About 1/4 of the time, when I start up my 2009 MCS in the morning or after a full day at work, the engine will be incredibly grumpy and try its best to die. And just about every 25-30 days, I'll get a check engine light about misfires. Thing is, after a few moments of stumbling, all is well. And again, it's only problematic about 1/4 of the time; more often than not, it starts up just fine.

This morning, I caught a rather extreme example on video (it's not usually quite this bad).
www.youtube.com/watch?v=OTNISjVU8d4
Note: Usually when it stumbles, I'll give it some gas to try and keep it alive. That works fairly well, but in this video I made a point of not touching any pedals at all. Also, I had the windows down and there was a fairly strong odor of gasoline in the garage at the end of all this drama.

This rough start business has been going on for a while and at first I was convinced it was due to excessive carbon buildup. So, about a month ago I had that walnut blasting service done to clean out the intake ports. That didn't seem to affect this issue much; 3-4 days after the walnuts it complained again when I went out in the morning (again, doesn't happen all the time).

I've read people describe similar behavior in here before, some pointing to HPFP issues, a few point to timing chain issues, and so on. Seems pretty hard to nail down a specific culprit based on description alone. So, maybe this video will help... anyone seen this issue before and/or know what it is?

 

I'm having similar issues as well with my 2008 MCS. Hopeful someone has a cure. I did a seafoam treatment last night, but still had a bit of stumbling this morning, though it only lasted for about 5-10 seconds.

https://www.northamericanmotoring.co...old-start.html

 

That might be an ignition issue of some kind. Have you checked the plugs and coils?

 

My bet is on HPFP...

I'm surprised its not throwing any codes running like that...

Typical R56. They throw codes for everything, but then when its actually running like crap and you need a code it won't throw one.

 

Check engine light is on, I just haven't had time to put the Bavarian Technic on it yet. All the other times it was for misfires in multiple cylinders (pretty sure it counts misfires and doesn't light the CEL until there are "enough").

When I had the walnut cleaning done, part of that service was to update the ECU as well. The technician said they made it less sensitive to reported misfire faults.

 

I saw some video on YouTube of a guy who had a similar problem that was fixed with HPFP replacement. But hitting the accelerator on his did very little, as the throttle was already wide open trying to compensate. On mine, throttle still revs the engine out of the sputtering/choking zone. HPFP is still a candidate in my mind, but I have my doubts, too.

 

09 S, around 7k miles in dec 2010 when mine started showing similar symptoms. Check engine light disappears after a few restarts later, dealer can't duplicate it so I'm sent home twice.

1 month & a few hundred miles later, check engine light stays on (limp mode). Service performed says HPFP failure... found fault code 2880... per SIB 010410, replaced HPFP.

Never had the same problem again, 5k miles & 1+ yr later

 

Finally took a look at the ECU and all that was reported in there were misfires on all cylinders. Nothing really to indicate the cause of the misfires.

 

Got the car back from the dealership this past weekend, and it's been running fine ever since. HPFP it was, it seems.

They said they couldn't get it to throw any HPFP-related codes, but that the pressure reading was a bit low, so that's what they thought it was and they replaced it under that extended warranty.

 

Mine is very similar to this, misfires in the morning but after giving it some gas, it runs fine the rest of the day. Let it cool down and it misfires again. It's been a the dealer for 3 weeks. 38k miles

Services performed...
Walnut blast
New Timing chain, guides and tensioner
New HPFP
Walnut Blast AGAIN
Injector cleaning
Fuel system flush
Dropped the gas tank to rule out contaminants

It is STILL misfiring.

The dealer has been VERY good and will NOT let me have the car back until they are sure that the problem is resolved.

Frustrating, but hopefully it gets fixed.

 

Ouch!
The HPFP replacement has been rock solid for me so far.

 

30+ days in the shop and still misfiring!

They have now done this in addition to the below...
Compression check (good)
Leak down test (good)
replaced the fuel injectors
Fuel pressure check high and low (good)

Still misfiring!!!!

They are now replacing the Valve Lifters