If the BlowOffValve isn't working right what issues might it be responsible for? How will the car feel like when driving or accelerating? Is it traceable on a code reader? Is it common to have issues BlowOffValve?
The R56 doesnt have a Blow-off valve. It has a diverter valve with a noise maker that sounds like a blow-off valve down stream. From what I have seen unless you are running an aggressive tune the Diverter Valve is pretty reliable. If you had one that failed it would most likely leak boost pressure that would resort in lost power. Assuming it isn't a small leak then it would throw an OBDII code and CEL. What makes you think you have an issue?
Well i dont have over boost and in the whole range but mostly over 4000rpm there is power loss, but the funny things is that this doesn't happen always. Sometimes the car is fine, other times the issue appears! Does this make sense? p.s. what do you mean by running an aggressive tune?
It is possible to have a small hole in the diverter valve diaphragm with only minor symptoms like laggy boost initiation and slightly reduced peak boost, and no fault code, but it won't be that way for long once a tear starts. Limp mode and a dash light are the usual indicators. Remove the diverter valve and its diaphragm to look for tears. It's not quite common, but not rare either for the JCW version, more so when modified. Raised boost & torque limiter is one aspect of an aggressive tune, which can be a contributing factor in diaphragm tears.
The only faults I've seen with the OEM diverter valve, other than photos of broken plastic bits, are torn diaphragms. Reading forums from other cars that use or had used the same valve, I see no mention of problems with the solenoid, so it's most likely if you don't see something broken, it's not.
Not that im an expert but isn't it strange that the lack of power symptoms come and go? For eg. there are times that there is NO overboost and slightly less power in the whole rpm range and then there are times that nothing strange is going on, all seem normal. If there was something torn or broken, wouldn't that lack of power be a permanent issue?
Yes, that is likely, but there are exceptions. The hole in the diverter valve diaphragm on the right below was smaller before removing; I had to look very close to see it. The car it came from didn't have a problem till about the 15th minute on a race track. I can also entertain a transient leak or restriction for the vacuum tube serving the waste-gate, and a few other possibilities. In the photo below, a new model vacuum line is seen above, and the old below. Note the line/tube sheath on the bottom shows signs of heat damage. If the vacuum tube on your car does not have the rubber shield on it, replace it with the updated version as a troubleshooting step. In all the above failures a fault code was initiated eventually, which is what I would expect from malfunctioning solenoid also.
I worked on an R56 today that had a fault code after service at a dealership. Clamps on the inlet tube before the throttle body had not been tightened. If you don't think you're producing enough boost, could be something simple like a loose clamp.
but wouldn't a loose clamp be causing permanent boost issues? in my case some times all works fine, other times it doesnt