Quote
How did you measure the resistance of all 4 plugs?
Try to clean the plate that connects all the plugs, maybe you have a bad contacts here.
But anyway, at +15 engine should start easy, even you have no plugs at all. I would check the injectors. If injector doesn't spray properly (leaks), the cold engine can't burn the fuel. When temperature rises the engine is able to burn anything the injectors supply. It seems similar to your condition.

I took out each plug, and measured resistance with a digital multimeter. I made sure the contacts were good by etching the points onto the plug. I also cleaned the bus bar plate, wire brushed all contacts including the wires.
I'm planning on swapping glow plugs off a good starting Pajero onto mine and see if that improves anything.
BTW, have any of you heard of modifying the 4d56 glow plug module to a modern delco or bosch system?