Diagnosing Turbo Wastegate and Bypass valve Troubles

[jzmuda]

This post: https://www.matthewsvolvosite.com/forums ... =1&t=20243, regarding my turbo boost fluctuating dramatically, did not generate a solution. So, I thought I'd try again.

In my 1994 850 Turbo, if I pin the throttle, it will build full boost. As soon as it reaches full boost however, it drops to near atmospheric. From there, it continues to build to full boost and then drops off again.

It has been suggested that this might simply be a leak. I've looked around and not found anything, I have sprayed carb cleaner around all the connections and observe no change in engine speed.

I can't imagine how a simple leak in the system could cause this. I've had leaks before and they simply resulted in not building full boost, or taking a long time to do so. This is a pretty rapid fluctuation, say 1 hz.

Is there a way to check the bypass valve and the waste-gate?

Any help would be much appreciated.

Thanks,

Jay

[zoomungus]

I had a similar problem so I took out the recirc valve and replaced i t with a forge blanking plate plus a bailey dump valve, now its holding boost but the boost pressure is not as high as it should be, on my old 855 it was around 16 psi and off the scale on the boost gauge, so im thinking that maybe the waste gate is opening too early, im going to adjust the play on the gate.

[osman]

Im having similar turbo issues. Feels like my wastegate is opening early. What was your problem/solution?