My JTD has been having starting issues on and off for the past couple of months and at first I thought it may be the glow plugs but thought I would wait a bit to see how things developed to get a bigger picture etc.

When the weather was sub zero (down to -13c) over the last few weeks it started first time every time believe it or not but the engine turned slowly obviously due to the battery not having as much power. But now the temperature is warmer and the battery has more power the engine turns over much faster but most of the time it won't start first time but almost always second time even when hot. My question is, how can faster cranking be associated to the engine not starting first time? Any ideas??

Just to add. When the car runs it runs perfectly with no issues at all.