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Quinn,
Recall that in your last post I was surprised that you could reach that boost pressure with stock CIS. I had the EXACT same conditions with my car and it was a lack of fuel that caused it. I had to upgrade fuel flow and the problem went away (moved it to a higher a boost pressure). Although this isn't super technical it is my guess as to what is happening. An engine generally has an RPM range at which it most effectively breathes. This changes depending on cams and other factors. In this case the engine is likely drawing more air at 3000-4000 level b/c this is where the engine can most effectively breath. Thus this is where you are leaning out. Does the engine feel momentarily sluggish before you start having sputtering? When your mix gets lean enough it will get hotter and cause detonation. This is what you are seeing with the sputtering and chugs of smoke. Does the engine make an abnormal pop sound when this happens?
Not sure how long you have had this setup but often when ambient air temps drop (in the fall/winter) your turbo and engine will behave differently b/c the air is more dense. Have you run this setup in colder temps before? From my experience, problems tended to show their ugly head about right now. I was fine in the summer.
Sorry for getting longwinded. I believe to fix your problem you will either need to upgrade your fuel system or lower your boost. In the meantime take it easy on the car b/c detonation will eat your engine PDQ.
It seems that if you were having an ignition problem, symptoms would not be in one engine loading condition. You would probably be experiencing symptoms across the board.
Anyway, hope this helps and good luck getting it sorted out. Keep us posted on what you find.
David
79 900T
posted by 129.59.24...
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