I don't know the exact figures for the AAZ turbo, as mine has a JX one, but most of these diesels and the JX too all run about 7.5 psi boost, thats about 0.5 bar boost. Small differences I wouldn't worry about because a lot of the time the waste-gate or Blow-Off-Valve limit it.
Don't forget the wastegate doesn't just suddenly pop open at a given pressure, but starts opening gradually so that turbo rpm are dropping off quickly enough to avoid overboosting.
The AAZ has a closer coupled and a slightly larger turbine compressor, which is not just about boost pressure, but about the onset rpm and efficiency at its design point (boost pressure and flow rate).
One thing that might be happening is the wastegate is not sealing that well, and you're losing exhaust energy prematurely. BOV might be popping prematurely too (or just be set low on this engine) - I blocked mine up completely (a cork
)
Wiki on turbos shows re-cutting the wastegate poppet valve..
Check and replace the air-filter, they don't like pulling against a vacuum..
How do you test yours, how do you know if its working pretty well to spec.?
Easiest way - put a bleed valve in the wastegate line - then open it up in stages to see the boost increasing. With the BOV blocked, I'm getting about 12.5 psi with it almost fully open. This seems limited by the small JX turbo compressor. If boost doesn't increase much or at all over .5 bar think there's something wrong.
Difficult way - look into the compressor inlet and inspect compressor wheel for damage; rock it around to check play on shaft (0.020-0.030" acceptable, slight rock, acceptable). Remove and check wastegate valve condition and general turbo condition..
Alternate - disconnect wastegate pressure feed line and (gently does it) see if boost increases before BOV pops.
NB. Don't jump to conclusions without evidence from two tests confirming the situation.
Also think not all AAZs the same, certainly injector pump-wise. Just go with what you've got and get the boost nearer 10~12 psi if you can. Then start winding the fuel screw in a bit (1/4 turn to start with)
