Exchanged coil, injector and spark plug with another cylinder, but problem persists. P0306 shows when car is accelerated hard and RPMs climb to 3-4k RPM. At this time CEL is on and you can feel that the engine is indeed misfiring.
Problem goes away when engine is turned off and immediately back on.
When the engine is back on, the Check Engine Light is off. When OBD codes are read, it looks like a command to erase all codes have been sent because IM Monitors are incomplete. Engine purrs perfectly. If driven at less than 2500 RPM for 50-100 miles, eventually, all IM Monitors complete successfully. If accelerated hard, the problem begins again.
Hey. A P0306 is a misfire code cilinder 6. Change the plug for nr 1 and drive again. When it stays on 6, your ignition coil is bad ,or injector 6 is the problem. So change ignition coil 6 to for example 4 and drive again. If it stays on P0306 its the injector. (This is for a N52) Regards Nico.
Nico:
Moved coil, spark plug and injector from cylinder 1 to 6 and it still shows P0306 when accelerated hard.
I had the same type symptoms happening for me, then one day, it started the misfiring and never cleared up.
1. I started by changing all plugs out, no change.
2. I moved the coilpacks around to see if I could at least get the misfire to move to the other bank, no change.
3. Then, I monitored engine data while running in driveway; it was not driveable at this point. Seemed to have low fuel pressure (this is an N54), so I changed the HPFP, no change.
4. When it would run, I could smell gas fumes pretty strong from the exhaust. At this point, I bit the bullet and replaced all 6 injectors (also used INPA s/w to code the new injectors in and reset all the faults that had been stored). Aaaannnnddd, thankfully that solved it. I had three clogged injectors.
Good luck. And when you source your injectors, look at the ones sold through AutoZone. They look like they came out of the same plant my OEMs came from. Right down to the laser etched BMW roundel and all that info that is stamped right there on the injector itself. This was about 50k miles ago.
rydeyz:
I replaced the injector in cylinder 6 but under high acceleration, it still fails with code P0306. This car has an N51 engine, so it is fairly easy to replace the injectors. But I don't think that is the source of the problem, otherwise, the problem would have gone away with the introduction of a new injector.
There is a possibility of low fuel pressure, intermittent connection to the coil or injector or that the cylinder itself is low on compression.
Thoughts?
I think I found the problem. The spark plugs that I bought for this car had the gap set too wide: 0.066 inches.
When I adjusted them to 0.044 inches, the problem went away.
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