If you are hearing a 'pinging' from the engine, it is the injectors knocking. It means one is injecting excess fuel into the prechamber. Simple fix is to run a bottle of Red Line Diesel Catalyst in the next tank of fuel. Run the tank as low as you can, then pour in the Red Line BEFORE you pump the fresh fuel in. This ought to cure the problem, but I would still consider replacing the nozzles next year. It's quite an easy job. They can be had for about $45/each from Bekkers Import. Hope this helps!
'67 250SE Cabriolet
'93 300E 2.8