I recently bought a 93 300D 2.5 Turbo with 110000 miles on it. I've now noticed that the engine has considerable knocking, and smoke at idle. The inline fuel filter was the most clogged i've ever seen a filter before, so I would imagine the main one was shot as well. Replaced both, still knocking, smoke, etc. Also noticed that the inline filter is NOT completely full of diesel when running which seems odd, because my old 300 SDL would have the filter full of fuel. What is causing all of this? This engine starts perfectly in 10 degree weather or even colder, by the way.

Also, we cleaned the engine and the entire compartment at a car wash, (so the engine + compartment was completely wet, could this have damaged electronics?) also had all fluids changed. Before we did this, everything worked just fine. Now the turbo doesn't feel like it's boosting, transmission shifts hard, and there is no AC or air flow through the middle two vents. While we were getting all of the fluids changed, the guy doing it was messing around with the air filter. I know there are a lot of vacuum lines, transducers, and electronics around that area. Could this have caused it?

Where do I even start?

Help would be very much appreciated!

That sounds a lot like a vacuum line got knocked loose....

A vacuum line off will cause the HVAC problems and hard shifting. Knocking and smoke at idle, I don't know, but some have said that spraying water on a hot IP can cause internal damage, sounds somewhat more like the fuel system might be sucking a bit of air.

I've never tried it, but it seems that a fuel line from the injector return into a glass jar should not have any bubbles coming out.

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Gone to the dark side

- Jeff

A loose, or off vacuum line seems that it would solve the turbo, transmission shift, and AC issues. What lines would I need to check first? So i don't go digging around aimlessly.

well.. all is the right answer.

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1996 s10 zr2 with a 6.5 turbo diesel
1996 c2500 suburban with a 6.5 turbo diesel
1981 300sd with a turbo 617
Monte carlo figure 8 car

Center front of engine where they come off of vacuum pump. Some go right to the tranny ip and vents. Some go left to egr and god knows what. Start at vac pump and should be close tom that split or over by air cleaner.

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What Would Rudolph Do?
1975 300D, 1975 240D, 1985 300SD, 1997 300D, 2005 E320 , 2006 Toyota Prius

Thank you for the tip! I'll have to go check all of those lines. Maybe the people who changed the oil underneath the car knocked a line lose, or something.

Interesting note.... Put half a tank of Biodiesel in the car, and the engine is running as smooth as I've ever heard one of the diesels run. Absolutely no sign of nailing, or knocking! Perfect MB diesel idle.