I replaced PCV system as it was clogged and since then the car does not run all the time. At first it was fine and I was able to drive it with better performance. Shut it off in driveway and cannot get it to run. Stalls, misses, black smoke out tailpipe. Replaced plugs and all coils today and it ran great but then the problem returned. No codes although CEL lights up from time to time and flashes. Fuel pressure at rail is @ 50 psi. Any ideas?

It has 215K miles on it.

Sounds like your spark plugs are fouling. Black smoke is too much gasoline. You want to check for air leaks at the intake manifold, intercooler piping, injectors, and anything else that was removed.

A flashing CEL means that there is a multiple misfire.
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Keeping it running is better than buying new

One of my precepts of troubleshooting is - What just happened?

Check your work - something connected wrong, or not connected.

If you worked with multi-pin connectors, look inside them to see if a pin has backed in.

On our '88 745 GLE, one of the pins in the mass air sensor backed in, and the car would not accelerate. Interestingly, it went fast in reverse, but not going forward.

The car had just been tuned by a dealer tech, and in order to change the air cleaner, the MAS had to be unplugged.

If a check of your work does not produce results, do not throw parts at it - chances are only one thing is wrong - see a dealer or indy?