Changing all eight injectors question

If you want check your injectors you can measure the armature plate clearance with a feeler gauge while still in engine. This will tell you if the wear is down to under accepted spec. Simple to check once the valve covers are off. Post back if you want more details.

You may just have glow plug issues also.

to check aramature plate clearance you need to pull off 4 screws on top of injector and pull off the solenoid. Then pull off spacer. Now you see a square plate which is the armature plate. A feeler gauge is used to slide under neath the plate. A new injector spec is .004 in
A minimum of .0015 in is needed. If you have a .002 in feeler guage and it will not slide in that injector is just worn out.
I had 5 bad ones that would not pass the spec and I replaced all 8 injectors. My cold start problem was then gone. This was only done after doing all harness and glow plugs and relay.