PFP1971

Hello to all! I found much needed info here in the past but this one’s got me stumped and could use some help.
2006 R350 cylinder #2 misfire. Was running perfect, stopped for gas, restarted and was running rough and check engine light came on. Turned off n restarted and ran/drove fine for 15 min till I got home n started missing again. Shut off n restarted and ran fine. Done this several times until it no longer worked. Pulled code p0302 so swapped coils, no change. Swapped plugs no change. Assumed it was injector so new injector, ran great for 5 minutes then back to square one. I even swapped injectors around just in case. Definitely have power to injector, checked all wiring, o2 sensors, cats, coils, cam sensors, plugs. I have erased code p0302 after every parts swap/change and upon startup it runs fine for a minute then very slight idle drop and back up then check engine light starts flashing then stays on n code sets. Sometimes even with this code present engine revs smooth, other times I can feel mis.
I know my way around a cars pretty good so not a newbie but this has got me stumped and at total loss.
Garaged since new, I’m second owner and garaged w/130,000 highway. Last year complete MB intake, p/s pump, a/c clutch, both batteries.
Any ideas would be VERY MUCH appreciated BESIDES taking it to dealership.
Thank you, Paul.

Sveina

Something wrong with the gas you filled? If so I would have guessed that it would not always be cylinder two. Compression check? Leakdown test? Got a oscilloscope to check signal to coil and signal to injector? Did the cylinder two spark plug look any different than the others? Got access to a broad band lambda to insert in tail pipe?

PFP1971

Hello svenia, gas was my first thought but only affects #2 cyl. I did not test compression or perform leak down as of yet and don’t have a lambda. All plugs look identical, clean n like new. I did however erase code p0302 again today and this time disconnected MAF sensor and car ran good so I removed maf and cleaned with maf cleaner, reinstalled and added 4 gallons of 91 octane, ran ok for a few minutes then back to the issue b4. Erased code and disconnected maf again and ran fine although at 750 rpm I still feel slight mis but this probably has to do with ALL cylinders now since maf was disconnected. It ran so smooth at 775+ rpm you can’t even tell it’s running with exception of engine noise. I let it run a bit without maf connected to get new fuel thru injectors but don’t know what damage might be done from running without maf connected like fuel dumping into cats. Funny thing is with maf disconnected and running I get no check engine light, once plugged in idle goes down a hair then back up then light sets and I get code p0302. I did this several (5-6) times. Definitely leaning towards maf now but I’m not one to throw parts at a car just because. Baffled why maf only effects cyl #2 on this Benz and worried about spending $$$ on a new maf and not fixing problem. But nonetheless I think I’m on to something with this maf.

chassis

On an old high mileage car like this I would start throwing parts at it.

spark plugs, doesn’t matter if they look good
coils and boots
cam position sensors all 4
cam magnets all 4
crank position sensor
mass airflow sensor
coolant temp sensor
oxygen sensors all 4

If the above doesn’t help do a compression test. Probably a good idea to check compression when replacing the plugs, coils and boots.

Sveina

MAF is a good place to start.

Checked the wiring and connections for the engine ground cable?

lkchris

A misfire points to more than just ignition system.

Misfire can occur because the mixture cannot be ignited. This suggests, vacuum leak, defective MAF, etc.

bicylindrico

An SDS system can perform a compression test to rule out any mechanical issues. MAF will NEVER make one cylinder consistently fail.