Need help diagnosing probable cause of the S500 running rough, shaking quite a bit at idle, it drives at normal speed but rough. Stop by a local AutoZone to get a quick diagnosis and the following troubleshooting came up: (using their scanner)
P0442
Definition:
EVAP (evaporative emission system) small leak/no flow condition.
Explanation: The evaporative emission system is monitored for its ability to hold vacuum.
Probable cause:
-defective or loose fuel cap
-EVAP canister or hose cracked-not connected
-Purge or vent solenoid defective
-Vacuum leak at engine

P0308
Definition:
Cylinder misfire detected-cylinder number 8
Explanation: The powertraincontrol module monitors the crankshaft speed and has detected a misfire condition
Probable cause:
-Ignition system fault-spark plug(s), ignition wires, coil
-vacuum leak
-injector fault
-high or low pressure

I would like to attempt to hopefully solve the problem before I have to take it to the MB dealer for a diagnosis.

Can anyone familiar with the S500 V8 can tell me the cylinder order, when standing in front of the engine (attached pictures)

All the help will be appreciated

Bluerio

Attached Thumbnails

     

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Bluerio

w/o SDS you can't run the proper tests on the EVAP to nail down the problem...

As for cylinder number 8, check the plug. Move the coil, see if the misfire follows the coil or stays with the cylinder.

When was the last time you did plugs? If it's been more then 20K I'd go ahead and replace them just to be Sure.

Jonathan

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Blue Ridge Mercedes
Jonathan Hodgman
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Enthusiast Service, Restoration & Tuning.
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