ScottMellor

Overboost will not occur in lower gears because there is not enough time or load to build much boost.
My old car, Frank, would do this sometimes if I floored it at low rpm in a high gear. When the revs passed 4500 there would be a significant shudder. I just learned not to do that.
If I was rowing through the gears at maximum throttle, it did not happen.

Basal Skull

+1 not really a shudder but slight loss/decrease in acceleration. I believe Kevin said that that's the way these motronic engines are tuned, you get peak cylinder pressures through 4500 rpm or so, and to 'protect' the engine, boost is pulled over that rpm range, then picks up again after 5000+. I'll go see later if I can find an example in some data logs.

Felix

It's worth connecting a boost gauge, if only temporarily, to see if the computer is reacting to too much airflow which allows too much boost. The N75 valve can get lazy over time meaning that when the airflow starts to near the maximum allowed for that set of conditions (rpm, load, IAT, etc) and the computer starts to ask the N75 to bleed boost via the wastegates the slow reaction of the N75 valve means too much airflow actually occurs and the computer reacts to protect the engine.

mausone46

today everthing works fine, boost as much as desire!!!
Last time maybe heavy trafic with low speed was not healty for this engine

luizinholeao

Scott, BasalSkull, Felix, Mausone:

Thanks for the help... do you think the N75 valve could get in trouble by excess of oil? when i bought this car it has lots of oil in inlet and exaust systems...
Luiz