I wish I could listen to other 603's to see what's "normal". The truth is I've been battling what I've thought to be a knock on my 603 for almost a year and I haven't won. Shortly before I rebuilt my injectors there were occasions when there would be no knock. Afterward it's been constantly there just like when I first bought the car. The only time the engine sounds totally smooth is when it's running on Diesel Purge. My question is, does your 603 knock? Or does mine really have some sickness?

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

FWIW, mine knocks constantly. It's worse after a cold start and less after a good highway run. I'm not worried.

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2001 Dodge Ram 2500 Cummins Turbo Diesel - 4x4, auto, 3.54 gears, long bed
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'92 300D 2.5 Turbodiesel - sold
'83 300D Turbodiesel - 4 speed manual/2.88 diff - sold
'87 300D Turbodiesel - sold
'82 300D Turbodiesel - sold

That seems to be your answer right there. The fuel you normally use might be low quality. In any case, it won't be as good as Diesel Purge (mostly diesel right?). Has to do with cetane ratings. Just like you can get funny noises from gas cars when you use low quality fuels.

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Stefan Neu

1982 300sd ~170,000

None of the four 603's in my family "knock", except the normal diesel klatter when cold started. When warm, they sound like industrial sewing machines, especially above idle speeds. MUCH quieter than any 617. Could be a lifter noise, try running Mobil-1 synthetic if you aren't already (15W-50 or 5W-40 weights only). Wouldn't hurt to check the chain stretch and IP timing, just for grins, if you never have done this...

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Dave
Boise, ID
Check out my website photos, documents, and movies!

No mine never knocks, the lifters just keep right on ticking. Did you check the shock that tensions the belt? I have heard they can make some mechanical sounding noise when they go south. On a side note when my lifters are quiet it sounds the way GSXR described it, I can't wait to change my lifters.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

the knocking in mySDL gets worse when it is hot. not sure if i should look at injection or buy syn oil to quiet up a lifter... it starts and sounds great when its cold. but lately at hot idle its getting a pretty good shake in it. like DieselAddict i wish I could hear a properly tuned 603.

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sold
1987 300 SDL 318K
126.125 (OM603.961) (722.321 trans) (head#14)
Born on date 11/07/1986
2.5" Flowmaster Exhaust
flex-a-lite dual electric cooling fan conversion

now have a 1985 toyota diesel pickup

I do use M1 15W-50 and my belt shock is new. Since the engine quiets down when running on diesel purge, I'm sure the noise is not related to lifters. It definitely does seem related to the cetane of the fuel, but I don't think it should knock that much even on regular fuel, since my other 2 cars don't do that. It only does that at idle though. Above like 1500 rpm it's totally smooth like a gasser. I have not checked the timing chain, partly because the car only has 153K miles.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

Time to check:

1) Chain stretch (just to rule this out)
2) Injection timing (start of delivery)
3) I'd pull the injectors and have them pop-tested, and make sure they are all within 3 bar of each other - out-of-box rebuilts can be WAY off
4) Might want to consider at least visually inspecting the installed prechambers, if not removing them for complete inspection (possible damage?)
5) Something amiss with the injection timing device that advances timing with RPM (?? Hard to test this w/o dealer equipment)
6) Leaky delivery valve seals? (grasping at straws here)

The knock would seem to be incomplete combustion. My car is NO quieter running on Diesel Purge than it is on normal diesel fuel.

BTW - does the noise go away completely above idle speed? My cars make a light diesel sound at idle, but it's quiet. This goes away around 1000-1500rpm. If it sounds like you have a bucket of marbles rattling around at idle, though, that's too loud. Any chance you can find another 603 to compare to? If it's as noisy as a 617 at idle, that's not normal...

I sent the question to Marshall (MBCA Diesel Tech Advisor), here's his reply:

Well, It's surely combustion knock. That's evident if the knock goes
away when using Diesel Purge with it's MUCH higher Cetane rating. The
kind of noise he's describing is what Mercedes spent 50 years quieting
down so that diesel engines could be used in passenger cars! The noise
or lack thereof is largely a function of the size, shape condition of
the prechamber, the injector geometry and spray pattern. A perfectly
running Ford Power Stroke or Dodge Cummins diesel at idle sounds like
someone is shaking a jar half full of marbles. They have made little or
no effort to quiet the combustion knock. Anything out of order in the
prechamber will cause the problem.

If it can't be quieted using the usual injector cleaning, spray pattern
and pressure inspection and Italian tune-up regimens, then removal and
inspection of the prechambers for damage would be next.

Leaky delivery valves or valve seals CAN cause such a problem, but they
fail MUCH less often that any of the other things that could be wrong (I
have had one fail - once - some 35 years ago). There is no simple test
for this - only test requires removal of the pump and testing on an
injection pump test stand. Usually when the delivery valve is bad, the
knock will not quiet or not quiet much as the engine is loaded, while
most other causes the sound WILL diminish as the engine load increases.
This is NOT a definitive test, but is suggestive.

Marshall

DieselAddict, my '87 300D turbo had knocking noises esp cold. All new lifters and a new timing chain fixed that. If I ever get up to Reno I'd enjoy giving you a listen heck even a test drive. The OM603 is really quiet (as diesels go) at idle when running right.
BTW, could 10% Bio have any part in the noise? Try adding some redline Diesel Catalyst to see if that helps.
DDH

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

My 87300DT used to nail until I removed and cleaned all injectors and purged the system. Since that time, I have discovered who still was selling winter fuel and when they finally got their first summer fuel, my engine began to nail a little. I always put either RedLine, or Power Services, cetain boost and like GSXR, my 603 runs pretty quiet, you can hardly tell it's a diesel!

Of course now I have to do a head gasket, so it's off the road for a little while!

If it only knocks at idle, say between 650 - 1100 rpm, then it is probably the belt tensioner shock. Just had mine replaced and what a difference. Almost as quiet as a gas engine. Well not that quiet, I guess!

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Paul 1987 300 SDL; 2000 ML; '69 MGB; '68 VW Fastback

Hard knock and rough idle that goes away at high rpm sounds like leaking delivery seals to me -- this is very likely true if someone messed about with the IP before!

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Thank you people for all the responses so far. In the past using fuel additives had a very small if any effect. The B05 did seem to help and eventually the engine was quiet most of the time when warmed up, but sometimes it would still knock so I decided to rebuild my injectors and open a whole can of worms. Because of the indian nozzle saga I ended up reusing the old nozzles, but I did balance the injectors to within 3 bars and in the end all seemed to spray good with no squirting. However I accidentally dropped a little bit of the crud that had built up around the injectors into the prechambers. I know this isn't good but wouldn't it get blown out after a couple italian runs? Anyway ever since I put everything back, it has been knocking just like before I started using B05, maybe even slightly louder, but the car runs very good. Good acceleration and no shaking at idle except the occasional few hiccups after a cold start.

I'm attaching a zip file with 2 sound files in mpeg format that I just recorded in the garage with the car windows open. They are small files because they're just one frame and all sound. Let me know what you guys think.

Attached Files

603sound.zip (62.9 KB, 570 views)

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL