1985 cali 300D air hissing noise\blow off valve from pass side

[fang508]

I was driving around 80mph one day when I heard what sounded like a blowoff valve go off. It kinda sounded like what happens when you vent an air compressor. It was instant and rather loud but I didn't really notice any performance issues at the time so I kept driving. I've been driving it like this for a few days and the hissing sound has quieted down but it's still there. I have a feeling it is a boost leak but I don't know where to start diagnosing. The hissing noise starts happening around 1800rpm and progressively gets louder the higher the engine revs until about 3500rpm where it levels off. Research I have done suggests it could be a problem with the overboost protection circuit, wastegate stuck, or leaking turbo seals etc. Anybody else had something like this happen?

[vwnate1]

The turbo's wastegate has an open exhaust port under neath it, look up from below with a flashlight and you'll prolly see it, all oily ad it gets when the poppet valve sticks open....

Not terribly hard to take apart, force the stuck valve out and clean it well, consider hand lapping the valve and seat for vastly improved off idle performance and of course, you'll need a boost gauge to properly adjust it to 13 ~ 16" of boost pressure .

Don't get stupid over boosting it .

[fang508]

I tried taking the waste gate apart. The diaphragm locknut is seized. I also had a hard time getting a wrench on it because of the angle. There was oil in the waste gate but no where near as bad as others I've seen. I verified that the holes in the valve shaft are clear (blew compressed air and solvent through them) and I can move the valve in and out. The valve is a little hard to compress but it moves freely and springs back. I also cleaned the manifold banjo bolt and the bore it goes into as well as replace the dry rotted lines going to the over boost circuit. Hissing sound still there. Hooked up a boost gauge and got 10psi at wot. Now there was another issue which I thought I had fixed but now unsure. The flex line going to egr had split itself in the center. I had filled it in with jb weld which seems to be holding... Could that cause a hissing noise? I also sprayed soap water around a bunch of parts. Where the turbo connects to the intake manifold there is an air leak. Seems to create a slight vacuum (boost gauge shows slight vacuum) right before turbo engages and then bubbles out of the seal when the turbo slows back down when letting off throttle. It doesn't leak any other time...

[vwnate1]

Looks like you have your work cut out .

There should never be any vacuum, even at idle there should be a slight pressure .

The bubbles you see should be corrected and you should buy one of Rich's EGR blocking plates and install it .

Keep at it, you've found at least two issues that need fixing straight away .

? If you turn the turbo with your fingers, (engine off of course) does it spin freely ? .

I've only once discovered the problem of vacuum when first I toched the throttle, over hauled the turbo and cleaned out all the gunk and it stopped .

[Diseasel300]

The hissing is a boost leak. You've already found the source with your bubbles. Fix it and the hissing noise will go away.

As Nate said, there shouldn't be vacuum. The turbo should always be rolling if the engine is running, pressure in the manifold should be 0 or positive. Vacuum in the manifold suggests either the turbo is stuck, you have an obstruction somewhere in the inlet plumbing, or your air filter is catastrophically dirty.