[Watsey]

I have found that the engine is running a lot smoother now, but it seems to be a combination of factors : clean IM and ports; Archoil AR6400-D Max engine / fuel system / DFP cleaner; and having the EGR coded closed (to all - spare me the lecture; I am not convinced that the theoretical benefits of EGR for NOX reduction outweigh the additional maintenance costs and fuel consumption).

Coding the EGR closed has made the biggest positive difference to engine smooth running. The annoying diesel tapping on light throttle between 1500-2000rpm has now all but gone, which supports my suspicion that this was related to poor combustion when the EGR was open.

Last week I did an intermediate oil change. Used LiquiMoly engine flush to (if you believe the bumf) clean all the internals, oil pathways, piston rings, etc. Yes, modern oils should have sufficient detergents to do this, but there's no harm in using a dedicated flush. Castrol GTX 5/30 LL04 and an OEM oil filter.

It's running better now (83,000 miles) than it ever has : smooth, pulls well, less harsh above 4,000rpm, and the lack of diesel tapping (probably 90% gone) has been long awaited.