1983 240D

The car sat for just about a week, and when I started it up this morning it had a slight knocking sound. Hard to tell if it is coming from the injectors, but that was my first idea. I checked the oil and topped it off just to be sure. When I put it in Reverse the knocking went away. Put it back into Park and it was still there.

Something I've noticed since I changed the filters out last, is that the inline filter always has a slight amount of air in it. The hose that feeds into that filter is a little old, and I've always meant to change it out. Do you think it could be drawing air through that hose and causing this knocking sound? I had my wife drive the car to work, and she said it wasn't knocking after it warmed up. Would appreciate some ideas from you all.

Mysterious noises that come and go all by themselves are not that unusual with these cars. Since your car was sitting for longer than unusual it might just have been something that was slow to oil up properly and start moving freely.

Once upon a time I thought my flexplate was going out on the 77 300d perhaps. The noise lasted for a short time and dissapeared never to return. It evoked mixed feelings at the time.

In one way I was happy yet on the other hand how could the car have managed to do this? The noise was quite pronounced.

About the only thing I could think of in hindsight was that the starter drive had not retracted fully just the one time. Really though I was unsure of what it was other than its general location at the back of the engine. Maybe you heard an injector knock? They have been known to come and go I believe.

At least your car was out of service for a little while. Mine was in daily use at the time. Your knock was not deadly serious or it would have not left.

I also guess that if it returns you could back off each injector trying to locate the offending one and maybe have it checked. Or exchange it with another cyllinders to verify it is indeed that injector.

Thanks for the reply. Sounds like a good idea. If it happens again I'll try to loosen the lines to the injectors individually to see if it goes away.

Do you all have air in your prefilter? I don't remember there being any air in there when I first purchased the car.

There will always be a stationary bubble present unless the filter is perfectly vertical I suppose. Just a little air trapped in a higher pocket.

As long as there is not a visually transiting or flowing stream of air bubbles all is well.