Most diesel engines are hard to start when it is cold. Plugging the diesel engine block heater in will help the engine start.
It is not so much hard for a car to start when the engine is cold as it is easier for a car to start when the engine is warm.Cars that are hard to start in the cold are usually not new cars any more and because of wear and tear there is more likely to be something that doesnt work as well. when fuel is warm it ignites more easily.
Needs a tune up?
The engine won't start or will be hard to start in cold weather unless you have the motor heater plugged in.
Try replacing the engine coolant temp sensor.
thw weather is cold?
If there is no check engine light illuminated, start with the basics like a good tune up.
its too cold
It does not have a cold start relay. It sounds more like a fuel pressure regulator has failed or the injectors are dirty causing excessive flow. Have a certified technician check for these things as they can be a little hard to diagnose without the proper equipment.
have vehicle scanned to determine the problem
ck coolant temp sensor
Try an engine heater or an oil heater. These are both inexpensive.