my taurus FFV motor does not have a fuel pressure regulator. it does have a fuel pressure sensor though. and a fuel blend sensor. the blend sensor is $450. my rich running issue went away when i started using a higher ethanol concentration. i slowly am going back to a E10 mix and my CEL has not come on yet. dont know why my issue went away with E50+ fuel mix.
Could the higher ethanol cleaned the injectors?
That would be my suspicion.
Perhaps the blend sensor system is failing, i.e., losing the ability to accurately measure the blend, so your car mistakenly “thinks” you have high EtOH and sets the injectors accordingly. Running 50+% EtOH makes it all OK.