I had the exact same problem with my '91 350SD. Start the car ice cold, for the first two minutes so silent and smooth running almost like a gasoline engine. Then a slow steady progressive drop into non-stop continuos nailing. Nicest sounding engine turns into the worst sounding engine ever diesl or gasoline. Drive the car and it's gone, return to idle, back with a vengence, ping! ping! ping!. Removed the old injectors, put in new ones, no improvement whatsoever, take them all out have them pop tested, all checked out fine, reinstall, same nailing. Suggestion to try diesel purge, wow impressive stuff, so long as diesel purge is running through the system, silent running no nailing whatsoever. Beautiful silent even idle. Connect back to regular diesel fuel, non stop nailing. Non stop only at idle, when the RPM's were increased or by driving the car all nailing would leave. Spent hours reading every nailing post, same suggestions repeated over and over again, pop testing, injectors, diesel purge. Then searched all Mercedes forums, found a one line solution, add one quart Canola, Corn or Peanut oil to one tank of regular diesel fuel. Add prior to filling up with fuel to allow mixing. After a 20 minute trip, all nailing gone, not sometimes or occasionally gone, gone forever. Fixed! It apparently causes no problem with fuel gelling because it such a small amount. I'm in upstate New York, routinely goes below zero, has never caused a problem with cold weather starting. I don't know if it will work for you, but it cured my problem.


'87 560SL 150,000
'94 SL500 40,000
'91 350SDL 514,000 (canola oil additive to stop nailing vehicle)

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jcciem
'94 SL5000 60,000
'91 350SDL 545,000
'91 350SD 197,000
'00 E55 AMG 77,000