Sudden intermittent non starting

my wifes TD4 has suddenly started playing up, once earlier today it wouldnt start, then eventually it did, then again later when trying to go to fetch the kids, she gave up and used my van. when i came home it started? but then immediately wouldnt start when i tried again?

i stuck 10l of diesel in as it was approaching the red mark, and still nothing.
under the bonnet i found nothing visually wrong, except a small rubber tube, with an inline filter on the end,flapping about at the rear of the engine, had a look around and the only 'end' i could find that it would fit on was a steel pipe that came up the rear of the engine on the drivers side and near the top it bends over and points back down and was open ended, so i reattached the rubber tube, but again it wouldnt start?

after about 5 or 6 attempts it started.

i have absolutely no idea what s going on.

any suggestions will be appreciated, im guessing it maybe electrical? if so, what/where to look

first things first, unattach the rubber hose which you have attached, they are both vents and designed to vent to air. the one with a filter is the turbo vent, and the other is the vent for the IRD. Both must be open to air. (tis a common mistake)

possible causes could be a crank/cam position sensor, usually worse when hot,

OR (and it sounds a bit like this)

a faulty injector, search this forum for leak back test to see how it's done. Basically, the ecu requires the pressure at each injector to be equal before it allows the engine to fire. If you have a faulty injector, it allows diesel to leak back away from the injector, which creates a pressure imbalance. A leak back test measure the leak back flow from each injector, and you can see at a glance which one(s) are causing the problem as there will be vastly more diesel in the bottle.

good luck.