One last try on this problem...sounds like a loose valve but isn't.
 

I figured I would give this section of the forum a try before I give up on it once and for all. My '85 300 D turbo, CA emissions model, has a sound coming from the engine that sounds exactly like one of the valves are loose. I have checked, adjusted and rechecked the valves and they are all to spec. The "click" is engine speed related and seems to be louder when fully warmed up. Strangely, the sound can be best heard from the drivers seat. I have not been able to distinguish the sound from all the rest of the sounds that from under the hood with and w/o a stethoscope. I have checked for loose, broken or leaking items and everything exteriorly on the engine appear fine. The car otherwise runs good and has as much power as it should. The oil pressure and coolant temperature are both normal. I have run out of things to check and I would like to try fix this problem myself before taking it to a shop. Is there any technical expert out there that can help me?
~DJ

What do the timing chain/guides look like? Wonder if you are hearing the "kiss of death" chain noise? If it were mine and I confirmed that the chain/guides were good and it is running like it ought to I would just leave it alone:) and run it. Change oil every 3-5k depending on your preference and rack up them miles.

When I had the valve cover off to check and adjust the valves, I checked the chain at the same time and it appeared nice and tight. I wasn't really able to check the guides/rails at that time as I couldn't get a good look at them but from what I could see they looked OK. The sound that I have doesn't appear to be coming from the front of the engine as I would expect a bad chain or rails to cause. But I could be wrong as I can't really tell where the noise is coming from with my head under the hood. When in the drivers seat, it sounds like the noise is coming from the driver's side of the engine. When I stick my head under the car, it sounds as if it is coming from the bottom end somewhere. The noise started about 4000-5000 miles ago. I have since gone through a couple of oil changes and I haven't noticed anything out of the ordinary in respect to the oil with no visible metal particles before or after the noise started. Is it possible that the tensioner is bad and is there anyway to check and adjust it? How should the rails look and what would be a way to get a good look at them without having to tear the front of the engine down?
~DJ

I would also check the vacuum pump.

Our old 240D made a bunch of noises similar to what you are describing right before the vac pump disintegrated.

Haasman

Would it still work fine even if it was making noise and how long should it last? It's one of the last engine accessories that is still original.

lietuviai

>If< it is your vacuum pump and it is making the noise, it would work up to a point and then quit. How long ...... hmmm days? Hours?

Maybe it isn't mechanical .... if it sounds the loudest sitting in the driver's seat, check the firewall and see if there is a ripped grommet or seal or simply an opening that is allowing normal engine noise to reach the cabin.

Haasman

If that's the case, then maybe it isn't the vacuum pump since I've had the noise since last summer for about 5,000 miles or so.

That was one thing that I fixed just after getting the car back in March. I had some water leaks so I took care of any hole or broken seal that I could find. I think we can rule out any "normal" noises coming from the engine compartment.

Get a automotive stethoscope, I find them invaluable in finding wierd noises.
m

I borrowed one to check for my noise, it works as good as a wooden broom handle. Anyway, all the sounds I heard sounded the same, just a bunch of loud hammering varying in pitch and intensity. Those diesels are loud!

did you check the diesel injector unit out of curiosity?
m

Just a thought - could it be piston slap? I had a F#$D with a V6 that had piston slap (just out of warranty of course) - sounded like a tappet tapping - ran it another 60K miles before scrapping it. If it is piston slap - thicker motor oil will make it less noticable.

no one has questioned the exhaust manifold or the exhaust system.

is the manifold on the right side (pass)? being it is a calif car does it have a heat riser valve in the exhaust? exhaust leaks have a ticking sound not quite like a ball stud but it is engine speed sensitive

just my .02$

tks
craig

Do you mean the injector pump? How would I check it, since it seems to work fine. I didn't hear any noises coming from the IP. The injectors are another story. How could I check them?

I did check the exhaust system for leaks recently and all was good. That was one of the things that came to mind.

This had come to mind thinking of worse scenarios. I run Delo 400 which is a good diesel oil. I could try good ol' STP if that's still around. I remember using it years ago to quiet the lifters in high mileage gas engines and it worked good.

Run one of the good injector cleaners through it when I don't do this every few fill ups my SD gets louder..............
William Rogers.........

It was a shot in the dark sometimes the injector pump can make a noise and as it is tied to the rpm of the engine it will be in sync with acceleration and match your engine. If I remember correctly the vacuum pump is also right behind the injector pump, so either could cause the noise as they both are connected directly to the engine and will vary with engine rpm. The hard part is isolating the sound, I think you are on the right track there to fix this you are going to have to pinpoint the sound exactly, not easy on an MB diesel.

I ran two cans of LM Diesel Purge last Saturday with no improvement on the noise problem. I thought it was running better immediately after but I guess that was when it still had the diesel purge in the filter. It still runs the same which is good.

If it is in the IP or the vacuum pump, then I won't worry about it. These items will not be as serious as an internal problem if they should quit. An IP or v-pump won't cost as much as an engine to replace but an IP will still run a few $100 to replace.
Right now there is too much snow and ice to drive the 300D, so I'm back to driving my tried and true Tahoe and it'll go anywhere. The Benz can't get enough traction in the slush to keep the rear wheels from spinning.:(

I was in St. Augustine two weeks ago. I have had this annoying ticking or knocking noise for a long time. Anyway while I was there I pulled into a Mercedes garage a small independent shop. I asked the guy what it was. He said it was the vacuum pump. He said it was worn out and was causing this annoying ticking. He said he had changed many of them because of this. I will soon be changing mine.

My 2 cents

Dieselman

Interesting. Its worth looking into. I thought that since all my vacuum operated accessories worked fine, the v-pump was fine. When I was cracking my injector lines to see if the noise went away, it did or at least I thought so. Is it possible that when the car was running on one less cylinder at a time it was cancelling the noise in the pump? I'll have to check and see when or if my v-pump was changed. I wonder, how long is the pump supposed to last and is it worth rebuilding?

Consider a loose pre-combustion chamber might make such a noise.
Loosening the injector line could also identify this.
A friend discovered this in his 4 cyl a few years ago.

Is there a way to check the tightness of a pre-chamber? My guess this could affect the compression or cause some damage in the long run.

I thought it was a head-off job , Sorry it was a long time ago.

Maybe someone with a manual on CD can look it up for you.

Thanks, I have the CD FSM. I thought that there might be an easy way to check it.