I'm a first time poster. I haven't had a chance to review all of the postings in this forum, so if this issue has already been addressed, I apologize.

My 1999 E300 has been a very smooth, quiet, powerful turbodiesel since I purchased it about 15k miles ago. It now has 123k, and has always been very well maintained.

However, it recently began to make this horrible knock at any RPM above idle. It also now idles a little rough, but not terrible. Above idle, it sounds like a rod knock, but I believe it's unlikely to actually be a rod. I am new to diesels, but am pretty mechanical. I don't mind working on it, but I'm reluctant to just start tearing it apart and replacing stuff. Any ideas what might be causing this knock and rough idle? Both occured today.

Any assistance is greatly appreciated.

Bad fuel? If it just happened today it may be, but I know nothing about the new engines

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1981 300SD 512k OM603

Do you get any smoke from the tailpipe when it misbehaves?

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

If it sounds like one of the Seven Drawfs is in there trying to bust his way out with a ball peen hammer its probably a bad/fouled injector.

Should also look for any fuel leaks at the delivery valves on top of the injector pump.

*edit* if is an injector, you should be able to find which it is by touching the metal fuel lines with fingertips. Should be a noticable pulse that is stronger than all the others; if that doesnt work use your mechanics stethoscope or listen to the end of an 18" long screwdriver while touching different lines. Once you find it, pull it and have it pop/spray tested and adjusted; simply replacing the nozzle w/o doing a pop test does not guarantee it is repaired.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

At my old job we had two C7 Cats develop the same symptom. In both cases it turned out to be an injector that was sticking open and dribbling fuel in when it shouldn't have. The first one was kept running for too long before we figured it out and resulted in a destroyed engine. The second one we fixed a little quicker and we got away with a set of injectors-$3600 worth of parts, good thing it was under warranty.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

Just like you would pull (or short out) a spark plug wire. You can do a similar thing by loosening the fuel injection tubing nut at the injector 1 at at time (cutting off the fuel to that cylinder) while some one is in the car giving it enough fuel to make that sound (with the parking brake on and hopefully the person also has his/her foot on the brake).
When you get to the one/ones that are causing the problem that knocking sound will change/go away and note which one/s is causing the problem/s.
If you find something post here again for further advice.

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84 300D, 82 Volvo 244Gl Diesel

Can someone elaborate or re-direct to a thread that explain how "cracking an injector line" assists in diagnosing a faulty injector. Not to hijack the thread but also in hopes of further explaining/diagnosing how this procedure works and the original poster....

I know that my my OM606 there is at least injector that has been consistently nailing ever since I bought the car but clears up once warmed up. When just loosening the nut on the metal injector line at the injector, does that essentially shut down that cylinder and resulting in no new/current combustion noises?

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#dieselFLEET
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'97 E300
'99 E300

Correct. When the faulty inj is found, inj noise will be absent.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

Yes, you understand it. In a sense what you are doing is comparing the good injectors/cylinder to the one tha might have the problem. If all of your injectors are preforming well or the same; each time you crack open one of the injectors and "shut down a cyliner" you should get the same degree of negative resopnse for all of the good injectors. The engine would run rougher and ther RPMs would drop (nice to have a tach for this).
when you crack open the no good/poor injector there will not be as much of a change in the rough running or RPM. I short your engine will not miss the cutting off of the poor or no good injector as much as a good one.

Now all this being said the technique narrows it down to what cylinder is having the problem. It may not be the injector itself that is causing the problem and there could be something in the cylinder itself (low compression for instance could be caused by cracked rings or a burned valve could also cause nailing).
But from there you go by what is most likely to cause the problem or least expensive to check; the injector is easy to pull out and test as well as looking at the fuel injection pump for leak at the delivery valves.
That's why this forum is nice. Read enough and you will get an idea of what is most likely to be the cause of certain problems.

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84 300D, 82 Volvo 244Gl Diesel

This engine has a couple of items that can make a knocking noise, other than just injectors. I had a really obnoxious knocking from my serpentine belt tensioner when it died. I also had an alternator go bad and it would do something I still don't understand - I believe it had an internal short or something in the regulator that was shorting and it would periodically act like it was going to seize up, and make the belt tensioner freak out.

I have 162,000 miles on mine and have "eaten" two of those tensioners and one alternator. I presently have some delivery valve seal leakage, but no knocking. And as far as I can tell, I have the original injectors. I know they are the same as when I bought the car with 41,000 miles on it.

Good luck. If it isn't smoking or getting horrible gas mileage or using oil at an alarming rate, I would not suspect anything internal has gone wrong. Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

First of all, thank you all for your insites. My gut feeling, and hope, was that an injector had a problem. I will soon be pulling them all out. Which leads me to my next questions -

1. Do I need to purchase one of those special MB Injector sockets to remove the injectors, or can I just use a 27 mm deep socket?

2. Also, is it necessary to remove the intake air plenum before removing the injectors, or can they relatively easily be removed with the intake plenum in place?

Thanks much for your assistance.

Go to this site and check the socket specks it is 22MM!!!!

http://www.startekinfo.de/etools/content/tool.jsp?toolno=606%20589%2000%2009%2000

Also: Correct injector socket for 99 E300D OM606

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84 300D, 82 Volvo 244Gl Diesel

If this is what your injector looks like measure from the bottom of the wrench flats to the top of the injector to see how deep of a socket you need.

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84 300D, 82 Volvo 244Gl Diesel

You need the 606-0009 socket from the special tools tab under BUY PARTS above.

http://www.peachparts.com/diy/mb_tools/mb_tools.php?page=19

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

Hi,

Does anyone know the exact length of this 22mm socket ? I have found one that measures 4.25"....is that long enough ?

Thanks in advance !

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1987 560SL - 95K
1996 E300D - 183K
1997 E300D - 162K
1982 240D - 160K