M60 engine trouble :(

[winfred]

bad coil/plug/water/oil in the plug valley can do that too

Trajan, 1213 doesn't mean its too rich, it means the dme has detected excessive variation in the air fuel mixture, beyond what the o2 sensor can measure for a period of greater than 10 seconds.... It can be either rich or lean.
Since its only on one bank ,Cylinders 1-4, i would look at possible vacum leaks on that bank or see if the wiring harness going to the o2 sensor for that bank got damaged somehow. You didn't run over anything?
Since its one bank possible causes can be a stuck injector, low fuel pressure, airflow sensor problem etc.

[Traian]

The fuel consumption went sky high too. Before the CEL came on and she started limping, the first thing I noticed was that it was using a lot more gas that usual at steady hwy speed.

There is a test in the Bentley for the fuel pressure regulator, I will try that tomorrow.

I'll try a battery restet too, the battery ran down one night a couple of weeks ago when i forgot the dome light on, and after i charged it up the car ran better than before haha Guessing it's not the crank sensor as the car starts fine, not sure. It starts better after i leave it off for a few min.

The valve cover gasket is leaking a bit, some of the plugs are pretty oily. Should I test the coils somehow too?

One of the O2 sensors was changed at the dealer 50k km ago, the other one I don't know. I wonder why they didn't change both...