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Cylinder 2 Misfire

8K views 3 replies 2 participants last post by  JKraft 
#1 ·
Hello, all. Brand new to the forum. Just got an 07 R56, N12 with 97k on the clock. Driving it home I noticed, after a few miles of driving, that it was idling very rough when almost stopped and stopped. There was also a bit of lag when getting on the gas from a stop and a slight loping when cruising. I get her hooked up to my diagnostic tool and pull a P2414 and P0302.
I changed out the upstream o2 sensor and, starting it up, the engine would rev up to 2500 for a few seconds, then bounce between 1500-2500. Put it in gear, then back in park and it was idling rock solid. Took it for a test drive and the rough idle came back when I got back home (P0302 again), with the exhaust smelling rich.
Pulled the plug and noticed some carbon fouling on the base of the insulator and on top of the piston. I changed out the coil pack and it did the same warmup as before. I noticed less stumbling on acceleration and slightly less loping at constant speed. Get back home and wham, rough idle and P0302 again but with proper smelling exhaust. I'm at a bit of a loss here and would like to get her on the road soon.
 
#2 ·
You mentioned that you changed the coil pack, did you also change the plugs and plug leads ? If you have a miss fire on any cylinder, your going to be pumping an incorrect exhaust so your o2 sensor will kick off. You may find the O2 sensor was fine and there are other issues upstream like bad plug/s, bad plug leads, vacuum leak on the intake manifold, faulty injector or poor injector signal from a damaged or incorrectly seated signal lead. Think old school as you may find it will help locate the fault and be aware generic fault readers can and will miss some BMW specific fault codes which wont help your diagnostics. I once had an Injector fault code on #2 and ran rough, costed out a set of injectors and the fault was a half clipped on injector lead ! Clipped it on correctly, cleared the fault, no more issues, never discount the old fashioned way of fault finding and remember codes are just a guide. :)
 
#3 ·
Update: After 3 weeks of scratching my head I bit the bullet and took the car to a mini specialist. They found good spark, good fuel delivery, excellent compression and and no leaks. Mechanically, the engine is in top shape but the misfire continues. The mechanic has a call in to Mini USA to try to get this figured out as they are stumped. A couple of thoughts: maybe bad ECU programming or a knock sensor malfunction?
 
#4 ·
Another update: Turns out the "specialist" was trying to scam me. After telling me the compression and leak down were fine he then says that I've lost compression in the #2 cylinder and the ONLY fix was to replace the engine... for $9K. I probed for more info and the guy kept changing his story about what was wrong so I took the green machine to a reputable shop and they discovered fouling on the intake valves (previous owner must've been using cheap gas and cheaper oil) and the timing chain was worn out. That being said, the rest of the engine is apparently running like new. Should be getting the car back today or tomorrow.
 
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