Nick Christopher

Brain picking time. 09 cobalt ss stock other than mishimoto fmic. Pretty loud noise under heavy boost. Thought I had shaft play but that's not the case. No shavings in oil or the slight amount of oil on intake side of turbo.Sometimes at low rpms it it falls on its face and also when I powershift from first to second it falls on its face then it'll pick up after a second or two. Sometimes it idle funny like it drops then catches itself and hear lately its been popping and cracking on rpm down stroke. And EVERY single time I shut it off now after the motor has stopped I get a little putt out the exhaust. Any ideas or inputs or other people who have resolved this issue. Thanks in advance please help

blackbird

When you say loud noise under boost, is it sustained noise or a single event? Can you describe what it sounds like a little better?

Any codes set? Popping sounds in exhaust, run-on after shutting engine off and odd power behavior would have me first suspecting a fuel or vacuum harness issue.

63 Nova SS

iTrader: (3)

I'm wondering if it's injector seals, or something like that, but that should effect it running on.
Is the car tuned? What has are you running? And as blackbird requested- what does it sound like?

Nick Christopher

Sorry guys hadn't checked back. The car is bone stock other than new mishimoto fmic. Yes it does pop and backfire at times. Also fuel cuts when under boost between 4 and 5 k rpm. The best way to describe the sound is very thin metal making contact with something. I have only run 93 thru it since I bought it. Has an auto part store maf and replaced plugs with ac delcos. Recently I put octane booster in it and it ran good still had the noise tho but now when I get into boost in 3rd _5th if I hold it in boost for more than 5 seconds after hitting at least 10 psi I lose all boost pressure other than 2 or 3 psi and the car has absolutely no power.

coolbalt1

Does it sound like a boxer engine by any chance? Could be a bad lifter

blackbird

When holding it and the boost drops, is the check engine light or "reduced power" warning showing in the instrument cluster? With the extra info it sounds like a fueling, sensor or vacuum problem. If you have access to a scan tool it would be interesting to data log and see if something is way off. Besides a very good visual inspection that might be the easiest way to try to pinpoint why it's running wrong which may very well be related to the noise.

Nick Christopher

No cel until yesterday. Po299 turbocharger a under boost condition. it did show engine power reduced one time but it was before all the new issues started. Its odd because when the boost falls off I can hit the clutch turn it off then back on and start it and it does what its supposed to do until under heavy boost. I did just discover that it will no longer hit 13 or 14 psi. More so 8 to 11 psi then slowly drops for about two seconds then straight down to 2 psi and no power. The noise is also worst now. Would I be able to hear a diffrence if my wastegate is stuck open. Is there any way I can upload a video so you guys can hear what I'm talking about?

blackbird

That really sounds like it could be caused by the compressor bypass/diverter/surge valve (i.e. blow-off valve (BOV)). If it isn't sealing you'd leak boost pressure from the outlet side of the turbo compressor back to the inlet, would see fluctuating or low boost, and it would very likely make a lot of noise back out through the intake tract.

I'm trying to go off memory here, but I recall it bolts on the turbo and should have a fitting for a vacuum line that goes to the control solenoid. You could temporarily run a vacuum line from an intake manifold for a constant boost reference source to see if there's any change. If the solenoid is working correctly and the internal diaphragm valve is broke or leaking it might not make any difference.

I'm also not near my factory shop manuals to see if there's a test procedure. You could probably pull it off and take a close visual inspection to see if it shows and tears or damage tot he diaphragm.

Nick Christopher

Finally! This is extremely helpful. Finally I'm pointed in some kind of direction of where to begin. Th so much will update when I get off work to see if I can figure it out