I need some input. 163K miles, has what seems to be, a miss. I have done the following: changed injectors, replaced all filters, removed harmonic balancer, removed and cleaned intake (filthy), removed and cleaned exaust manifold, checked turbo (fine), replaced injection pump, checked blow-by, has good compression (310 balanced), has good power, does not smoke, adjusted valves, nothing has had any effect so far. I'm getting ready to remove the pre combustion chambers to have a look. Does anyone have any suggestions?
It is more noticeable at about 900 RPM and there is a slight rumble @ highway speed, (60-80 MPH). More annoying than anything. Kind of rocks at idle and has a chug-chug sound beginning @ about 900 RPM.

Bob

 

If you do not have one I am selling a tool for removing/installing the Pre-combustion Chamber Lock Rings and also the tool to pull the Pre-combstion Chamber.

I think you will need to give more info on your trouble shooting.

Did you replace the Injectors with rebuilt ones?

Were you able to isolate any particular Cylinder as the cause of the miss?

I am not seeing in your list of things you have done that you did a Valve Adjustment.

Have you checked your Camshaft Timing to check your timing chaing stretch and Timing Gear Wear. (With number one Piston coming up on the compression stroke carefull align the Camshaft Drive Gear Timing Mark with the Timing mark that is on the #1 Camshaft Tower; and look down to see what degrees on the Crank Damper the Timing Pointer Points to.).

 

Below is a split pic of my Camshaft Timing.
Left is the timing marks lined up and to the righ is the Pointer showing that I am between zero degrees (zero degrees is top dead center and where the Camshaft was timed when the Engine was built) and 1/2 way to the 5 degree mark; meaning the I have about 2 1/2 degrees of late Camshaft timing.
The causes of this are stretch/ wear in the Timing Chain and Timing Gears.

For the above test to work the Timing Marks have to be aligned exactly.
If I had found that my Timing was late something like 6 degrees. I would do another test that is more precise called the "2mm method". This would precisely determing the exact degrees.
After that I would decide if I wanted to replace the Timing Chain or use an Offset Woodruff Key (from the Mercedes Dealer) to compensate for the Timing Chain Stretch.
After the Above the Fuel Injection Pump would need to be re-timed.

I never ask in my previous post how you timed your replacement Fuel Injection Pump; what method did you use.

 

Valves have been adjusted, cam timing is correct. I replaced the injectors with known good injectors from another car which runs well. The injectors from the problem car were installed in donar car. Donar car runs great, problem car stiil had the miss. I was not able to isolate the problem to a particular cylinder. I'm sure it's one cylinder as there is no smoke, has good power and gets good mileage. Cracking the injection line nuts produce the same result on all cylinders, as soon as the nut is loosened, it misses really bad. The miss that the engine has is not that pronounced. Timing chain and sprocket are good, that is to say, not stretched or worn. Timing marks line up perfectly. I didn't do the injection pump myself, a Mercedes mechanic did it, I'm sure he used the 24 degree/drip. Old and replaced pump gave the same result. I'm going to try puting a bore scope into the precombustion chamber to look for any abnormalities.

Thanks for all your advise. Any other suggestions?

Bob

 

I cannot think of anything right off and also have not read of anything like this before.

I used to be a Diesel Mechanic but not a Mercedes Mechanic.

as you said the response from the Injector cut off test showed that the Injectors are good.
The Compression test showed that the Compression is good; Cylinders+Valves.

Thoughts:
A Valve was not seating intermittantly could cause a miss and maybe not show up in the compression test.
The chugging at 900 rpms could indicat a problem with the Engine Timer advancing inproperly. If so yours would be the first case I have read off this happening.

Since it is easy to do I would get my 2.5 liter spare Fuel Container with clean Diesel Fuel and remove the fuel inlet hose and install a longer one running to the Fuel Container and see if running on the Container changes anything.
This would bypass and fuel supply problems from the thank.

I know you have done some of this stuff but I had that Rocking at idle when the Engine got up to full operatint temp.

I bought that updated Gold Colored Rack Damper Screw but it had little effect.

Rebuilding the Injectors (I did this myself) too away bulk of the Rocking.

Valve adjustment took away the next largest cunk of Rocking.

Replacing the Motor Mounts and Transmission mounts took away some more. (I replaced one of the Engine Shocks and both Shock Mounts but with used mounts.)

I had a small Air leak at my too hard Fuel Inlet supply Hoses that showed up only when the Engine was hot.

Finally that Rack Damper Screw was able to be adjusted to take out some more Rocking.

 

One possible for the rumbling sound at highway speeds is the Drive Shaft Support Bearing.
You might have someone else drive the Car while you sit in the back seat and listen and see if you can identify where the sound is coming from.