I have a 1997 E420 with 79K on it. It has a knock that sounds like it is coming from cylinder 7. Here is a link to what is soundl exactly like although it is not my car.
http://www.youtube.com/watch?v=Qeqm8d660yw
I have removed the covers and checked, rmoved, cleaned all of the oil tubes and they were all fine with no visible problems under the covers. I am also reading misfires on the obd2 reader from all cylinders on that head and the car idles and runs terrible.
I have changed the Plugs and only started and run it a few times since changing them. I just pulled them to do a compression test and they are pretty black with carbon. The drivers side seems much worse than the passengers side. I did the compression test with all of the plugs out and the engine was cold and this is The PSI I got on cylinders 1-8 respectively 204, 200, 209, 207, 210, 190, 140, 110. # 7 at 140PSI is the one I thought was noisy. What could this mean? Considering this along with the knock and miss problem it seems like it would rule out the Spark Knock or the catalytic converter because that would seem to affect all cylinders on that head equally. Could a stuck lifter cause the knock and the compression problem? How in depth is a valve job on these cars if it is a valve?
Thanks
Ben

A 79k mile 119 motor should not have compression numbers like that on 5-8. You might want to test them again to make sure. Could be a jumped tooth on the timing chain. Of course a 79k mile 119 motor shouldn't have that either but something is messing up that bank and it's not just electrical.

Would jumped timing cause those numbers on 5-8 especially 7 and 8? What else could cause this?

I have seen a 119 with the #5 piston skirts broken and the bore in bad shape making a knocking noise similar to the vid. With your compression #s going down front to rear it may be a lifter oiling problem caused by the plug coming out of the back of the intake cam on the 5-8 side leaking oil pressure from the lifter feeds. Check the intake cam to see if it still has that plug.

I repaired a 380SE that had a knock on #7. The intake mainfold gasket leaked coolant into the cylinder through the intake valve resulting in a bent con rod. The bent rod was just kissing the block and piston causing the noise.

Thanks for the replies
Can you tell me more about the cap on the camshaft? I am not familiar with what you are talking about but it does seem to make sense. I have heard that the bottoms of these engines are bullet proof and that the problem must be coming from the top end but the thought of it being the bottom of the motor really scares me. Thanks Again
Ben

The camshafts are hollow for oil to pass through them. There is a press fit plug in the rear of the camshaft to seal the oil in the cam. Sometimes the plug comes loose and oil pressure bleeds out of the rear of the camshaft. With your compression getting worse front to rear it seems logical that the pressure loss could be collapsing the lifters, with the worst ones being closest to where the oil pressure is being lost. Ie, #8 has the lowest compression and is closest to the suspected missing plug.

If the cap is loose or missing where does the oil flow to?
Thanks
Ben

It just flows out of the cam and finds the shortest path back to the pan.