Re: How is boost pressure controlled ?
The MAP sensor which is in the inlet mafold monitors boost pressure, it is a 0-5volt scale, but on idle will output 2volts.
The 8 & 10valves have a 2.5bar map sensor, that measures up to 1.5bar of boost at 5volts, no boost at 2volts.
The 20v and 16v have a 3bar bar map sensor, again 2-5volts but 5v at 2bar of boost.
The ECU uses this sensor and will correct the amount of boost using the overboost module, or VNT controller as some like to call it (thats the thing by the slam panel with the small vacuum hoses attached to it), this is a solonoid that opens and closes to control the amount of vacuum that pulls on the round cylinder type thing attatched to the turbo with a rod on it, the other end of the rod controls the opening and closing of the vaines around the turbo and directs gasses onto or away from the turbine wheel.