Had a misfire on 6, 08 R350, P0306. Changed all 6 plugs and 6 coil, Now sometimes 4,5&6 misfires, but mostly P0300, P0305, P0306. new injector on 6. No change. Engine runs extremely rough with the belt tensioner hitting max (clacking). Swapped injectors 123 with 456, no change. Swapped coils 123 with 456, no change. The connectors look fine, nice and clean. What else can it be?

 

Post what codes you're having.

From googling M272 bank misfire, the short list of possible culprits are O2 sensors, clogged cats/exhaust, and balance shaft. Can also include vacuum leaks among other things, though less likely.

 

P0300, P0305, P0306

 

Check the above then. Honestly too many things that can cause an entire bank to misfire. A compression check can also give you some clues on where to look.

 

I'm digging in today. 4 is not reporting a mis. only 5 and 6. head gasket? Motor really bucks when running. Belt tensioner bangs, hammers, to the hard stop.
No smoke, would think a cracked piston would blow smoke.
Will pull the plugs, check compression and leak down on 5 and 6. Haven't done a leak down in 20 years.
How do you know the valves are closed on 5 & 6 without pulling the valve cover?
What else should I try, swap O2 sensors, Cam sensors, actuators?

 

WOW! 152K on the motor. #5 doesn't go up and down. It is up at the top, no longer connected to the crank.
#6 has no seal on the leak down. Putting air in the #6 plug hole and rotating the crank, intakes are not closing.
#4 is perfect on leak down.
What are the rods made of?
OK experts what do you recommend?

 

As I stated in the PM you sent me, you have some deep engine troubles if a cylinder isn't moving. At minimum you will need to remove the engine oil pan and check to make sure the crankshaft and connecting rods are intact.

 

I'll need to know the torques and sealant used for the gaskets. Is there a link or what should I google?
I can get a 2011 100K 350 for 2200$ . Can I get to the crank without pulling the motor? I'm experienced enough to know this will be a complicated and a stretch from working on an 80's benz.

 

The basics are the same. It's an OHV engine. You have the M272 family of engines. Do searches based on that and you should be able to find a lot of sources. The W164 (ML series) use the exact same engines as the R class, probably will be a lot more resources there.

 

Go to charm.li. has all Service ManaualManauas, diagrams!

 

Good site, thanks. Got the cam cover off, #6 intake lifter is off to the side explaining no compression on 6,

 

Thanks R3504Matic The torque specs are a big help. One problem. The head torque spec says 20, 40, 90 degrees, 90 degrees. Is that a total of 180?
The YouTubes I've seen do not explain or enumerate the torques and they all show just one 90. Does anyone here know for sure?