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What is this sound?

2K views 18 replies 6 participants last post by  Patman1 
#1 ·
I feel like my engine is making this odd sound, almost like it's now a diesel? Or just has a fluttering noise in idle and when I rev the engine. The car is a C230 2000 Kompressor has 83,000 miles on it. Oil change recently and tranny fluid changed recently. No significant mods to car.

Any help would be appreciated!

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#5 ·
Thanks for replying! Excellent help, and I did take a look at the entire exhaust set up. It's all OEM and doesn't seem like anything is wrong with it. The tensioner you're mentioning where is its location?

Thanks again for your help! Sorry I'm pretty new to working on my own car..
 
#7 ·
In my experience, the lever and the axle bolt are what wear out. I'd replace the entire assembly - in fact, I've had to.

Fortunately, it's not that difficult on the 4-cylinder engine.
 
#11 ·
The tensioners on this car are the more modern metal spring type and tend to last a long time. The older type with rubber bushing and lever arm on the older M104 engines were more touchy and a lot of replace parts were crap. If the belts are still tight, they are probably OK. You have an idler pulley and a tensioner pulley. Either one of them can need replacing. Remove belts and spin everything to see if there is any noise. Tensioner shock is a common source of noise when they get old. You can test it by pressing on the top bolt with a big screwdriver or pry bar while engine is running. The top bushing gets old and shrinks and starts to rattle. If it settles down when you push on it, it needs replacing. Noise is particularly loud at startup.
 
#13 ·
regarding the tensioner glenmore has said all you need. the noise does sound like my car did with a bad tensioner.

if you are recording from the rear, and if it is the tensioner, then that is one loud sounding busted tensioner/idler.

how does it sound in the front?
 
#14 ·
Febi is hit or miss, probably mostly miss. Meyle makes decent parts (I'm going to get shit for saying that, but from experience, they are good parts). Stay the @#$% away from URO. Lemforder and Corteco are brands you can blindly trust. But honestly, check the dealership, many times I have gone to the dealership and they gave me very decent prices. Sometimes cheaper than buying online if you counted the shipping. I guess the only reason not to buy genuine parts is if the genuine part has some flaw in it that an aftermarket has solved. Keep in mind, mercedes doesn't make most of their parts, 80% of your car is made by Lemforder and Bosch, so sometimes the better deal can come from shopping around.
 
#15 ·
Okay so I bought a Litens drive belt tensioner because I felt like that was the problem, but as I further inspected the car I realized the sound doesn't seem to be coming from the tensioner or pulley system. Instead it seems to be coming from the upper right middle portion of the engine itself. I've got a video. So I'm thinking I may now have bought the wrong part...

Thanks for more feedback!

 
#19 · (Edited)
It's really hard to say where the noise is coming from. If I were to bust out the weird noises mental diagnostics flow chart pocket edition, it would go something like this:

The M111 engine is actually pretty damned bullet proof. I would rule accessories first. My first case is this noise is coming from the supercharger. If you can have a buddy rev the engine a little bit, check to see if the noise starts when the supercharger clutch kicks in. The superchargers on various M111 engines are known to break (bearing issues, I think they are rebuildable). The sound may not seem like it's coming from there, so look for the visual cue of the clutch kicking in first. All the noises coming from an engine bay sometimes makes it hard to pinpoint one exactly. Since you don't have a check engine light, this is a good place to start.

The belt tensionner is pretty sturdy as well, but the idler pulley that bolts to it isn't. Wonky idler pulleys make so many weird noises they can probably account for the wow! signal. The best way to diagnose this is to take the belt off and spin the pulley by hand. If it spins freely, it's bad. It should have a lovely resistance to it, and no axial/radial play (you can check all your other pulleys that way while you are at it).

The next source of noisery on the M111 is the adjustable intake camshaft. It sounds like the noise is starting around 1500rpm, the same time the intake camshaft goes to full advance. Test this by unplugging the camshaft magnet, located under the plastic cover in front of the engine. This might trigger a CEL but if the noise goes away, you need to replace the intake camshaft sprocket (the magnets usually are fine but you might want to consider redoing the oil seal on it, they can leak with age).

Also, I don't know about any secret things going on in the middle of the engine as MB-W202 claims :D but hey, maybe I'll get an internship at google and I'll move to california.
 
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