Intermittent misfire. Can't pinpoint cause 2010 r56
 

Over the last few months I have been occasionally experiencing a misfire. Not noticeable at startup, no long/hard starting, not low on compression, valves cleaned, spark plugs replaced and gapped properly. It happened today while going down the highway at 65, but didnt happen at all yesterday when i drove 225 miles to minneapolis and back on the interstate. A month ago it happened after driving 200 miles to milwaukee. The spark plugs looked a little fouled, and the gaps were a bit larger than they should have been. Most likely from the last time I had it at the dealer. I replaced the spark plugs with oem plugs, made sure all were tapped properly. I had no issues since that point....until today. I'm drawing a blank as to what it could be. I'm not getting any code pointing me to the hpfp, and checked compression which also left me stumped. The only codes I have seen was misfire related, and had a momentary lean bank one a few weeks ago which resolved itself in a few miles. What I've experienced so far has been occasional sluggishness off the line (like it was getting too little or too much air) however it was only once every couple weeks, random misfire (felt like I had zero power and was completely audible, almost as if it were in momentary limp mode or out if fuel).....any info would be great. 102k, mostly stock, 1200mi on oil, 800mi on transmission oil, valves cleaned 5k ago.

check fuel pressure to the hpfp. theres no pressure sensor on the low side and could sometimes throw faults for a hpfp. other than that i would probably get the timing checked and chain tensioner replaced if the timing is spot on. check the vanos solenoids and actuators. i've come across a clubman once with random misfires but ran almost top notch and the intermediate lever was out of place. but if you've checked all of the above then what i said is another path you can follow.

my tensioners and chain were replaced at 59k, but I have not done anything with the vanos. The car only seems to missfire after long runs under steady throttle. Typically using cruise control. Once im in traffic after 200 or so miles in cruise it falls flat like the cam position is wrong. Now that you mention the vanos is somewhat fits. How do I diagnose that?

if you pull the valve cover and can try to turn the cam the vanos unit and cam should spin in tandem. if there's a few degrees of movement in the cam, your vanos unit is bad. after turning it, it'll set itself into position so it wont turn independent anymore. you usually change the unit and solenoid if that occurs. myself personally i have only 52k with no tensioner/chain issues. im still changing it as security so the chain doesn't skip. preventative maintenance.

I had mine replaced under warranty. There was a service bulletin for my car so it was at no cost. Was 3mm beyond max tolerance. I'm replacing the off/valve cover assembly on Thursday so I'll have to check the vanos assy at the same time. It seems too intermittent to be the hpfp, and I've found zero related codes this far. Thanks a bunch for the input.

A p2096 code finally showed it's face today. This paired with the sluggish behavior, slightly different exhaust smell, and hesitation im leaning towards a Clogged or partially clogged off system. Valve cover on the way, and while im at it vanos.

have you by any chance checked your exhaust? right around the flexpipe or welded areas? i've seen that mess with the O2 readings

Hi, did you fix your problem?

I have a very similar behavior on my '07 mini.
It'll start ok but after 15 minutes or so in traffic, or once I stop after being for a while on the highway the misfire comes up and the car shakes a lot.
Tried replacing spark plugs and coils, didn't help. I'm also getting a p2096 along with the misfire (P0301).

If it was fixed, what exactly was it? I had the valve cover replaced a while ago (there was a small leak). Is that what you were referring to? replacing the valve cover? did you replace the vanos solenoid too?

Thanks for the info.