Nissan Repair: 1991 pathfinder, ..heavy fuel odor out exhaust..runs lumpy, fuel pressure regulator, oxygen sensor

Question
I have a 1991 nissan pathfinder. It was running great and then it started to run lumpy, go through heavy fuel and lots of fuel odor out the exhaust. I got the fuel pump changed, changed fuel injectors, distributor, rotor, filters. and it still ran lumpy and with the same symptoms.

Then all of a sudden it ran good again for about a month, then it started having the same symptoms again. So i took off the fuel rail, check which plugs were wet, # 4 # 5 # 6 were visible wet, and the other 3 looked to have rich fuel indications on them . So i changed three injectors  and all the plugs, it ran fine for about 3 mins, and then the same symptoms all came back again.

So i used the ecu self dianogstics and no fault , but it did tell me on dianogstics #1 and #2 and rich indications...so i went to the manual and it suggest fuel injectors, fuel regulator, MAF sensor, and oxygen sensor.....so i have an oxygen sensor on order....am i on the right track? could it be somethign else? and i believe the o2 sensor is on the cat converter..is this so? and how diffucult is it to change. . if you can help me out this would be great assistance.  

Answer
Lawrence,

I had a 350Z do what you describe.  The fuel pump went and trash went through the fuel system taking out two injectors.  Then it did it again and the pressure regulator was defective.  So, flush the fuel line rail and check and or replace the fuel pressure regulator.  Be sure to change the fuel filter again as trash as probably partially blocked it.  This messes with the fuel pressure when the filter gets trashed.