Sounds like a most definite boost leak, you said it was smoking out the tail pipe?

 

once in a blue moon, at idle. it's a 20 year old motor. i just saw it once and freaked out instantly.

 

turns out the boost controller was installed WAY wrong, so i fixed that. it builds up to 4psi now, but it still tapers off, i can't find the boost leak and no one around here knows anything about the car, nor will they touch it.

 

Ok, so it's drawing vacuum at boost. That means that it has some restriction to getting air, and has to be caused by something inline with the air going into the engine. So what things can choke off the flow to the engine? The only thing it could possibly be is the turbo. Have you tried disconnecting the turbo piping and seeing what happens? That would get rid of a lot of variables really fast. You may have to relocate the MAF temporarily if you use one.

You might have a seized wastegate or something like that, or the boost controller is faulty. I'm assuming there is a reasonably conservative spring in the wastegate, so you might want to remove and bypass the boost controller and see what happens.

Where is the actual control line for the wastegate attached? If it's attached to the manifold, you might have ruptured the wastegate diaphragm under vacuum.

 

This.

 

I'm still trying to figure out in my head if another type of engine problem (fuel, spark, etc) could lower the exhaust flow enough to stall the turbo and create manifold vacuum at WOT.

 

first off, thanks a lot for the input.

if by control line for the wastegate you mean a vacuum line, it's attached to the boost controller and the other side of the boost controller is connected to the intake side of the turbo. this is the way every diagram said to do it with an internally gated turbo.

as for the boost controller not working, at first the boost controller was routed to where it literally did nothing. it was actually picking up pressure AFTER the wastegate so i was held up at 6psi (6psi spring) no matter how much i adjusted it. so now i have the controller routed to where it will pick up first, then when it maxes out, report to the wastegate to open, i suppose? and the problem occurred before the boost controller was re-routed. so basically it pretty much HAS to be the turbo? or a hella bad boost leak maybe?

this is my first turbo car really, i'm still trying to learn the ropes.

 

I'd say cut to the chase and yank the turbo. Once it's off the car, it's easy to check the wastegate for proper function just by hand. I would really get rid of the boost controller though, just to take it out of the equation.

 

alright, hopefully i can find the time soon to do this.

 

oh my.