2006 X5 Diesel intermittent cold start problem

[powers1]

Originally Posted by opienor

Thanks powers1!

The problem gradually intensifies as outside temperatures drop. Lower temps equal more start attempts. Worst case happended at -4 deg. Fahrenheit when the engine just wouldn´t start at all and the car had to be towed. I´d say the problem appears between approx. -4 to 23 degrees F.
I think you may be right about this being some sort of a sensor or electronics related problem. Especially since I can clearly hear that the fuel pump fails to activate the times the car doesn´t start. Something appears to be wrong in the startup sequence. I glow, fail to hear the pump, crank with no start. This is repeated a number of times until the pump (I assume) suddenly comes to life when ignition is activated, the glow light goes out and voila the engine starts. I have tried to go from off to ignition without cranking a number of times to see if the pump suddenly starts, but without any luck. The cranking (without start) somehow seems to "wake up" the pump for the next start attempt.
The glow indicator lights up and then goes out before I start cranking. Everything appears normal in that department. And no error codes I´m afraid.

Well,its when you dont get the error codes ,and the engine doesnt start,that the hard work starts
Have you tried waiting 25 secs before cranking the engine?This is about the time the glow plugs take to turn off and will give you more heat to burn the diesel and start the car.
The coolant sensor is also influencial in the start procedure,so get them to have a look at that.
Another thing is if your EGR valve is closed ,it wont allow air into your engine and it will starve and wont start.To test it,You can pull off the vacuum pipe to it and see if it makes a difference.
The best way and we do here is we do it by trial and error,by replacing the sensors I mentioned above.
Today ,we had a 330d E60 that wouldnt go above 2500 rpm when the engine coolant temp (ECT) was between 10-50 degrees...!After this temp, it was fine!No error codes !We replaced the obvious sensors...nothing!Tried the turbo solenoid and voilá...all good...
I leave you here a pic of all the sensors in the engine compartment.