84 300TD 275K miles rough idling hard to start white smoke. Used diesel purge x2 with no improvement. I was assuming it is a injector problem. Any thoughts?

How long since the last valve adjustment ? .

It never hurts to remove and pop test the injectors but you should begin with the basics, every time .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Hard to start and white smoke with rough running immediately suggests glow plugs.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

X2 on glow plugs.

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

White smoke can also be from incomplete combustion from a cold cylinder or weak compression. Dead glow plugs or poor compression (bad valve adjustment, etc) will definitely cause it, particularly when the engine is cold.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Hold a piece of cardboard within smoke plume and then smell the cardboard. You will see if it smells like fuel or coolant.

The Glow Plugs are the easiest to check. It also could be the Valves needing adjustment.

Note that white smoke that smells like fuel is that what is making it white is actually the light on the atomized unburned fuel. I got a lesson on that when I timed my Volvo Diesel Fuel Injection Pump to early. It produced a large volume of billowing of pure white smoke once the engine was running.

Retiming the pump correctly and with some advancing was the cure.

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84 300D, 82 Volvo 244Gl Diesel

While it could be many causes, the two things that pretty much cured my wagon of the same thing (as well as being almost impossible to start below freezing) was running Marvel Mystery Oil in the oil through a couple of oil changes and after that using most of a 6-cylinder bottle of Engine Restore (dumped the remaining cylinder's worth in a different car just for kicks).

The MMO did the most, making it start well in the cold and getting rid of the reduced power until it warmed up. I suspect sticky rings is the main thing that it will cure. The Engine Restore got rid of the cold nailing it had since I got the car almost 9 years ago. I forget what all this one does but there's a thread about it on here with lots of similar results.

I'll also say that Diesel Purge didn't do a thing for me either. It made it run really quiet until regular diesel got back through the system but that was it.

Replace/ream the glow plugs and glow plug relay would be first things I look into if it came into my shop and the only complaint was rough starting when cold.

Another factor depends on your climate (not sure of your location). Are you starting in sub-freezing temperatures? Fuel could be gelling up. Make sure you have proper oil rating for extreme winter temperatures too. May need an anti-gel additive in the fuel for cold climates.

First thing I would do is make sure (a) you have enough fuel in the tank (b) your glow plug relay strip fuse is still good (costs $1 to replace). Keep a few extra on hand just in case because autozone won't have them.

Worst case could be bad/uneven compression (which valve adjust could fix unless burnt out valves/worn rings in which case you're out of luck), but since you say problem is on cold start, I would check glow plugs and relays first (easy and cheap), then go from there.

I agree on the gp check, use Bosch . Since you’ll be on that side of the motor it would be a good time to check its health with a compression check , just to see how the old motor is holding up.These engines will live a long life with diligence of their owners , your in good company.