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I have an '89 745T with a Mitsubishi TD-05 turbo. About a week ago I lost all boost which is manifested in being able to slowly and deliberately cruise up to normal driving speeds be it in town or on the highway, but when the boost gauge approaches the yellow band, it barely crosses into it and there is no noticeable turbo response. There does appear to be a sound like an air leak or something similar that increases in intensity the higher you go in rpms and the more you force the boost gauge into the yellow. The shaft of the turbo seems to have very little side to side play(lateral?) (no more than 1/16" either way), with almost no noticeable forward/back play (axial?). Also the turbine spins freely with no indication of contacting the sides of the housing. On the advice of a mechanic I used a vacuum gauge to test the relief valve on the front of the turbo. Applying vacuum actuates the valve (you can hear it click), and it holds vacuum. Also, applying suction to the same valve seemed to hold as well, but I don't know if that means anything. I also disconnected the hose running out of the housing to the waste gate and applied vacuum here as well. It held vacuum and when I applied force (opposite of vacuum) it also seemed to hold. However, when using the vacuum pump on the waste gate hose I cannot tell if it actuates the waste gate. Can you even force the waste gate to move by applying vacuum to it? I got underneath the car and was able to move the waste gate manually by grabbing it with pliers and moving it open and closed, but still, the car runs like it only has 50 hp or something. It will go up to 80 mph and can be held there but there is simply no boost. Any suggestions on how to narrow down this problem? If it comes down to it this mechanic can maybe get me a used turbo and install it for $300 for the turbo and $300 labor. The TD-05 that's on the car now was also a used unit - not rebuilt. Otherwise, he drove the car and said he thought the engine was mechanically sound and that he felt it had to be a turbo problem. Any suggestions?
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