I'm putting this under Electrickery but it's just a guess...
Recently, with the colder weather, the Duchess has decided to be a little bitch to start when cold. She used to start absolutely immediately, hot or cold, but now she can take repeated attempts to start. The starter/battery seem perfectly healthy and the engine cranks over nice and quickly. Eventually she'll start on a few cylinders and then the rest cut in over 2-3 seconds.
Where should I start looking?
Is yours diesel? Glow plugs could be on their way out.
Has it had a new set of spark plugs recently? If not it might be time to try starting with those as the simplest thing first.
Its not a diesel, says its the 4.6 in his signature.
Ah, sorry. I'm currently on mobile and not seeing any signatures.
If it's worse in the cold and damp, I'd say you are looking at HT leads breaking down. Polishing the coils helps too.
Is the nano not showing anything ?
The last fault I saw on the Nano was to do with a low voltage on a serial bus (or similar). I'm afraid I just wiped and carried on because I was late for work. Now I know it'll start eventually I'll take down the details if it comes back but I didn't think it was related at the time.
Bad technique, I know :(
If it's cranking fast enough it wouldn't seem that the battery or charging is the problem but low voltage diagnostic codes don't agree with that.. It's possible to get used to slow cranking (if it slows gradually enough over time) and think it's cranking OK until you put a new battery on and see the difference. Could be down on compression and have a duff battery / alternator (lol - not!).
Agreed with other people, ignition seems likely.
Also is there the chance of some module / immobiliser getting low voltage..
Dodgy crank sensor
Dodgy petrol pump can cause missing on some cylinders when starting if slow to keep up with pressure when ignition is first turned on, as can dodgy pressure regulator.
I checked the Nano - P0134 Lamda Sensor Upstream Catalyst BAnk1 Drive Cycle C. Occurred 1 time. Signal Invalid. Fault is not currently present.
I cleared it, but if it happens once in a couple of weeks...
I also did a quick clip of it starting, of course it was fine because it had been started already today. It seem to have to be really cold/a long time since the last start before it makes a difference.
One car that I became very familiar with a few years ago had a little quirk where it either didn't, or was very reluctant, to start if it was cold and damp. This had an old school distributor and coil but the principle will be the same. Due to where the coil was mounted, over time it got a layer of oily dust on it. As soon as it got damp instead of the sparks travelling down the HT leads they would track down the side on the coil terminal to ground resulting in no spark at the plug. The cure was to simply polish the dust off the top of the coil. I knew someone who was convinced his car had a moral conscience as it would start perfectly no matter what the weather if he was at home but if he stayed overnight at his girlfriend's house it would refuse to start the next day. Difference was that he put it in a garage at home but it was left outside at his girlfriend's. When I told him that he needed to polish his ignition coil he thought I was taking the piss but once I'd explained why he did it and was able to stay out anywhere he liked overnight after that.
Now I know the coil on a Thor isn't the easiest of things to get at but I also know how much you like polishing things so give it a try.
It was -1 degrees this morning and she started like a champ.
I'm not sure if I'm pleased or not! :)
But was it a dry -1 or damp? I suspect at that temperature it would be dry which would support my suggestion.
There was ice on the windows, but what the humidity was like in the engine bay... dunno!
It might be worth having a look under the bonnet when its a problem if its dark, if the sparks are tracking away from their correct location you might actually be able to see them.