My '97 E300 OM606 has been knocking alot these past few weeks. When cold it sounds bad, like a bag or marbles. Even after it will come up to operating temperature it will knock when the idle is bright up slightly.

In addition I have started using Primrose last tank full. I choose the Primrose for it's lubricating and emulsification properties, to ensure my tank is free from water.

Last week I had replaced my fuel filter and it didn't have visible black particles, assuming I have no algae problem.

When accelerating at sporatic moments I may have a slight hesitation. Sometimes gradually accelerating from a traffic light, I will see some visible smoke behind me, something I never noticed before. Even right after my EGR mod.

And finally I have noticed my mileage drop. Last tank recorded yielded 19MPG and I ride on 18" monoblocks with moderate, non-aggressive driving techniques.

Tomorrow I will top off with fresh diesel and a few ounces of Primrose. I fill up at the same station almost every time, local Hess.

If this does sound like possible injector related issues, what would be a reasonable repair? Replacement of injectors? How striaght forward is replacement of the injectors. I heard that the injectors even if new, must be flow tested. Should I buy the injectors from the local MB stealership and have them test the flow pattern on the spot? My E has about 142,700 miles and thrid owner with no records of such mechanical work. So from my limited knowldge of diesels I am hoping that it is only an injector(s) issue.

Thanx in Advance,
Chris

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#dieselFLEET
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'97 E300
'99 E300

What you describe is called 'nailing' because it sounds like hitting a nail with a hammer--and is what the fuel ignition is doing to the piston and rod bearings!

A proper injection/ignition process goes like this: When the piston is coming up and reaches the point when fuel injection starts (the injection pump has to be 'timed' to start the injection at the right point in the compression stroke) and the injection stroke starts, the fuel is sprayed into the prechamber and starts burning with only a very slight delay (ignition delay), and the flame contimnues throughout the injection stroke, creating the high temperatures and pressure that drives the engine.

It is caused when fuel is not properly atomized during the injection pulse--and it takes too long to start burning. When it does, there is so much fuel already in the cylinder that it goes 'bang' rather than a continuous burn throughout the injection pulse.

Partially clogged injector nozzles are the most common cause. Faulty injector pump discharge valves will also cause this as they 'leak down' between each injection stroke causelow injection pressure.

First place to start is remove all the injectors and have them cleaned and tested by a shop qualified to do it. (truck repair shops do this all the time.) Maybe your MB dealer has the equipment most do not and just sell exchange injectors. 90+% of the time the nozzles can be cleaned. The fuel passages in the nozzle are extremely small and precise, and even one of the 3-5 holes plugged will seriously disturb the fuel spray pattern. I have seen some that shoot out a solid stream rather than the 'fog' pattern necessary

Injectors can be cleaned / tested for pattern, most are repaced with reputable "rebuilt" these days, and are a safe bet, I think even the BM dealers offer recon injectors by Bosh. At 140k it is a safe bet, have them check the compression at the same time, change the "bypass hoses" check "cigar"!

You might look into servicing the delivery valves if the 606 injection pump is anything like the 603 injection pump.

Sixto
95 S420
87 300SDL