+1C yes, -1C no, different injection maps and injection advance for different temperatures.
It's possible last year you've had 2-3 good plugs, now maybe you have 1 or none functional.

Also the glow plugs doesn't purposefully heat neither the injectors, nor the air.
Yes, as a consequence they do, but their heating is too small and concentrated in order to have a big chance considering the big chunk of metal around.
Their main purpose is for the fine sprayed fuel to encounter the incandescent tip and catch fire much easily.
This is why they are ON for a long period, even after the engine is started, in order to help to have a clean combustion.
So, an inconsistent spray pattern on the injectors, that is avoiding glow plug incandescent tip, will not help either, even if you have good plugs.

Alex , that’s a very good comment/ point, you really know your stuff !

Try replacing the crank and cam sensors. Mine would start then stop numerous times with no-starts as well. Was worse at low temps then started to creep in at all temps. Replaced both, neither was a hard job, about £20-£25 each and it starts first time now. I have also replaced glow-plugs on mine, the Ford engined 2.2 TD4, but it was a long job removing the intake manifold, egr pipes, etc. Give these a go, try the crank one first as it is a 10 minute job.

Could anyone supply a diagram or picture of the location of glow plugs relay?

What year is it? If its a pre-2011, the there's no glow plug controller, as they're powered directly from the ECM, unusual but it's seems to be correct, at least as far as I could tell. Hyundai Ioniq 5 Ultimate. The family car.
2009 Rimini Red SE TD4. Gone.
2006 Tonga Green i6 HSE. Gone.
Audi A5 convertible, my daily driver.
1972 Hillman Avenger GT, the project.

Pre My2011 models use 11v glow plugs & relay, located in the under bonnet fuse box. Post my11 models use 5v glow plugs & a control module located next to the engine ecu under the plastic panel forward of the windscreen.

edited to keep Grimdog happy  (Now Sold). 2008 Freelander 2 (Nazca Sand) SE TD4 Auto. Statutory write off & on WOVR for hail damage but still road legal.
171037Km as of 09/05/22
Superchips Bluefin Flash
Nanocom Evo II (also sold)

Last edited by Badger51 on 26th Sep 2021 10:26 pm. Edited 1 time in total

@Badger51, I think pre MY11 they are 11v not 12v, just did mine this last week.

@Grimdog of course you are correct but the only concern is in using the correct one of the two, as many people have found out to their cost . (Now Sold). 2008 Freelander 2 (Nazca Sand) SE TD4 Auto. Statutory write off & on WOVR for hail damage but still road legal.
171037Km as of 09/05/22
Superchips Bluefin Flash
Nanocom Evo II (also sold)

Nodge68 wrote:

What year is it? If its a pre-2011, the there's no glow plug controller, as they're powered directly from the ECM, unusual but it's seems to be correct, at least as far as I could tell.

@Badger51, yes I nearly bought the wrong ones, but one of our sponsors AF put me on to the right ones for my MY 2010.

https://www.advancedfactors.co.uk/lr001302...-774-p.asp

Good job as three were open circuit, one reading high.