Not boosting properly after turbo rebuild

[Dangerous Dave]

As the title says, recently rebuilt my turbo, and since refitting it, the turbo won't boost above 7-8 psi. Its the LPT turbo, and as standard boosts to 5-6psi. I have an mbc fitted, and before the rebuild it was boosting to 10-11psi. It also seems to take ages to spool up, and its louder than it was before, but I'm putting this down to the new seals and bearings.

Is there a wear-in period?

Just want a list of things to look for (obviously I've already checked all the pipes for leaks). Could it be the wastegate? I've had the CBV off and checked that too, but it seems to be ok.

Cheers

Bomb

[Alan M]

If it was assembled correctly it should be no different to before. It could be that a snap ring or throw washer is in wrong causing a problem. Was it free to spin after reassembly?

[Dangerous Dave]

Yeah, wasn't tight or anything, as far as I can remember it spun the same as it did before the rebuild but without the play in the bearings. And I didn't touch the wastegate arm, so it can't have moved.

I'm gonna have to give it a going over when the temperatures frop, as its too hot to be working round a hot engine bay at the moment.

One thing I did find the other day was there was some gunk in the mbc output pipe. Fitting the mbc in backwards (oops LOL) must have flushed it out, so maybe that was preventing the pressure from reaching the wategate actuator.

[p fandango]

if the MBC was blocked the actuator wouldn't open at all & you'd be getting more boost

[Dangerous Dave]

Yeah, so I'm thinking that before I rebuilt the turbo, the mbc was doing nothing

[AlanG]

Strange one as MBC's are very simple things. Have you tried removing it from the loop to see what,if any difference there is?