Outer Limits 4x4 Board

Ok my mates 2.8 turbo diesel (yes Guts it's a white Hilux ) has developed a pronounced knock mostly at idle and a trailing throttle (motor has done 400K's).
He thought he'd done a rod bearing and replaced them today (x4) but it made no difference.
When fuel is stopped to no-2 the knock stops immediately so he's isolated the noise to there.
Could this be a crook injector ?? His injectors were all replaced 25K ago with brand new items.
Any idea's ??
My suggestion was to pull out the 2.8 and put in a Mitsi 3.5 V6 but he threatened to stick those rod bearings up my clacker

have you checked your rocker arm to valve gaps they may need adjasting mine (3b) had a load ticking when at idle adjasted all and now its as good as new. i also have nosiey throw out bearing which stops when you put the clutch in and is a very loud knocking noise at idle. chris

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Sounds like injector. Try swapping it to another cylinder and see if the noise follows.