Part of the reason I ask is that in my case a coolant leak into one cylinder caused the white smoke on startup, difficult starts, and although I am usually able to identify an odor thanks to a nose the size of a small country, in this case I couldn't pinpoint it. It did not have the usual very sweet smell of coolant being burned, and since I was running B100 at the time, I attributed the issue to fuel. ("Doesn't smell sickly sweet, or acrid like engine oil, so...")
I don't know what had me fooled: maybe the HOAT coolant smells a little different when burned than what I was used to. But I was fooled. And eventually the coolant leak got bad enough to nearly hydrolock that cylinder. I was lucky not to have caused more damage than occurred.
I'll add that even in single-digit temps with biodiesel blended with petro, I've never had big clouds of white exhaust on startup that lasted for a bit. I've had puffs of grey that immediately seemed to not be added to after the engine was running even at idle. Nothing more. Not to say that one of your injectors couldn't be leaking.
My understanding of the fuel rail is that it isn't a good pressure reservoir: without an air pocket in the system, I would expect pressure to leak off very quickly. In fact, when I shut mine down with good working injectors, I can see something (Pressure solenoid at back of rail?) bleed off pressure very quickly, going from 6kpsi down to around 90psi in short order. So I wouldn't expect enough pressure to stay in the rail to cause even a faulty injector to leak much into a cylinder after it is shut down.
and worth every penny for that opinion, though. No data other than cited.
So at the risk of biasing the OP, I would double-check to make sure that fuel is the issue.
gmctd wrote:
crank it up, walk back near the cloud of white VAPOR, get a good whiff - strong odor of raw Diesel fuel is uncombusted fuel - if not, post what you think you smell.
Sounds like a great approach. Or get your wife to crank it while you kneel back there in the firing line. Mine was way too eager to help out that way...kept giggling and muttering something about "not standing in the way of voluntary asphyxiation."