My 1994 Mercedes E320 wagon has this loud motor sound and where does that loud sound comes from? Is it the exhaust, manifold, catalytic converter, muffler, losing compression, defective 02 oxygen sensor, etc? There is no check engine light (CEL) showing. However, on the self-diagnostic test (DSM) 16 pin, it shows the troubleshooting light of 4 only, meaning the MAF sensor. I had this issue of MAF for quiet some time but I don't think it is related to the loud motor sound.

When I started the car the first time, at first, normal, then driving a short distance and of all sudden loud noise coming from the engine? I cannot pin point the exact location of the loud sound. It sounded like a hot rod.


I do notice a difference in the rpm on the dashboard. When I floored the accelerator, normally the rpm at around 4400 would rattled which is normal. Now the rpm is free floating over to the maximum without rattling. Is it a rpm issue? If so, what would be the culpit? I am somewhat baffled by this issue and scratching my head as to what is the source of the problem. Any ideas anyone? I appreciated some feedback on this issue. Thanks.

Correction on the DSM above, it should be DM (diagnostic module) and quiet was misspelled for quite as in quite some time mentioned above. Sorry about that.

If it is a roaring sound it may be a fan clutch that is locking up early. When the noise occurs pull off the road and put the car in park, rev the engine and see if the noise is present. If yes see if it seems a though the fan is pushing a lot of air. Stay clear of the fan blades. I don't think it is exhaust or transmission because they would make the noise all of the time.

If you do replace the fan clutch, research which brand to purchase. Members recommend one brand in particular, I think it is Sachs???

Good luck and keep us posted!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Thanks for responding. I appreciated it. However, you are correct with fan clutch issue because I had that problem before and replace a new fan clutch. The fan clutch is not the issue. I should have mentioned earlier in regards to the above first statement when I wrote first start the motor then the noise kick in. Since then, the noise is always there, even when I start the motor. However, you gave me an idea that if I remove the serpentine belt and start the motor and if the noise is still there, then it means some internal part of the engine is the issue and not other parts that relies on the serpentine belt such as alternator/generator, fan, air compressor, power steering pump,etc. I will follow up on this.

Try unplugging the AIR pump on the passenger side if it has one to see if that changes anything. The pump comes on for about thirty seconds producing a fluttering air sound and then should disengage.

Also when you disconnect the serpentine belt roll each pulley by hand to check for noisy/loose bearings.

Good luck!!!

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Are you referring to smog air pump as you mentioned above in your post

My friend found the problem with the exhaust loud noise issue. It turns out the sleeve goes inside the exhaust pipe that connects to the middle/front muffler was cracked and some of the areas of the sleeve had some holes as well. Both mufflers are fine. He removed the sleeve by prying with the screwdriver, hammer, and plier. I bought a new sleeve that matches the old one along with new clamp. He also has to weld the sleeve into the hole of the front/middle muffler. Also, the exhaust pipe that is connected to the rear muffler was bent due to dragging. He had to bend back to the original shape so the sleeve will go inside the middle/front muffler. Total cost was much much less. The only replacement was the sleeve and new clamp.