just got in from work and had a right palarva on the M1 on the way back sittting at about 3000 rpm and couldnt help give the 'switch' a flick to tweek the boost to 18psi. Boosted it and when she came onto boost it pop and banged like a mofo now my boost gauge only reads up to 1 bar then goes off. i noticed it go right round till it physically couldnt go any further when it came onto boost. Now im pretty sure the banging was lack of fuel due it spiking really hi but i cant understand why it suddenly boosted so hi. When the switch was off (set to 6psi) my gauge was reading about 10psi. whats going on???

any help would be mint thanks peeps