just cause glow plugs are getting voltage at bus bar doesnot verify, just as has been pointed out at solenoid or like, partial current may be flowing. also by hooking up a voltmeter its completing a partially 'false' circuit, it will tell you the first of the steps for glow plugs troubleshooting, voltage is there, not if its being used, in -0- glowplugs, or say 1 or 2. have to keep on going to make sure glowplugs are actually getting hot enough, each, usually.
i dont see why you cannt have low compression that will make hard starting with out much, or little cold smoke, check compression anyways. is a symptom of his/your problem. a little puff of cold smoke can easily and possibly normally be cold fuel smoke, but check. just do one thing right, realize how injectors come out and go back in, find the info on how to hold breaker bar to, so you dont crack inj (weak)(&supposed) bosses. and lose head. oh and when putting back in it would be best to there use a torque wrench.51 i think.