Oh yes indeed about the glowplugs staying on for a while after firing! There have been some interesting designs where the glowplugs stay on all the time the engine is running.
Of course, it will be microprocessor control that determines how long your glowplugs remain active.
Some glowplugs go "bad", meaning the resistance rises somewhat during service. These are easy to miss during the check with an ohm-meter, this is why I specify a test with a heavy current test lamp between battery +ve and the disconnected plug-tip. If one plug gives a dim light, it's gone high-ish resistance.

Leedsman.

 

What seals are used in replacement of filters to pipework. I remember an instance where I couldn't get the pressure up on a newly fitted pump filter. I had used the old copper seals which looked good after an emery reface. I ended up have to buy new seals which come annealed for the squash leak proof seal.

 

ok have checked all fuel filter assy ,all seems tight have sprayed all round the filter head with soap solution ,no sign of leaks.
I went to it this morning (been stood since Friday afternoon ) and the primer bulb took 5 pumps then went rock hard and the engine fired straight away,that leads me down the air leak into fuel lines path ,but am puzzeled where from?

 

Note that spraying around the filter head will not show up where air is being sucked in.

 

Low pressure end first, check the (1) spin-on filter is not loose or the (2) white plaggy water drain tap on the end of the filter [assuming its an 04 to 07].