My 1994 E420 with 150k miles, started and ran powerless and rough after standing for about 2 weeks. Ran fine before that. I had some rotten egg smell, but no smoke of any color. Also the water pump started leaking. I removed the water pump, and while waiting for the new part to arrive, I also removed all spark plugs, all looked nice and brown, except one that was black. Next, I did a compression test on the cold engine.

Cyl PSI
8 60
7 20
6 60
5 110
4 40
3 20
2 50
1 100

I read elsewhere in the forum that my compression should be around 200, but in any case there are huge differences and very low numbers by any standard. I checked the valve timing by inserting the pin into the right outer camshaft. the timing nicely lines up with the 45 degree mark on the harmonic balancer. (I reinstalled the old water pump and balancer for this).

Now I'm thinking it might be the head gasket, but it is unlikely that both sides blow at the same time. I don't know what I'm missing here, and I hope someone can help with some good advice.

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2004 E500 4Matic 138,000 miles