I have R350 with later M272 (improved harmonic balancer) with 150K on it. It runs flawless, almost, except one recent mystery hiccup:

Occasionally, usually on colder morning, it misfire, whole left bank. Rough and shaky as expected. If running for 10-15 minutes - it recovers. And here is the mystery: If turned off after maybe 10 seconds after initial cold start and restarted immediately: right away it runs smooth, not a single skip.

If I let it run for a few minutes then It sets only generic misfire codes: P300, P304, P305, P306. Nothing else. Nothing in MB specific diagnostic either. EC light usually blinking then constant on.
If EC was reset earlier and I do not let it run for more than 10 seconds before restarting it - EC light will not be set and I can go whole day like nothing happened.

I am trying to deduct what it cannot be:
-it is not a camshaft sensors as they would be reported as MB specific camshaft sensor codes.
-It is not a knock sensor, same as above it would have own code.
-not anything else shared between left and right bank.
- not an injectors: would not fail whole side and then immediately cleared if restarted. Also tried to run half tank of Mobil Super (supposedly strongest detergent?). By the way, I only use Super, though various brands.
-not an ignition: got new platinum set about 10K ago. Also had to replace one coil (in that left bank), but that was obvious and no other problems with ignition since. Ignition also would not fail whole bank then cleared even if cold, I would think.
-I may imagine thing, but It appear to me that I can hear extra clicking when misfiring, like intake/exhaust valves with extra gap. But, after immediate restart that clicking is gone. If it really would be the valves, then I would think clicking would persist longer. Can injectors or something else be so audible when malfunctioning? Though, I am not 100% sure about it.
-Chain and/or tensioner: Takes 10 seconds to tension, but then why it would not recover on its own and require restart?

It would be easier if problem would be persistent. But it happened only on some days, and now I know to restart immediately.

There is hardly a good way to troubleshoot it without being able to replicate that problem reliably.

I guess I can wait till problem become more severe/ permanent, but posting here in hopes that someone may recognize that as something known. Any help with recognizing this problem is greatly appreciated.

Cheers Y'all!

This is an interesting enigma: Bk2 misfires on cue.

I think you're dealing with a combination of issues.

Can you go ahead with these troubleshooting steps:

• read long term fuel trims at hot idle
• read fuel rail pressure at various Rpm's
• move your single new coil to No3 Cyl

Report data.

Fuel pressure on that side which means maybe a leaky injector over night... and after you have key on the fuel pump refills line and gets pressure back up.

That is where I would start - when I ever I see misfire but no code other than misfire it tends to be Fuel or Air leak.

Just read codes again: Today reported misfire on 3 and 4, not on 5 and 6. THough in MB diagnostics all 4 misfire are recorded. So this is not just the left bank!
One more generic code P0000 which is "undefined".
With MB diagnostics: sensors are within range, as much as I can see. (Cannot read fuel pressure, no such thing in ECU and no talking to FSCU - see below).
Camshaft sensors adaptation all matching within 2 degrees. One of right sensors has max value of 2.75 degrees, Left: 1.25 and 2 degrees. IMHO this is tight.

Trying to read Fuel Pump Control Unit (FSCU). Got message: "..cannot communicate with FSCU, Check if your engine is equipped with it." I have '08 R350, Long, with M272. Does it have FSCU or fuel system on my car controlled by ECU?

If I supposed to be able to talk to FSCU and I cant, then I guess I will start unwinding that thread of troubleshooting.

Leaky to the point where it misfire - I would smell it I guess? I smell nothing unusual.
Clogged maybe? But it works fine if restarted immediately.
It might be fuel related as I cannot communicate to FSCU, see my other posts above.

"LTFT are cycling in range...."

FYI: they should be nearly fixed (never mind short terms). Were interested about long term only.

Lean or rich: what numbers for each bank?


You may want to get the firing order for your engine to see where your new ignition COP is setting cylinder timing.

The GDI ECU has the fuel rail pressure data.

Sounds like leaking injector or injectors or spark plugs to me maybe. When is the last time it was tuned up and got new plugs.

I say injector or injectors cuz they could leak overnight and you would be extremely rich on the first start off the day. And that blinking check engine light will cause the front catalyst on that side to plug up fairly easy and that will cost allot to replace. So maybe only let it run a few seconds at a time for I dunno say the first 6 starts off the day to try and keep the blinking light to a minimum until you find the problem.

You would have to ask Google or AI how to test the injectors as I'm not gonna type that out it's too long. When my car had issues and I exhausted all the electrical system I just replaced all 6 injectors with some from rock Auto and it fixed my misfires.

Good luck