I have a 3liter turbo Hilux D4D...the engine seems to be noisy compared to other ones, there is also a one cylinder kind of light tap or knock, can anyone tell me if the tappets are manually adjustable or hydraulic. would an injector cause this noise? thanks, Mike.

You have hours of googling out there to do, first port of call the two UK Landcruiser forums (same engine in Landcruiser 120 series) and the Hilux forum, you'll find enough on those three forums to give you sleepless nights for a while.

Do not ignore this, complete engine destruction is a thankfully rare possibility (and only you know how loud this noise is), though it could simply be a noisy injector, those Denzo injectors weren't the best and one or two might simply be past their best and giving too much fuel, they are fairly easily replaced with recon units but its not cheap...is the problem loudest when cold and gradually disappears when warm?, if thats the case then it's probably just injectors need looking at.

More serious is if your vehicle was made before 2008, it's probably fitted with copper injector seals, these leak after a time allowing combustion gases to pass into the head, this contaminates the oil with carbon and eventually it can clog the pick up in the sump leading to engine seizure.

Many engines had seals replaced in service (my Hilux seals were done under goodwill in year 4 together with new injectors, ticking noise they call the death rattle), and even if they haven't beenchanged it's never too late, regular oil changes at sensible mileage helps even if a seal is leaking.

Whatever you do make sure someone drains the engine oil fully and either whips the sump off to check the pick up, or puts an endoscope into the sump drain hole and inspects with that, on the forums you will find pics of pick ups clogged so you know what you're looking for.

A thankfully more rare happening on these is that the pistons can crack, that was a new one on me but there a few videoes with sound on youtube showing what can happen.

If its only just out of Toyota warranty and has been well maintained then you might find Toyota will sort this under goodwill, always worth asking them first, they will know about the problems this engine has had, they upped the warranty to 7 years and around 110k miles for cars with sensible service histories.

The 3 litre is a great engine, but IMHO it was better in the early 90's when it was indirect injected and had a simple mechanical fuel pump, bomb proof then.

If its way out of goodwill scenario, and you don't feel up to tackling it yourself i'd put it into a competent Diesel workshops.