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Hello everyone! Please help.. 2011 mini R56 non turbo fresh rebuild, engine miss cylinder 2&3. first start up engine missed for 10 seconds then engine idled up then settled ran great until i turned it off and restarted it miss on 2&3.
moved coils around same moved plugs around same ran spark tester between coil and plugs all good did compression test all cylinders 215+ PSI checked fuel pressure 50 PSI bought 2 new injectors replaced 2&3 same result constant miss unplugged injectors on 2&3 used Noid light to test DME pulse signal, good Signal. i am out of things to check anyone else have any ideas?, it shouldn’t be missing on 2&3 but it is..
Disconnect the inlet camshaft position sensor connector. Does the misfire stop? If it does, you have loose or fallen valve seats.
I've just went through all of this on my '09 project car. I got the car cheap, and found one of the #1 intake valve seats was broken and it had fallen. Two of the exhaust seats on cylinder 4 had fallen. I took the head to a local machine shop, and they replace the defective seats and staked all of the others. 10 miles later, the #4 cylinder dropped again. So the head went back to the shop. They replaced both exhaust valve seats in cylinder 4 again. Everything was fine for a while, and the engine ran well. Then it developed a hot idle (only) misfire on cylinder 2. Compression was good, and leak down on cylinder 2 was 9%. But, it would still misfire when the engine was at operating temp but only at idle. If I disconnected the intake camshaft sensor while the engine was misfiring at idle (taking the engine out of the valvetronic mode), the misfire would disappear. At the 4000 mile mark, it started misfiring on cylinders 3 & 4. No compression on cylinders 3 & 4. Here's what I found when I pulled the head.
Cyl 2
Cyl 3
Cyl 4
Now, why did I have a hot idle misfire on cylinder 2 before the #3 & #4 cylinder valve seats failed?
What I learned is this (special thanks to the MINI2 forum): The DME controls engine idle on these engines by altering the intake valve, but it only uses one valve (the one closest to the front of the engine). The second intake valve doesn't start to open until the eccentric shaft reaches approximately 150 degrees; this gives your more fuel and air at max power. The typical eccentric shaft position ranges from 18 to 35 degrees at idle depending on engine temperature and other factors. When you disconnect the intake camshaft position sensor, the DME detects the fault, and goes to a secondary idle control strategy using the throttle body to control the amount of air entering the engine. This drives the eccentric shaft to 171 degrees (full valve lift), so both intake valves are opening. My misfire was gone, but this didn't fix the loose valve seat.
If you look at my first picture (cyl 2), you may notice that the intake valve seat that dropped is the one toward the front. Since that intake valve barely opens at idle (I've heard on the forum 180 microns ... that ain't much), if that valve seats drops even a little, you won't have any air or fuel entering the cylinder ... MISFIRE! To make this even more fun, the seat was loose and it would fall when the engine reached operating temperature due how the aluminum from the cylinder head expands at a different rate compared to the steel valve seat. Off idle the engine ran fine because the eccentric shaft opens the valves more.
Finally, the #3 cylinder valve seat broke and dropped ... massive misfire. Cylinder 4 also dropped an intake seat, and I pulled they cylinder head again.
So, the head when back to my local machine shop, but they didn't have a cutter small enough to cut such a small valve seat, so they sent the head to a partner shop (Allied Cylinder head) in GA. We're replacing all the valve seats this time with the deeper ones.
OBTW, Factory valve seats are only .22 or .23 deep (intake/exhaust). The replacement seats are .30 or more, so I'll have more press-fit to hold them in place. Hopefully ... 3d time's the charm!
Lastly, compression check and leak-down check numbers can fool you if you have a loose valve seat. Valve seats tend to drop after the head goes to the machine shop for a valve job. What I suspect is the machining process to grind the valve seat causes a twisting motion on the seat and disturbs the press-fit between the seat and the cylinder head; this loosens the seat and makes it more susceptible to dropping out when the engine gets hot. You said your engine is a fresh rebuild, so I'll bet you have valve seat issues.
