I brought my recently acquired '96 993tt in to the dealer to replace a faulty slave cylinder and pressure control valve. I also asked them to check the boost/boost gauge as I wasn't getting over .6 bar boost and at times was showing .2 bar at idle.

Per the dealer, all checked ok. Gauge registered up to .8 bar during thier road test with no other anomalies. After warming up the car on the drive home, I put my foot in it to double check the boost gauge. What I got was a new and unusual noise that grew in intensity as the boost built up. It was a metallic brushing sound. Imagine a stiff bristled brush on the inside of a metal garbage can. Needless to say, my test ended abruptly as I didn't want to inflict more damage if something was truly wrong. I babied the car the rest of the way home.

Any ideas what this might be? Was looking to tkae the car out for a spirited drive this weekend, but will now have to postpone until I can get her back to the dealer.

Appreciate any input form all the turbo experts out there.

Thanks,

kevin

 

Kevin,

Couple of thoughts here, was it a winded type noise. Possiable intake leak from a split hose? How the diverter valves. If it really is a metal to metal noise under boost this sounds as if it could be a bad turbo. If that is the case I would stop driving it at all. If the impeller comes apart you will have real problems. How many miles are on the car?

 

Hopefully, it might just need an alternator pulley update like my 96tt. I was thinking the worse too when I heard that metallic sound and smell. Rick and Robin (993tt.com and p-car.com) were very helpful. What you're describing is quite similar to my experience except I had no problems with the boost guage. Hope this helps. Good luck.

Vince

 

Kevin,

Vince may be onto something, in that your two problems (faulty boost reading, and metallic noise) may be unrelated. Of course, it could be an impeller, as well.

The reason I say this is because the faulty baseline 0.2 bar reading is a common problem that has been discussed previously on this forum. As I understand it, it can sometimes be related to a faulty boost sensor. I've experienced it intermittently in the past, and actually have a new boost sensor that I plan to install soon.

I've also experienced problems with a metallic noise associated with the two alternator pulley halves vibrating against each other (worse, of course, on acceleration) after having the pulley update done and belts changed. Unfortunately, the dealer had stripped the alternator shaft bolt, allowing the pulley halves to drift. I should have done the work myself.

Good luck with the detective work. You might want to take Stephen's advice and not drive the car until you make sure it's not a problem with the turbos themselves.

 

I've had the privilege of breaking 2 alternator belts while driving. Once in my car and once in another. When it happens, it sounds like you ran over something metal, then a big puff of white smoke usually comes out the back.

Do a quick check of your belts. There should be three. And check them for tightness as well.

Are there any other warning lights on your dash?

 

I'm not all that familiar with turbos, but had look anyway in case there was anything obviously out of place.

What I did find was that the dealer must have removed the intercooler as the rubber pipe on the left side did not get reseated properly before tha clamp was tightened. Loosened the clamp, coaxed the rubber pipe on fully and tightened back up.

Took a careful test drive and all seems ok. Guess the 'metallic brushing" sound was rushing air around an air leak. Boy do I feel like the boy who cried wolf.

Anyway, thanks for taking the time to respond to my unfounded panic.

Kevin

 

I'm glad all is well. Don't mean to burst your bubble but my metallic noise did come and go at first. Just trying to help avoid surprises for you if you do hear the sound again. Hopefully that was all it really was and you have fixed the problem by tightening the hose. Enjoy your ride. <img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

Vince