Fuel quality definitely makes a difference. Additives that provide Cetane boost may also help.
The glowplugs "afterglow" for about 10 seconds or so after the GP light goes out. No need to cycle them right after the GP light goes out. Just wait about 10-15 seconds after the light goes out before starting.
When temps are around 5*F or below, I do the following:
1. I get in the car but sit with the driver's door open so that the interior lights are still ON.
2. As I turn the key to "ON", I watch the lights above the mirror dim slightly. I know the glowplugs are really ON because of the drain on the battery.
3. After the GP light goes out, I continue watching the interior lights above my head until the GPs turn OFF about 10-15 seconds later. I can see the interior lights brighten up slightly when the GPs turn OFF.
4. Depending on how cold it is, I may repeat the process once.
5. Immediately after the GPs turn OFF, I turn the key to "Start" and it cranks and starts right up. It runs a little rough for about 10 seconds or so, but it always starts easily on the first try.
I've noticed in the bitter cold that if I crank it right after the GP light goes out, the engine cranks slower than if I wait until the GPs actually turn OFF. The extra load of the GPs on the battery while cranking the engine slows the cranking and makes for a harder and rougher start. The GPs also haven't had as much time to get fully hot, so they're not going to be as effective. It's easier on the battery and starter to wait a bit longer.
My battery is healthy and I'm not having any hard starting problems at all. My injection timing is right where it's supposed to be too. This is just a behavior that I've noticed in the bitter cold temps. I've found that waiting until the GPs finally turn OFF guarantees that the GPs are fully *HOT* and lightens the load on the battery during cranking. I've found in general that it starts almost as easily in the bitter cold as it does in the summer using this method, except for a slight roughness during the first 10 seconds or so of running.
Here's an idea for an easy mod I'm thinking about: I want to add an indicator light to the glowplug circuit so that I have a visual indication of when the GPs are actually ON. I won't need to watch the interior lights to dim slightly to tell when the GPs are ON. I want a REAL glowplug light instead of the light on the dash controlled by the ECU.
Just my $0.02 worth.
~ n1das