leave soot marks around where it is leaking. Turbo drive pressure in the exhaust manifold and EGR system is always at least as high as intake boost pressure so can make lots of noise when a leak occurs. EGR valve itself could also be faulty but I have never seen it myself. Many times on TDI's and D24T's I have found big nasty boost whistles coming from EGR joint leaks though.

George

[ian2000t]

Don't have an EGR system on mine. Don't think it ever did from factory either. The bit of the inlet manifold that it feeds into normally is just a blank cast on mine (my D24TIC manifold...before I just swapped it for N/A).

Interesting... Maybe exhaust manifold leaking? It's done it since HG change, so that's possible if I didn't tightened it up enough. Have retightened them now but perhaps gasket is sooty and not sealing properly? Pulls ok but turbo doesn't feel like it spools early enough.

[v8volvo]

Interesting. I always thought all the factory TIC motors had EGR. At least all the pictures of them I have seen have had it. Of course I have never seen one in person and don't have any firsthand knowledge of their variations. Here in the US, all D24T's from 1985 onward had EGR.

In any case it is nice that you don't have EGR -- that's one less thing to have a problem with. Given the type of noise you describe I doubt that your leak is at one of the exhaust ports, since those usually make a rhythmic whapping noise when they leak. However, any other exhaust joint ahead of the turbo could be a place to look at. Are the 4 nuts that secure the compressor housing to the exhaust manifold-turbo flange tight? Did you use a sheetmetal gasket at the manifold-to-turbo joint, or no gasket? I have found them both with and without gaskets. The only one I have recently reassembled, I did not use a gasket and it did not leak. Maybe they are better off without. If you did use a gasket, then I would check that joint carefully. Look for signs of soot leakage around where the flanges meet.

Have you checked your intercooler core and end tanks? Those can crack and leak sometimes as well, and may be hard to find since it may be a small crack that only opens up when the intercooler expands under boost. If you don't find anything obvious on the exhaust side, you could try getting a chunk of PVC or some other way of temporarily bypassing the intercooler to eliminate it from the charge air circuit, and see if the noise goes away.

[ian2000t]

Well, to be honest with you I thought they were all EGR'd aswell, definitely all 940s I have seen are. Mine is an earlier model though...760 facelift (pre-940). Will stick some pics up!

Good point about exhaust manifold noise. Will check the turbo connection, but that's something I've never dismantled on mine. Also, will try eliminating the intercooler...sods law says its probably that lol!

[michaelovitch]

You can make boost by reving it up steady and spray soapy water to check.
easy and quick.

If you installed the new manifold and the noise is still here that mean it's upstream that part of the circuit.

remove the inlet hose of the intake and make boost.

a boost leak will desappear. (you will not can build pressure in the circuit)
a mechanical or a vacuum noise will stay.

I 've had a very acute whistling on my naturally aspirated engine wich was caused by a glowplug not enough tightened.

you can have this problem too maybe but i doubt.
you have a shit load of pressure yet even without boost.

[ian2000t]

Here is some pics of my EGR'less D24Tic. Sorry bad quality they are all I have. But you can see there is no pipe coming from exhaust, and also no pipe going the the inlet (normally just before the boost pipe).
http://i103.photobucket.com/albums/m...7012011050.jpg
http://i103.photobucket.com/albums/m...7012011051.jpg
http://i103.photobucket.com/albums/m...7012011052.jpg

Here's my new N/A Manifold:
http://i103.photobucket.com/albums/m...o/IMAG0192.jpg
http://i103.photobucket.com/albums/m...o/IMAG0193.jpg

[ian2000t]

Originally Posted by michaelovitch

You can make boost by reving it up steady and spray soapy water to check.
easy and quick.

I don't think i will make enough boost on the driveway - only really whines after 5 psi, which I don't think I can reach without it being under decent load.