What causes rythmic running? - Page 4 - PeachParts Mercedes-Benz Forum

LJetronic · #46 10-30-2008, 10:54 PM

My 86 sdl exibits the same phenomenon. I've always just thought it was an exhaust issue. I had an old 280zx (2.8 inline 6 gasser) with a bad exhaust system and it had a very similar sound. I think it just might be the way the engine sounds!! I will say that my car has a motor mount issue, although they look good and are not collapsed at all, the car rattles quite seriously at idle, especially when cold. I guess my mounts are getting hard. Perhaps this could be amplifying the sound by more rigidly transmitting the sound to the body? Ive just accepted the droning harmonic sound as the particular sound of the 603. Especially since others are experiencing similar sounds makes me more at ease!

babymog · #47 10-30-2008, 11:04 PM

I agree.

It's quiet enough that you have to have the windows up, ACC blower on low, radio off, ... but around 2kRPM you get this 2hz "beat" that is evident up to around 3K, just have to be quiet enough to hear it. Can't feel it, just hear it. Engine speed, not car speed dependant, so it's from the TC forward. Sounds like a twin-turboprop slightly out of sync.

jpjp22 · #48 02-05-2009, 03:34 PM

I know this is an older thread that was revived once already but I came across it in searching for "resonance".

It's nice to know that it seems to be a common sound and probably not an issue.

BTW, I don't always notice mine ('86 300SDL) but when I do it's around 2800-2900 RPM and it seems more constant if you hold that RPM level. I have never noticed it pulsating, although I guess it's possible. I usually just push it on up to 3000 or 3100 and it goes away (or have the radio on and you don't hear it).

Did anybody ever figure out what causes this noise?

80's old school · #49 02-05-2009, 04:27 PM

I have a sound!!

Look here!! This is the exact sound that I seem to have on my 123! I posted about this in early January. People thought it was the tires....I kept thinking NO...