Thanks for your response,i've removed sump pan and checked pressure relief valve all ok also checked oil pressure on another hdi and it's about the same also autodata tech dept tell me figures given are only minimum expected pressure.
No there is no inlet flap.And i removed front pipe first off as it felt like a restriction.
The strange thing is there were no fault codes etc,no excess smoke and customer said it happened all of a sudden, no doubt i'll get to the bottom of it but just wondered if anyone had same experience