Turbo sounds like a supercharger
 

Hi all

Yesturday my STI 6 started to whine and has got progressily worse, its deffo turbo or turbo related as the whine ramps with boost then holds pitch/level with boost pressure. I was hoping it may be just a boost leak so i pressurised the intake with 2 bar and used some soapy water on all joints and vacuum pipes without finding anything. It still holds the same vacuum at idle as before the problem. Car drives fine and seems to pull the same as before, but obiously not driving hard until solved.

I know no-one can diagnose a problem like this without seeing the car, just looking for some suggestions, hopefully not the turbo itself at fault.

Thanks

De cat?, slight exhaust blow?

could be an impact on one of the impellars which has changed the angle of the blade which inturn changes the noise created.

It has decat, full H+S 3-2.5" exhaust, H+S Up-pipe / downpipe, H+S manifolds.

Next step is to get it on the ramp and check for signs of a blown exhaust gasket somewhere, although it really doesnt sound like an exhaust blow ( exept maybe up-pipe )

Its really quite loud, but holds volume and pitch at full boost - ie doesnt increase with RPM but with boost.

I have a decat down pipe on mine, with a very slight exhaust blow, at the turbo/downpipe gasket and it whistles like mad! Can't hear a blow at all. Worth a look mate.

Sorry for a slight thread hijack, but how do you pressurise pipework to 2 bar? I would have thought the pressure would leak past the turbo and backwards through the air filter.

Air compressor connected to vac pipe and set to 2 bar.

Hold throttle open to pressurise cooler pipework/ cooler.

You can also block off the air filter pipe if needed.

Will do mate, thanks.

Interestingly i had no whine when the whole intake system was pressurised, kinda ruling out a noise caused by pinhole boost leak. Will make an adaptor and pressurise exhaust at the tailpipe tomorrow. Failing that, turbo off for inspection i think....

So you keep the compressor running I guess? Sorry for being dumb, just that I'm trying to locate a boost leak too.

FWIW, when I had an up-pipe gasket I was convinced I had a major engine fault, or a knackered turbo. It didn't whistle but didn't sound like a gasket gone either...not until it actually spat the remains out - then it sounded like a tractor :lol1:

So you keep the compressor running I guess? Sorry for being dumb, just that I'm trying to locate a boost leak too.

FWIW, when I had an up-pipe gasket go I was convinced I had a major engine fault, or a knackered turbo. It didn't whistle but didn't sound like a gasket gone either...not until it actually spat the remains out - then it sounded like a tractor :lol1:

Yeah, just leave it running. If you have a small reciever then the motor will be on and off all the time. I made an adapter from a 0-4bar regulator with some 4mm silicone hose on the exit, connected to the inlet manifold.

Easiest to check for exhaust leaks in the same way, will make a tapered bung tomorrow so i can plug the tailpipe, drill out the centre of the bung and fix some kind of air connector or something. This way the exhaust doesnt get hot and you can use the soapy water effectivly ( or leak detection fluid ).

You wouldn't get a noise when you pressurise the intake, your on the wrong side of the turbo, the whistling on mine is the turbo spooling, not a boost leak. For what is worth as well you may be better of testing with a hot exhaust, the expansion of metal can make a leak more prominent.

I pressurised the intake to rule out a boost leak not an exhaust leak.

With around 2 bar pressure in the exhaust, if there is a leak it will show ;)

Sorry my mistake I read your post wrong! What a div :) are you testing the exhaust in situe? Just out of interest are you open mouth down pipe?

Will test in situ, i havent had the DP off before so i dont know if its open mounth or not, why you ask??

Open mouths are renowned for noise but as it's a 'new' noise I doubt it's linked. I'm still sticking by exhaust leak tho, keep us posted mate. ;)

Deffo a new noise!! Will report back on Sunday, wont have a chance to look into it until then.

Thanks

Pressurised exhaust, found a leak from the DP-CP gasket, and a leak from one of the head-manifold gaskets.

I will order a full set of gaskets and replace all of them, and hopefully that will sort the problem.

Will report back end of the week once they have been replaced.

All gaskets replaced with genuine Subaru one ( £90 !! ), exhaust is still blowing from the slip joint on the manifold, dont really know what i can do about this? I may call down to my local exhaust fab place and see if they can increase the size of the inner joint so it seals better.

Still sounds like its supercharged and i have now noticed a slight drop in boost pressure and slightly less vacuum at idle. Will remove bumper and arch liners and pressure test ALL intercooler piperwork and vacuum lines. Must be a pinhole somewhere.

A common cause of turbo whine is a turbo with excessive shaft play to the extent that the turbine wheels are touching the housing. You can remove the turbo inlet pipe and try shaking the compressor wheel side to side to see how much play it has.