As already stated. Diesel knock is caused by a poor iinjector spray due to a worn or partially blocked nozzle. A leak back test will not show this or enable you to cure it. A diesel specialist will be able to test your injectors and overhaul them.

Don't you long for the old days of indirect injected Diesels and mechanical pumps, which given a bit of looking after lasted indefinately and were the most reliable engines ever made.

Suspect injector? remove injectors which would take about 20 mins cos basically they were in the same sensible place as spark plugs would be on a petrol (so any injector seal leak didn't mean carbonised oil leading to eventual engine destruction), nip 'em over to the local Diesel shop who'd clean and test them and if necessary rebuild them.

Last set of injectors i had to remove was on my Renault 21, easy to work on, cleaning and testing the set cost me the princely sum of £40, so about £120 today.

Not as easy as that,

Basically they all should leak back the same amount,

No more or less,

Either means a possible fault.

A scan with Renaults can clip will give an injector correction figure,

that will point to an injection correction factor that "could" account for the smoke.

And remember Renault number their cylinders from the gearbox end so THAT'S # 1 cylinder.

So be very careful if you get a fault code for say cylinder #2 that you go to the right cylinder injector.

in this case that would be the 2nd cylinder in from the gearbox.

"Can Clip" is Renaults own diagnostic program.

You can get them on Ebay but try you local diesel specialist for a scan.

Will cost less.

Or even the EGR valve sticking

Anyone any ideas

As railroad stated diesel knock is simply either incorrect timing or much more common is too much fuel from a failed injector.

Or if you wish to replicate "knock" just listen as some b***** sprays starter fluid into an intake.

Chills my blood!

You only use the smallest amount of fluid.

Anyway the real reason for all this technology on vehicles is very simple.

Correct diagnosis.

A scanner of the correct type plugged in and the correct knowledge/experience will give indications of where/what the fault may be.

So you scan it and read on the live data the injector fueling correction values.

Or the more expensive way is remove all injectors and send them of for testing.

Scanning it make financial sense,

it may be theres only one outstanding correction value so THAT is the only injector removed and tested/replaced.

SCAN IT!

Blimey - quite a noise.

The smoke out the back is definately unburnt fuel no codes or lights on dash

Cant see it be a piston hitting a valve as the engine would of chewed its self up by now