I have been working on my 1984 300SD (174k Miles) for the past six months and haven't had to post anything because the information is so comprehensive on this forum so thank you all so much!

However, now that I gotten rid of my coolant leaks, tuned the valves, replaced and reamed the glowplugs and got a hella glowplug relay and ran two diesel purges...

There is a knocking sound on cold starts and the engine seems to miss randomly till it clears after about a 30 seconds. I give it a little extra gas to make the shake a little less extreme, but it happens on every cold start. Idle is set to around 7k rpm.

The metal fuel line on injector 4 is starting to sweat. Does that mean the injector is clogging? I'm going to replace the metal fuel lines, but I would like to wait on replacing all of the injector nozzles, and I have not timed the injection pump and I do not know how much (if any) timing chain stretch I have.

I have seen a G wagon thread describing this problem, but after a diesel purge he just decided to live with it I think.

I was thinking of going to the junk yard and picking up some injectors and just replacing the one with the sweaty fuel line, just to see what happens. If I try this do I need to get a new heat shield wash or can I reuse the one that is currently on it?

I'm sure I will replace the injector nozzles eventually, but from what I have been reading 174K is a bit early for them to be having problems and I would like to put the job off.

When the car is warm I have absolutely no issues, but the shaking and missing and knocking when the engine is cold is getting worse. Thanks for your help!

Hi and welcome I believe your RPM should read 700. You make no mention of changing filters? Do you have the original prime pump? It almost sounds like when the car has been shut off for a period of time air enters your fuel. When you start it will run rough until the air has been bled from the system. You may wish to put the return line into a jar and see if you can detect any air bubbles under the same conditions you normally experience these issues.

I'm sure you will get a ton of advice here.

How did you come to believe your problem is caused by an injector....?
Have you loosened the fuel lines at the injectors one at a time to see if you can isolate the problem to one cylinder ?

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

I think if you got 150,000 miles out of a set of Injectors before the Nozzles were worn out that would be unusual. And that would if periodic Diesel Purges, the Valves are adjusted and the Fuel Injection Timing correct through out that time.

However, once the Cars are out of Warranty and especially after the Car is sold to some one else People seem to stop doing all of those things that keep the Engine Tuned up and that shortens the life of the Injectors.
Besides that the Stock Nozzles have some tiny drilled Passages that get plugged with Carbon. The passages are so small that once plugged solid with Carbon I don't believe a Diesel Purge will clear them.

On mine the Idle speed on the Emission Sticker is 750-800 rpms and that would be for a new Engine. Older Engines may need a little more.
If the idle rpms are too low the Engine is going to shake.

I just found this out about 1 month ago. I was troubleshooting a nailing on one Cylinder that was there till the Engine was 1/2 way up to the full operating temp and I eventually traced it to a Cylinder that had 50 psi lower pressure then the other Cylinders.

The Injectors and Glow Plugs were in excellent shape and I had recently done a Valve adjustment.

The reason for all of the above is that sometimes you need to make a list and methodically go down the list.

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84 300D, 82 Volvo 244Gl Diesel

I had a similar problem that was due to several related issues. Read this and see if it helps your problem.. Rough Starting Question

Good luck

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

Thank you for your replies!

I looked at the thread that psaboic posted, which describes my exact symptoms. I'm gonna look for bubbles in my plastic fuel lines and look for things to tighten in the other parts of the fuel lines.

My fuel filters are new and my primer pump doesn't leak, even though it is the old one. I will replace it soon though. I tried priming the system before a start and it squeaked on the first pump so I accepted that as being "all is well" with the primer pump.

I thought the problem had something to do with injectors because of the gray smoke that comes out. I thought that meant unburnt fuel, like from a dripping injector. I also thought the knocking sound had something to do with an injector from other things I had read. But it really does seem like an air problem.

And my idle is 700, not 7000, haha.

Thanks again for your feedback, I will post updates!

So I tightened some hose clamps under the gas tank and replaced the rubber and twine fuel lines between the injectors, no difference. My engine does have some blowby, if that effects anything. I'm going to ask my local mechanic mercedes guru tomorrow. If anything else occurs to you guys I'm still going to try and nail this down. Thanks!

Injectors where suggested to be checked for release pressure and spray pattern every 100K by the manufacturer of the car.

I would try another run through of the glow plug system. If you have a battery charger/jump box, you can bench test the plugs.....

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

I did check to make sure all of my glow plugs were getting voltage. I don't have a way to bench test them however. I called my guru about it and he thought it was injectors from the description. Could an injector be dripping fuel overnight when it not being run? If I start the engine and let it clear in 60 seconds, then I turn it off and start it again it seems to be fine. I don't think it's temperature related I think its time spent not running. I did increase the idle some and that helps with the shaking a bit. Thanks again for the replies!

Find the source of the fuel leak and fix it before doing anything else. Any leaks, no matter how small, allows air to get in and could be the cause of the problems you have.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked