My Vauxhall Vectra is failing to start first time in the morning. It has to be turned for around 30-40 seconds before it will fire up. After that it will start first time at any time of day. The glow plugs have been changed, the fuel return pipes have been renewed, the pressure valve has been renewed and a full service carried out, but it still gives problems starting in the morning. I was told to clamp the return fuel pipe coming from the pressure valve feeding the excess fuel back to the fuel tank, and when I do this the engine starts first time. This is why we replaced the pressure valve, but unless I fit the clamp the night before the engine has problems starting. Can anyone help?