[Mk2] [Turbo] car not boosting properly

[skyline]

my mates car aint boosting properly it has an mbc fitted and when fully closed it boosts 0.5 bar but when he brought it down to me the top of thembc had fallen of so was fully opened and yet it was still only boosting 0.8 bar when surley it should have kept boosting til either the turbo or engine blew
i have fitted another mbc and unplugged the vsv but still it only boosts 0.5 when closed and 0.8 when fully opened
any suggestion as to what the problem is

[PW@Woodsport]

faulty turbo,boost leak,faulty bov,wastegate stuck or partially open,actuator faulty....theres quite a few things that could be wrong.

[skyline]

turbo and actuator have been changed so that leaves the bov or a boost leak
whats the best way to check for boost leak
any others t check or rule out

[PW@Woodsport]

take the turbo outlet pipe off and attach a makeshift pipe that runs straight from the turbo to the throttle body,if it still isnt boosting then theres a problem with the turbo or wastegate.If it boosts fine then theres a problem with BOV or IC piping or IC.

Are you sure the actuator arm is attached to the wastegate ok? they often come adrift

[skyline]

i will check the actuator but it shouldnt be the problem cause he had the turbo and actuator changed cause thats wat he was told was why the car was boosting low

i have a feeling its the bov cause it can be rotated easily and has a little play in it but he said ot was like that on his old mr2 but i told him to change it anyway to rule it out

[skyline]

i have now changed the bov to the standard 1 and still only goes up to 0.8bar with mbc open 2 full.its gota b the intercooler ???? dont kno what else 2 say 2 him any ideas lads???

[Slarty]

It could (longish shot) also be the CAT or the exhaust has collapsed, not allowing the turbo to spin up fully. Worth checking I guess

[mr2neil]

the mbc doesnt allow more boost, it restricts the boost gettin to the actuator, so if the top was off, its not doin nothing, then when actuator gets its limit it will open and the boost will level off.(at normal boost-ie if u had no mbc fitted)
by tightening the mbc u are restricting the pressurized air from gettin to the actuator at all, so when the boost gets high enough to get thru the mbc, its gonna be more than high enough for actuator, which will then operate!!