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General Car Related Discussion.To discuss anything that is related to cars and automotive technology that doesnt naturally fit into another forum catagory.
question is that it's fine in the early gears however the problem only occurs in 4th, 5th and 6th?
the boost solenoid duty cycles the boost through the gears not always using the full sweep of the vnt ring insode, please remember the car has no wastegate, so nothing conventionally as what we know as boost control, in the higher gears the exhaust pressure is lower (lower revs) so the vnt unit needs to return back to a small opening but big enough not to restrict power, as the syste has no vent on the vaccum teh capsule for the vnt will not let the vaccum go back to the solenoid to be redirected.
another small issue, big black vac res on the engine, remove the cvac pipe and see if anyones super glued the tail back on, after breaking it trying to get the pipe off this gives negative boost control and no vaccuum under certain conditions for the vnt !