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I need some advice on how to proceed. Don't want to spend time playing parts roulette .The check engine light flashes upon startup and then stays on. Always starts easily. OBD 2says misfire on Cylinder 1,3 & 4. Code P0300, P0303,P0304 & P0110 (Intake air temperature Circuit), P0136 (O2 Circuit (Bank 1 sensor 2). Replaced Bosch double platinum with NGK on cylinders 1234 and still started but was still shaking so decided to replace all the plugs anyway. Switched ignition coil #5 (Bosch OEM) but not the wires to 1 but OBD code still said misfire on 1 making me believe it's not the ignition coil. Bought aftermarket wires and tried it on Cylinder #1 but still showing a misfire when I checked the OBD2 scanner. Replaced all ignition wires.Things I have done (or have yet to) so far:

• Check fuse to ignition coil (All good)
• Check for any cracked broken vacuum lines
• Check fire harness for any cracks (nothing out of the ordinary)
• Clean the MAF and test drive (removed the plug while it was running and the car died instantly, not sure what that means. MAF is the OEM Bosch type
• Check the EGR pipe - may need cleaning or replacement
• Check cats. Simple test before and after using a temp gun.
• Use an Endoscope to look at the cylinders 1,3 & 4
• Do a compression test ( Came back low on 4 - 120 PSI )
• Check/Replace fuel filter? Check fuel pressure
• Fuel Filter (although wouldn't this show a DTC code?)

Anything else?The ML was parked and it stored outside in the elements in Portland, OR since mid 2022. I then replaced the battery and had it towed to California. Has 176,534 miles I put new gas before I started it.

I am tempted to remove the secondary cat, but I live in California.

What is the best scan tool for this model year Benz? I Also have a 2007 c230 and a T1N so it would be nice to get a scan tool that is compatible. The Innova 5610 that I have just reads errors codes but does not give me live data.

What are the proper Compression numbers?

Sorry for all the questions and thanks in advance.

S550Joe

I can't answer all of your questions, I drive a 2018 S560 4Matic, my check engine light came on, I took it to the dealership and learned that I have a faulty #5 ignition coil that has a warranty extension for this part. You may want to check if yours is covered by the extended warranty.