my friend has a blacktop SR20 everything is stock…couple weeks ago when he revs thier is a humming or rattling sound and the turbo is not fully boosting what should he do?
see if the turbo is loose from the manifold. VERY common!
or boost leak or vacuum leak.
best place to start.
where can the boost leak becoming from though?
Just check all couplers for cracks or looseness. The rubber might be dried out and split open. the bands might be loose, or broken. the plastic pipe going from intercooler too throttle body could have a crack in it.
the Vacuum lines might be dried out and cracked or loose, or missing
first i would check the turbo is tight. when engine is cold, start up and hold hand down around turbo flange where it meets the manifold, if you can feel hot air blowing through your fingers, that might be your problem. make sure you don’t confuse the air blowing through your engine bay from the rad fan as an exhaust leak though! CAREFUL, the turbo heats up VERY QUICKLY!!!
i am willing to bet that its that the turbo to maniold is loose, happened to me its a bitch because the only way you can tighten it is by taking the tubo and manifld off
or that the gasket from turbo to maniold is shot