[carbon]

If the compression on cylinder 4 is low that will cause the white smoke, when the cylinder warms the smoke will reduce - clear. A cylinder leak down test will help diagnose the fault as to wether the piston rings are broke or valves worn by the direction the leaking air takes. Had something similar with a Volvo truck white smoked at start up but cleared after a couple on miles enough to pass the mot checks but I wasn't happy with it. Performed a leak down test and found two cylinders were lower than the rest and air was escaping through the bottom of the engine rather than the cylinder head. Took the pistons out to find the second rings on both pistons were broke. Had caused no damage to the cylinder bores so was lucky

 

[carbon]

Faulty injectors can not affect the compression of a cylinder. Piston rings, pistons, cylinder head gasket and valves affect the compression of a cylinder

 

[carbon]

Ok should have included cracked cylinder head but op has already checked for that so didn't include it. Similar problem that the older LT engines suffered with cracking between valves. A leak down test should identify a crack in the cylinder head as water bubbles in the cooling system