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wheezing noise & boost problem
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Posted by Mark McCrea [Email] (more from Mark McCrea) on Sat, 12 Jun 2004 16:51:22 Share Post by Email
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Car: 1989 900T 16s with modified APC.

Recently I have noticed that the overboost which used to go to 24psi (near the end of the red) at 3000rpm in 3rd barely make it to 14psi (the red). However, as the revs build you begin to get a wheezing noise like an air leak and the boost builds to around 18psi at 5-6000 rpm like I always get. What I'm saying is that the boost builds slowly with the revs where I used to get an overboost to the end of the red, a kick in the back and off it went. These last two weeks I have pressure tested every auxiliary (dump valve, fuel regulator, vent controls, distributor etc) and found nothing. Over the last few days I have removed the head, had the valves reseated, had the turbo fitted with a new bearing and new gaskets all round. Checked that the solenoid valve chatters when it passes 7psi, the apc does seem to be controlling the boost at higher revs, base boost still at 0.5 bar.

Tonight I disconnected the pipe from the solenoid valve to the actuator to get full boost. The boost still takes too long to build but will pink once it gets to a high enough pressure. To me this proves the problem is not APC or electrical related.

A hint, which I don't want everyone to jump on if they can think of any other reasons, is that the exhaust has a rattle. I've tightened all the clamps and been under the car while an assistant revs the engine and the noise comes from inside the main silencer.

I am inclined to think that the exhaust, which is stainless steel 2.25 inch (and has been there for 7 years), might have a fractured internal pipe and some of the silencer material is blocking the exhaust.

Has anyone come across this before or can anyone think of another reason??

posted by 195.92.168...

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