Rattle noise at low RPM's - PeachParts Mercedes-Benz Forum

graysilm · #1 10-14-2008, 07:08 PM

I have just noticed a rattle noise when my tach is reading in the range of 750-900 rpms. I mostly hear the noise when I'm slowing down. It is a rattle sound that starts when i'm slowing down at about 900 rpms and cuts out at around 750 rpms. If I keep my rpms in this range the noise is continuous. The noise is coming from under the hood and sounds like its on the drivers side. Its not really loud, but definetly noticable if I have the radio turned off. My worst fear is that it is the injection pump. Does anyone here have any idea what could be causing this sound? Thanks.

TMAllison · #2 10-14-2008, 07:18 PM

Open the hood and operate the throttle by hand.

Common culprits would be the tensioner damper and the exhaust connection between turbo and catalyst.

graysilm · #3 10-14-2008, 07:48 PM

Thanks, I will try that tommorow. Speaking of the tensioning damper, I have heard that they have been problematic in some diesel MB's. Do you know if the 99's had bad dampers?

TMAllison · #4 10-14-2008, 07:55 PM

Its a little 6" shock. The pressed in bushings on either end can fail with age and cause a rattle.

John Graham · #5 10-14-2008, 11:02 PM

I have similar problem on '97 E300 non-turbo (210/OM 606/100 k). At between 750 to 850 rpm (just above idle) the engine starts to vibrate. As soon as the rpm goes over 850 the vibration stops and i'm unable to feel it at any other speed.
we looked at it on a lift rack . the only thing that appeared to be vibrating was the exhaust system, but all of the connecdions and brackets were good. The small vibration damper and belt tension arm was replaced recently. The belt looks good. The front motor mounts have been replaced. The rear mount and flex disk are firm. There is no noticable looseness in the water or steering pumps, a/c compressor or alternator.
I don't recall when I first noticed this it's been several thousand miles and it hasn't changed. Are there many of these cars with this problem? Any educated guess of the cause?

TylerH860 · #6 10-15-2008, 12:56 AM

I had a vibration at the same RPMs, the culprit was the air cleaner bracket.

TMAllison · #7 10-15-2008, 12:26 PM

Quote:

Originally Posted by TylerH860

I had a vibration at the same RPMs, the culprit was the air cleaner bracket.

The 606 is a completely different animal. Plastic air cleaner housing mounted on the firewall, etc.

The exhaust rattle at the joint mentioned previously sounds like a loose heat sheild. Per EPC there is fiber gasket in that joint. Doesnt make sense because it appears to be fluted type fitting. I'll take mine apart sometime to confirm if that is correct sometime.

Gray - If you do confirm the rattle is from the tensioner do yourself and favor and lift the engine 1/4" at the oil pan (NO more - use floor jack and big rubber bushing) and see if the sound goes away. If so, the problem is more than likely your motor mounts and not the damper.