whip

Cruising along in 4th this morning while the car was still warming up, I noticed a high-pitched whistling noise. It would only do it at a certain rpm (2600) and seemed to go once the engine warmed. I could only hear it with the window open, but I swear it was the same noise that I can hear when letting the scoob cool down after each drive. At idle the noise stops and starts pretty regularly. It doesn't sound like the blowing over a bottle noise though, more like a constant high-ish tone which doesn't vary with engine rpm.

Anyone got any ideas?

TonyNesta

Does it sound like this.....http://bbs.scoobynet.co.uk/Forum9/HTML/002887.html ???????

whip

Nope m8, it was doin it on a constant throttle rather than under accelleration. I'll try to recreate it on the way home tonight, as it only seems to do it on a cold engine.

Does your whistle vary in pitch depending on turbo rpm? Mine was a continuous pitch.

TonyNesta

Mine is also a continuous pitch, like someone blowing a whistle when the turbo spins up.

whip

Got the same noise again on the way home last night. It doesn't seem to be rpm related in any way, as I would reach 38mph (in a 40 zone occifer ) at which point the whine would start, then I could drop the clutch/change to 5th or whatever and it would still do it. After that its hard to hear due to wind noise/buffeting.

The noise is most apparent when I stop after a drive where the car's been fully warmed, and seems to be louder depending on how hard it's been driven. Last night after a B-road blast I let the car idle for a while and tried to locate it, it definitely seems to be coming from around the turbo. It's also intermittent at idle, and will stop/start periodically.

In every respect the car seems fine though, just curious as to what the noise is. Having not driven any other impreza's I can't say whether mine's down on power though and it's done this since I bought it (MY00, had 14500k now on 16500k).

My short-term solution is to turn the stereo up.

Whip

Pete Croney

Its when the manifold pressure just starts to open/close the dump valve. The air rushes through the reduced gap and makes a whistling sound.

johnfelstead

It shouldnt do it on idle (unless your idle control is poor and the revs are rising and falling constantly). The spring is there to keep the valve closed when there is no presure diferential between inlet to the turbo and plenum chamber. On idle the presures should be equal.

Sounds like you may have a week spring in the dump valve of it is contaminated with oil and sticking slightly.

You do get some flow through the valve when transitioning from boost to vacuum which occurs when driving on a light constant throttle as your inputs are always slightly changing and causing the presures to change.

The thing that could damage the turbo is if the dump valve doesnt close fully on boost, that causes the turbo to overspeed.

I dont think you have that problem so should be OK for now, but if your not sure get it checked out.

whip

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR><B>If it didnt do it before maybe your dump valve is starting to fail.[/quote]



<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR><B>how many miles has the car done? The spring may be getting a bit tired in the dump valve. It may be a bit bunged up with oil residue?[/quote]

Mine's now on 16500, had the car for 2000 miles and it's always done it on idle after a good drive. Is it easy to check or should I just wait til the next service (january)?

I'm new to turbo'd engines, is this likely to cause any damage or will it just result in the dump valve staying slightly open most of the time (which I assume would give a slight power-loss)?

johnfelstead

damn, beat me too it pete.

If it didnt do it before maybe your dump valve is starting to fail.

how many miles has the car done? The spring may be getting a bit tired in the dump valve. It may be a bit bunged up with oil residue?

TonyNesta

So would that explain my 'whistle' as well ?

whip

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR><B>It shouldnt do it on idle (unless your idle control is poor and the revs are rising and falling constantly).[/quote]

It settles at around 700rpm, haven't really noticed it idling unevenly though (my last car was a 205gti - idle, what idle? )

Is it significant that it doesn't seem to do it when the engine's cold? Is it an easy task to check the spring? If so, any chance of some destruct...err..INSTRUCTions

Your help's much appreciated John.

whip
"where's me dump valve"

johnfelstead

sorry, not thinking straight right now.

you will actually have a slight vacumm in the plenum on tickover, the presures will be diferent.

Thats one of the reasons there is a spring in the BOV, to give resistence to idle vacumm.

I am not sure how easy it is to strip a standard BOV. I am sure there are people on here that can tell you. It does sound to me like its going a bit duff. There is some history of duff BOV's on Imprezas.

whip

I noticed last night, after tackling a b-road at higher revs than usual (ie between 5 and 7k) that it didn't whistle afterwards on tickover. Maybe the higher pressures freed it up a bit or something, I'm not sure on the exact mechanics of a BOV tho.


This morning it's doin it again.

Not sure where to go from here, I suspect a dealer will try to fob me off but I'll give it a shot anyhow.

Cheers John.

[This message has been edited by whip (edited 25 August 2001).]

Sul

John,

im no expert but.....

I was having various noises, so I took bits off left right and centre.

The DV is very easy to remove, to bolts and two hoses to remove. Get yourself a pair of pliers and a 12mm spanner.

With the bolts out, the DV lifts off, and you can see how it works. Not a very advanced bit of kit. Just a plunger on a spring seperating two chambers.

if nothing else, it'll help you understand whats going on.

BTW dont worry - there are no bits to "boing or twang" as you remove it.

Mark

Oh yeah - I also get whistling, but i traced it the drivers side mirror surround. Air flow makes it whistle. But under acceleration i cant hear, cos of the engine noise.

Im pretty sure this wont help you though.



[This message has been edited by Sul (edited 26 August 2001).]

dowser

On a my99 I had very lumpy response on a light throttle.

Took the dump-valve off to find it very stiff due to oil contamination.

Cleaned it up, all OK

Took the one off my new my00 (at 30k kms) to see if it was suffering similar - operates smooth as a baby's bum.....go figure.

Easy to remove - just be careful of those i/c fins

Richard

whip

Took the BOV off yesterday and checked it out, seems fine. Operates smoothly and it wasn't dirty. I cleaned up the edges of the little piston where it makes a seal just to see if that made a difference, refitted it and fired her up - still makes the whistling noise.