Date: Sat, 13 Feb 1999 18:53:07 -0800
From: Justin VanAbrahams <jvanabranopsam.com>
Subject: Re: turbo problem '83 900T


Michael Oakes wrote: > > I have problems with low boost. If I had to make a guess, I'd say it's your fuel system. Check fuel pressure, and make sure the fuel filter has been replaced within the last 50k or so. It sounds like you may be getting excessive knock (from a lean mixture) and the APC system is knocking back boost. I had a similar problem in my '84 900T and my '88 900T. After that, check your distributor to make sure it's advancing properly. Also check for exhaust leaks - these aere symptoms you might see. If you run out of ideas, try removing the vacuum line from the APC solenoid to the turbo's wastegate and drive around for a bit. You should gets TONS of boost. DO NOT DRIVE AROUND LIKE THIS FOR ANY PERIOD OF TIME OR YOU COULD SERIOUSLY HURT YOUR ENGINE OR TURBO. If you don't, you've either got: a) a damaged or tired turbo (unlikely) b) a damaged wastegate (relatively likely) c) a damaged or cracked exhaust manifold (possible) d) a serious problem with the engine that's causing it to product insufficient exhaust to spin the turbo (unlikely, but could be compression related) To virtually (but not 100%) rule out #1, pull the elbow off the turbo and take a look at the turbine wheel. Make sure the vanes aren't broken or bent, and that the turbo housing itself isn't cracked. Spin it gently with your hand to make sure it spins fairly easily, and jiggle it GENTLY to make sure there isn't excessive play. If it doesn't spin with minimal force or there's excessive play, you probably need a new turbo. To rule out #2, disconnect the wastegate from the actuator and see if you can spin the actuator rod. Don't try too hard, or you could accidentially rip the diaphragm yourself. If it spins easily, there's a good chance you've got a leaky wastegate. There may be other ways to check it as well, but I am not aware of any. To rule out #3, have it checked. It's also relatively likely on such an old car and might only surface once the manifold is very warm and has expanded, opening any small cracks. If you pull it off, you could check to be sure the gasket there isn't damaged - if it is, you may have a stretched stud or a warped manifold, either of which could lead to an improper seal and thus an exhaust leak. #4 is a bitch :) and pretty unlikely if the car itself runs okay and gets expected mileage. Before you get into that, though, have the fuel pressure tested and your distributor checked for proper advance. Then have your exhaust system inspected for leaks. Good luck, -Justin

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