I would add the engine appears to be runing smoothly apart from noise. In fact I would add when the bonnet is down the noise is not that noticable. I have a feeling most people would not notice. It is only that the plastic cover that sits on the engine has a tendancy to vibrate that I noticed the problem. It accelerates fine.
I did use the srcewdriver trick today prior to writing. However I did not place it on or near the injector, which I will do tomorrow, but on the cam/rocker cover from which the noise appeared to be coming. I moved it about and it was loud just under the rocker/cam cover. I fear it is something to do with the rocker/tappet. However I am not familar with injectors. What I find strange is when cold it is not evident. Or as it warms up every other tappet settles down apart from one. I will have another look tomorrow.
@Coxey1.. How much effort and time does it take to get to the point you have with the cylinder head. To take a look would mean removing the cover. However I guess to change the rocker, if that is the problem, requires a bit more knowledge. I have rebuilt 4 cylinder 8v motorcycle engines from the crankcases up, including regrinding the valves, but we are talking along time ago and have never worked on diesal engines. Apart from changing a battary I have not got my hands dirty on a car for 10 years plus. Are the cam belts easy to re aline. If the cam had to be removed to change a rocker. I am probably getting ahead of myself here but I kind of know that the cover is going to come off.
I am going to ask. I need the car for Christmas as need to see the kids. I need to cover 200 miles before I will have a chance to look. A risk I know. Such is life. Wrecked engine or christmas with kids or rental car. What excuse will I have for my ex when I turn up in the rental.