2009 R56 S. Towed home due to engine stopping on apparent electrical failure. Charged battery, started engine, tested alternator with showed 11.8 volt while running.
Replaced alternator (new not rebuilt) and battery due to no charging of battery, now it just cranks but no starting. Checked plugs and coils, they fire fine. Tried starting fluid with zero effect.
Ran cold compression test and the numbers are very odd. Dry-wet is #1 70 / 105 psi, #2 35/40, #3 35/42, #4 135/80 . Notice that #4 has wet cold compression test less than dry,
which is very odd. I did 3-4 compression tests on each cylinder, and used marine fogging oil for wet test. Timing chain tensioner replaced under warranty at 45k miles based on service bulletin and increased timing chain noise.
The car ran fine just before alternator replacement, so I do not know what to make of the compression numbers: I have done lots of compression tests in the past.

I feel this is something fuel related causing no start, and if the timing chain had gone then I would have some or all cylinders with zero compression, but the minimum is 30 psi.
Plugs looked ok, very faint hint of fuel on plug but not much. I am stumped. Is there something that would kill fuel supply ? All engine codes reset with Bluedriver.

 

Have you taken off valve cover to inspect chain & cams? Considered the possibility that carbon is holding the intake valves open? What were the codes you cleared?
Maybe you have more than one issue going on.

 

I have not yet removed the valve cover, but I guess that is my next option. The vast majority of the codes could be traced back to under voltage, but I also got a P15E8 pending, which is unusual and I consider it to be not important.