Chrysler Repair: 90 lebaron convertible, lebaron convertible, oxygen sensor

Question
have replaced asd relay and fuel pump and power control module and this car still loses fuel pressure, also fuel reg was replaced. each time something else is done car runs good for a few minutes and then returns to running bad again, no fp ?help.

Answer
Have you checked for fault codes? "On-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then watch the check engine light to begin to flash, pause, flash, etc. Count the number of flashes before each pause. Then repeat. Then combine the numbers in pairs in order they appeared to form two-digit fault codes. You can get a decoder at www.allpar.com/fix/codes.html
Write back for detailed suggestions based on the codes. Is there power to the pump when the engine runs bad, or is it the pressure that drops? Also tell me the engine you are have in the car.
You may need to have a Chrysler shop with DRB II analyzer observe the parameters dynamically to detect what is changing. Could it be an egr valve that is sticking open? Maybe something specific to the time of occurence is that the controller switches into fully controlled mode after a few minutes from a pre-programmed warm up setting at that time. Perhaps the code will show an issue with the oxygen sensor.
I'll be interested to know what you learn.
Roland