I have a 1979 240 D that has started pinging ( like a gas engine does when it pre-detonates), particularly when the engine is cold. What causes this and what can I do about it? I recently switched to biodiesel, but it is makeing this noise when I switched back to petro diesel. Thanks.

 

It sounds like your injectors are "nailing," which is pretty common on these old cars. A good place to start is to run some diesel purge through your system. It's readily available on ebay, or better yet, mercedessource.com, which comes with a good set of instructions (you don't pour it in your tank, rather, you disconnect fuel lines and run in through the system).

It minimized the nailing on my current car (also a '79 240D) to the first minute or two of operation (it completely eliminated it on my old 300D). This would be a good place to start.

 

Thanks very much, I'll give it a try and report back the results.