Misfire on 5 & 6
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560sel,250sl,c320,c43
Misfire on 5 & 6
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?
Last edited by Garyman; Dec 21, 2023 at 01:16 PM.
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Joined: Nov 2017
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From: San Francisco Bay Area
2006 R500
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.
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.
Thread Starter
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Joined: Mar 2011
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560sel,250sl,c320,c43
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?
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?
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560sel,250sl,c320,c43
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?
#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?
Super Member
Joined: Nov 2017
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From: San Francisco Bay Area
2006 R500
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.
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560sel,250sl,c320,c43
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.
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.
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Super Member
Joined: Nov 2017
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From: San Francisco Bay Area
2006 R500
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.
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From: Dallas, TX
2006 R3504Matic, S430, BMW750E66, E350 207, PORSHCE 911C4S, BMW128 E88, VWTREG, 86 560SL, 88560SEL++
Service Manual R350
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.
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.
Go to charm.li. has all Service ManaualManauas, diagrams!
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560sel,250sl,c320,c43
Putting the M272 back together
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?
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?
