Welcome to the forum. welcometomyturbodies
Well I'm not sure that you can test for a blocked exhaust on a diesel as you can on a petrol engine.
On a petrol engine you would use a vacuum gauge plugged into the inlet manifold to measure the manifold vacuum then you would increase the revs to about 2000-2500rpm and the vacuum should remain constant, if the vacuum drops then the exhaust is blocked/blocking/restricted.
With a diesel there is no direct manifold vacuum so this would be difficult to check. You could try it as you have nothing to loose.
Oxidising Catalytic Converter