Exhaust blowing

[montana]

A couple of months ago i had the exhaust off from the downpipe and replaced the manifold to cat kit and sealed the other joins on the centre section and backbox - I have rechecked these and they are not the source of the blow.

I am thinking it could be coming from the manifold to engine area, need an assistant to help me check this though.

Anything else to check ? It sounds like an obvious blow but could it be anything else ? Injectors?

Thanks