OM603 CHASING DOWN THE STARTUP SMOKE

'87 300SDL OM603

Near Los Angeles, temps always between 55 and 85


The mighty 300SDL had been smoking and clattering on startup until warm. I replaced the glow plugs and reamed out the threads for carbon. Also removed & cleaned injectors (which weren't very dirty, I think they have less than 50K on them), but didn't pop test and rebalance. Was quite careful to not mix parts. Car ran without much smoke after this for a few thousand miles, even on kick-down acceleration. but still clattered on startup and somewhat on idle, and still has one cylinder nailing when cold.

Because of an oil leak, I just replaced the front crank seal and the vac. pump gasket. Oil leak is gone, but now the blue-white smoke on startup is back. It smokes very badly, enough to attract attention and complaints, gradually subsides until the engine is fully hot. The smoke smells only of diesel and seems to be unburned fuel. Smoke on kick-down acceleration is now pretty bad again.

The glow plugs all test at about 1-2 ohms at the glow plug relay. The relay tests good for all six glow plug circuits(delivers 12v to all).

Compression COLD front to back is 350, 380. 360, 320, 350, 350. Compression HOT front to back is 390, 410, and then my piece of junk Harbor Freight diesel compression tester crapped out on its EIGHTH cylinder test. But you get the idea.

Haven't been able to establish if there's excess oil use yet.

The Crankcase ventilator tube from the valve cover to the air intake broke from age when I pulled it off. Does anyone know what effect that hose being missing can have?

With the above glow plug information, can I get away with not taking the damn things out and trying them on the bench? It seems that I need to check the IP timing and pop test, rebalance and/or replace the injector nozzles next. Any suggestions of things to look at before I do those things?

PS, this is far and away the best repair blog/group that I've seen for Mercedes.

thanks everyone.
Bruce S