Ideally you need to get the fault codes read but off the top on my head if its a diesel type knock I would say its an injector problem. Usually happens when neat unvapourised diesel is getting in.

You can have leaking injectors and the car running really quite well without generating fault codes, but get the injectors re-seated and then you find the car is running so much more smoothly. Is there any sign of fuel dribbling down the side of the engine? In my experience of running a diesel, the problems you report are more than likely to be caused by the injectors - either leaking or mucky. If there is no sign of them leaking, try changing the fuel filter and fill the new filter with a good injector cleaner before reconnecting the fuel pipes and starting the engine.

Don't try to get injectors done on the cheap! I was boasting in a discussion only a few months ago that I had found a local garage who would do my injectors for just £120. Well, he put a deep screwdriver cut in one of the injector seats by trying to beat out a stuck copper seat 'cos he didn't have the right tools. It's now cost me a further £360 at the diesel specialist, who warn my that the screwdriver cut is too deep to re-cut completely and that they've done the best they can, but it'll blow again.

Edited by MrEckerslikefromRamsbottom on 04/04/2014 at 22:18