Thread: boost bleed off
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beepbeep beepbeep is offline
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Join Date: Jun 2001
Location: Sweden
Posts: 5,682
See the hose 17 going into turbos intake? That's the hose you should jam the cylinder into and pressurize. You loosen the clamp 17 that sit's on the other side of the hose (hose should still be attached to turbo on the other side), remove pipe 16, jam the cylinder into hose and tighten it again with the clamp. Then you pump up wholw sheebang to 0.8 bar and listen for hissing noises. That way you can pressurize the system from turbo upwards.

It will pressurize the turbo, intercooler, intermediate plenum and plenum going into the heads. Only way for air to escape is trough heads and exhaust valves. Your cam aren't radical enough to have overlap (I hope). There will be some air leaking past the valve seats and their stems but you should be able to pinpoint any external leaks. If your leak is bad enough to make boost taper a lot, you will be able to hear it. I never did this to 911 but I did it on couple of other turbocharged cars and principle is equal:

You pressurize the system (just like turbo would when on boost) but with engine not moving. Then you listen for leaks. Just be careful with pressure and don't go past what typical turbo would do (0.8 bar is safe). We get heaps of SAAB's that we troubleshoot this way. Two months ago I had a very annoying whooshing sound coming from my Audi S4 and just couldn't find the damn leak. Pressurized everything to 0.8 bar and still couldn't find it albeit it was obvious that air was leaking somewhere. Went with my hands across all plumbing and finally found air escaping trough two cracks on the armored rubber hose on intercooler intake.

I would bet 50 öre that your intercooler O-rings aren't sealing. Check those first.

Thank you for your time,

Last edited by beepbeep; 12-17-2007 at 02:26 PM..
Old 12-17-2007, 02:15 PM
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