Internal engine noises can be very difficult to diagnose. A diesel engine can ping, cling, clang and bang, and all the time you are wondering just what is acceptable and what is not. Some knocking noises are normal and should be of no concern at all, while other deep noises can be a sure sign of impending doom. These are the noises that should be attended to immediately.
How can you determine whether the engine noises you are hearing are good or bad? From my years of troubleshooting diesels, I have learned the very best way to determine if the internal noises you are hearing are normal or not is to do a Diesel Purge. Let me explain. Most of the typical knocking and pinging in a diesel engine comes from injector “nailing” and ignition knock. When you run diesel purge through your engine most of these noises will disappear within ten to fifteen minutes. The lubricant in the purge will reduce the “nailing” or hammering in the injectors and the clean fuel will reduce the combustion knocking sound. I often wish I could run my engine on diesel purge all the time. The engine makes such a pleasant sound as the diesel purge is working its way through the pump and the injectors and “softening out” all those harsh sounds. (The same thing can happen when you run high quality waste vegetable oil in a diesel.) If the noise(s) you have been concerned about go away during a purge, then you can breathe easy. It’s very likely the cause of those noises can be fixed.
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Fuel injectors are the biggest noise producer in older Mercedes diesel engines. They will tick, ping, rattle and they can even produce a snapping sound. Nothing catastrophic can happen to your engine from this type of injector noise. In most cases, diesel purge will quiet all the noises related to your injectors and will soften up the knocking noise as well. If you diesel injector nailing or knocking noise comes right back after doing a purge, I recommend you rebuild your fuel injectors with the Monark nozzles available on this website. We offer a complete complement of tools and instructions to properly rebuild and pressure balance diesel fuel injectors in your garage.
On the other hand, If during the process of running the purge through your engine, the noise does not go away, then you should be concerned. You will need to look elsewhere for the cause of the noise(s). If a deep knock persists it could be serious and the car should not be driven until the source is determined. For more information on diesel engine noise diagnostics see my complete MANUAL