Noise from engine 617.952 - PeachParts Mercedes-Benz Forum

Gordo · #1 10-05-2007, 02:10 PM

I did a search for engine noises and could not find anything like this. I don't have the technology available to let you listen, so I will do my best to describe it.

Background:
I notice it only above 2000rpm and only when the engine is warm. It is most noticable under deceleration, probably because there is less other stuff to cover it up. It is slowly getting louder as I drive the car more. This is a daily driver. I commute about 30 miles in the mountains at hwy. speeds. The first hints of the sound started about a month ago.

Description:
Scratching, metallic sound that is intermittent. It comes in short intervals about .5 sec every 1-2 sec. It sounds a little like snow studs on a dry road. I hear it best from inside the car, although I can reproduce it with the hood open by revving the engine.

I have also noticed a slight loss in power. Perhaps just my immagination.

Thnks for all the good advice.

rrgrassi · #2 10-05-2007, 02:11 PM

Have you adjusted the valves yet?

DieselAddict · #3 10-05-2007, 02:15 PM

Sounds like a bad injector. They typically show up as a pinging sound under light load and moderate RPMs. Valve adjustment is routine maintenance and should be done regardless of engine sound.

rrgrassi · #4 10-05-2007, 02:18 PM

Ford RattleSmokes sound like that all the time under light load.

The pinging sound is also called nailing. How many miles are on the car? When was the last time the injectors were pop and pressure tested?

Gordo · #5 10-05-2007, 02:22 PM

I don't think it is valves. I adjusted them about 8000 mi ago. Timming chain strech was a little over 2 deg. I will go through them again. By "snow studs on a dry road sound" I mean a scratching like a car going past at 40mph not snap and pop 5mph

rrgrassi · #6 10-05-2007, 02:26 PM

Under the hood, where does the sound seem to come from?

My A/C compressor that lost it's clutch bearings started out like that when the compressor was off, then it did it all the time.

Also check the alt bearings, the water pump, power steering pump, and the vacuum pump

Gordo · #7 10-05-2007, 02:28 PM

Quote:

Originally Posted by rrgrassi

Ford RattleSmokes sound like that all the time under light load.

The pinging sound is also called nailing. How many miles are on the car? When was the last time the injectors were pop and pressure tested?

265,000mi. on this motor (from the yard) never tested injectors. Although I will try cracking the inj. lines to see if I can trace it to a cyl. I am more concerned about timming chain tensioner/guides, vac. pump or SLS pump although I can't seem to trace the sound.

winmutt · #8 10-05-2007, 02:30 PM

Since I am from down south I have no clue what snow tires sound like

..

Any chances it your air filter mounts? Try cracking each injector and attempt to reproduce it. How are your belts?

Gordo · #9 10-05-2007, 02:33 PM

Quote:

Originally Posted by rrgrassi

Under the hood, where does the sound seem to come from?

My A/C compressor that lost it's clutch bearings started out like that when the compressor was off, then it did it all the time.

Also check the alt bearings, the water pump, power steering pump, and the vacuum pump

No AC. I took it off. Water pump is not leaking. It seems like it is comming from in the motor I will check my alt. I will do a search on checking the vac. pump.

rrgrassi · #10 10-05-2007, 02:39 PM

See if you can isolate it to the front of the engine. There was a post on this site IIRC, where a loose alternator was making a noise that made the owner think it was a probelm with the engine. Belts were tight, but the alternator hold down bolts were loose.

Gordo · #11 10-05-2007, 02:51 PM

Quote:

Originally Posted by rrgrassi

See if you can isolate it to the front of the engine. There was a post on this site IIRC, where a loose alternator was making a noise that made the owner think it was a probelm with the engine. Belts were tight, but the alternator hold down bolts were loose.

Alt. is solid. I can't seem to make it wiggle at all. Belts are good.

Could be front of the engine... or deep in the engine (Oh dear... I hope not.)

winmutt · #12 10-05-2007, 03:24 PM

Vacuum is ok? Pull the valve cover and look around. Might not hurt to drain oil and look for metal. I would crack the injector lines first. What about the fan coupling?

rrgrassi · #13 10-05-2007, 03:25 PM

Check all the simple stuff first, like vacuum pump, etc. A mechanics stethoscope would be helpful also.

When were the engine mounts and shocks changed out?

chetwesley · #14 10-05-2007, 03:44 PM

This might have been me. The bolts that actually hold the alternator together (not the ones that hold it onto the car) were loose and rattling around, though I mainly noticed that at idle, and occasionally when I drove past something and could hear the sound reflect back.

Quote:

Originally Posted by rrgrassi

See if you can isolate it to the front of the engine. There was a post on this site IIRC, where a loose alternator was making a noise that made the owner think it was a probelm with the engine. Belts were tight, but the alternator hold down bolts were loose.

t walgamuth · #15 10-05-2007, 05:52 PM

I suspect worn cam chain tensioner or vac pump. If it is the vac pump you don't want to tarry in fixing it. It can trash the engine if it comes apart and parts fall into the chain and break it.

The cam chain tensioner is nothing to fool with either.

Tom W

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