Hmmmmm, boosting problem sounds odd, u sure the gauge is all ok (even though its a good make) they dont last forever, i know when u start doing wierd and wonderful things with the pipes they can have funny boost curves but it should be ok as is. Have you tried taking the amal valve out and running the actuator straight from the compressor housing?

Are collins in Bar rather than PSI or something then?

If the flap bobs up and down then i doubt there is an air leak, HOWEVER, my cabriolet was proving to be a bit of a never ending nightmare, ive had it on the drive for 7 months now, with all sorts of faults, like no fuel pressure, rough idling, and when left idling would slowly choke itself up until it stalled. Ive sorted it now.

One thing i did, which i would recommend to anyone running KE is to completely disconnect the engines breather system from the air box, should you get an air leak ANYWHERE on the engine, (ranging from a loose rocker cover, dipstick popping out etc) then the running suffers.

I think this is probably your route to go down to be fair, disconnect the breather and block the airbox entry (if only while fault finding), just to eliminate things.

No dump valve - thats 1 thing ruled out, notorious for problems.

Fuel pressure - you could do that, the way i check is to push the flap down after its been left over night, if its got pressure the flap will have a little resistance, and rise slowly and steadily, if not it will spring back up instantly.

Was it you i was posting about the fuel pump relay/wiring with aswell?

Its also worth checking you havent accidentally left any of the smaller connections off the battery terminals or anything, can cause ridiculous problems (guess how i know )