Re: alfa GTV V6 2000 Turbo
I have had similar problems in the past. On two occasions, disconnected pipes have been the cause, the large ducting from the intercooler had not been refitted correctly in the past and split at the jubilee clip allowing boost to leak. Secondly, when repaired the pipe popped off at the other end, I guess it hadn't seen that pressure for some time. Both produced a case where the engine functioned fine until the boost came on, then the engine misfired and wouldnt rev further, I guess overfuelling? In the other case, I found the distributor cap and arm were knackered, this again, oddly, only really showed itself as boost was coming on line, at this point it would not rev and would even pop and backfire.
I would have thought that if the wastegate were stuck open you would hear the gases escaping, my wastegate is quite audible even when dumping gases at 3500rpm. I am by no means an expert though.