Glow Plugs

[AEROBAT]

My 1.9d HDI has been hard to start for some time. It cranks for some time then starts ok but lots white smoke, strong deisell smell. Runs fine when started. I decided to try and find out the reason. I checked all the glow plugs all OK. I then checked to see if there was any supply to them and I found that there was no supply when first turning the ignition on or cranking however there is a supply as soon as the engine is running and this stays live until there is some temperature after about 3 to 4 mins.
When I stop it and restart when warm there is no supply. This seems wrong as I would have thought the plugs should have a supply when ignition first turned on and maybe while cranking. Anyone throw any light on if this is wrong and if so where do I start to find the faulty item.
Thanks

[RichardW]

Bit confused...a 1.9d is not an HDi. Assuming this is a 1.9d then there will be a glow plug relay on the other end of the big wire to the plugs. This should energise the plugs at key on (along with the light on the dash) then the light goes out when enough heat. A short while later if you don't crank it the relay will drop out with an audible clunk. I think it's unlikely the plugs are not working - these are almost impossible to start without plugs working.

[AEROBAT]

It is indeed a 2.0 HDi. As I said it has been very hard to start. The plugs do not energise with key on and no dash llight. They do however energise as soon as the engine eventually starts. There must be some sort of controller that turns them off when the engine reaches a certain temperature. The engine bay is very crowded so until I know what and where to look. I checked the above by connecting a 12v lamp to the glow plug feed. This morning the overnight temp. was only 5 deg. C so I thought I would power the plugs directly for about 10 secs. by wiring directly to the battery and it startted first turn and no unburnt smoke. So I think that proves that whatever controlls the plugs is not working correctly

[RichardW]

OK, on a 2.0 HDi the plugs are only used pre-start in pretty cold conditions, switch on once the engine starts is normal to help cold start emissions. I think some other issue is underpinning the problem. Do you know if it is a Siemens injection system? These are fussy about the cranking speed, so a poor starter leading to slow cranking could be the cause. What car is it in / which version of the engine?