Hopefully there is a E53/M54 wizard out there that can assist me. Will list things out in point form so it's easier to follow progression of the problem.

1. 2002 E53, 444,000Km - engine was running perfectly, until I parked it for 10 days over the Thanksgiving break.

2. Tried to start after thanksgiving - no go - thought it was the starter or battery so replaced starter and batt was fine, but no start. This issue turned out to be no compression due apparently to hydraulic lifters losing pressure from sitting so long (?). Ended up getting it to start by just cranking it for like 90 secs till compression returned. It seemed to run fine after that.

3. Drove it for about 130 km - all good, until I got on freeway and accelerated up to speed - moments later it started running rough and I got a "misfire cyc 1 with fuel shutoff" error code.

4. Installed new plugs, swapped Cyc1 and Cyc2 coil packs to see if issue moved. Started fine but again under heavy load, misfire Cyc1 returns. Swapped out Cyc1 injector. Verified all elec connections to injectors are solid. No change, same thing on next test drive. The Cyc1 injector does indeed appear to shutoff when the issue occurs (cannot hear it firing/clicking via stethoscope/screwdriver), so maybe the ECU is shutting it down? Question is why.

5. Exhaust is fumy (been that way for a few years) largely because either downstream O2s are bad (not likely) or the aftermarket Cat is crap and probably failed after 6 mo (more likely). Not sure if the fumy exhaust could lead to current issue with misfire Cyc1, but aware of that issue and will look at new O2s once I slay this misfiring dragon.

6. Further background info - When I had the plenum off to change out the starter, I replaced the crankshaft sensor (put new one in since it was accessible with starter out), cleaned the injectors, CCV system is less than year old (inspected all hoses associated with it - all good), inspected/replaced any bad vac hoses, DISA, ISV, MAF, throttle body all in good working order.

Anyone have any ideas? Thanks in advance.