just to be sure, pull vacuum on the out port of the pump to suck some fuel through.. suck a good amount to confirm no bubbles are coming. then try to start.
you can have REALLY bad compression and still be able to start at 0C with good glow plugs. you do need good injectors though... a bad injector or two will definitely make it near impossible to start.
when you start it at low temp, does the motor catch, or sound like it wants to start? or does it just sound like a gas motor without spark?
One thing I haven't seen anybody mention was the cold start device. I guess your car has one doesn't it and is it working? My car starts a lot slower even in the Summer over here if I forget to use it when the engine isn't warm. Maby your cable pulled loose and it's not working, just a thought. More than likely it is compression though
A little check list to help clarify perhaps?
Glow plugs get power when the key turns *check*
Are there air bubbles going to the injection pump on first starts in the morning?
Maybe try adding a block heater?
All else fails you could take the injectors apart (follow a guide posted here on the forum) and see if your nozzles are jammed stuck. You may need to replace the nozzles. They do wear out and as jtanguay mentioned they would make cold starting really down right STUPID and frustrating to deal with because it is relatively difficult to tell if you have bad nozzles... without it being brought to your attention first.
Does the motor while running have a bad knock? - put a screw driver to each injector while it's running, put the butt of the driver in your ear and listen to each one. If you have really bad nozzles you will hear a very clear "knock" sound. Like a clack sound that really just doesn't sound right. Or and injector/injectors that sound distinctly different than the others.
I hope that helps a little bit!
(ps, this problem + burning oil makes me think rings are gone but let's not jump hastily to big jobs here!)
(pps, the answer to jtanguay's question about what it sounds like when it's trying to start would be a good clue too! he really knows his vee dubs.)
Hi again guys
My car has started to start now. The problem was the gp's. I took them all out again, two were not working. So replaced them and it cranked into life.
So thanks all for your help!!!