First thing I'd do is hook up a scan tool capable of live data and look at the long term fuel trim.
I'm not clear on which parts of the 2000 engine were reused on the '95. Was the 2000 engine an OHV or SOHC ? I assume the 2000 was a 4.0L?
Using the 2000 PCM, you need 60PSI fuel pressure, doesn't matter than the 95 engine at the time used 35PSI. The fuel rail and possibly injectors are different so the 2000's rail and injectors would be swapped onto the '95 engine. However, you should have 60PSI since the pressure regulator is in the tank.
You wrote "I took a return line off of a 94explorer and hooked it up so as to not drownd the older motor". What exactly do you mean, that you used the old '95's fuel rail with its 35PSI (actually I think it's closer to 40PSI spec'd but 35PSI is like a threshold value of acceptability) return and piped the return back to the tank? If so, that you cannot do, it needs 60PSI. If you no longer have the 2000's fuel rail to switch it over, then I'd get one from a junkyard, from a '99 through '01 Explorer 4.0L.
All of the above is only my best guess. I'm not clear on which parts were transferred over to the replacement engine, but I am sure the '00 PCM operates on the assumption there is 60PSI fuel pressure.
I'm not clear on which parts of the 2000 engine were reused on the '95. Was the 2000 engine an OHV or SOHC ? I assume the 2000 was a 4.0L?
Using the 2000 PCM, you need 60PSI fuel pressure, doesn't matter than the 95 engine at the time used 35PSI. The fuel rail and possibly injectors are different so the 2000's rail and injectors would be swapped onto the '95 engine. However, you should have 60PSI since the pressure regulator is in the tank.
You wrote "I took a return line off of a 94explorer and hooked it up so as to not drownd the older motor". What exactly do you mean, that you used the old '95's fuel rail with its 35PSI (actually I think it's closer to 40PSI spec'd but 35PSI is like a threshold value of acceptability) return and piped the return back to the tank? If so, that you cannot do, it needs 60PSI. If you no longer have the 2000's fuel rail to switch it over, then I'd get one from a junkyard, from a '99 through '01 Explorer 4.0L.
All of the above is only my best guess. I'm not clear on which parts were transferred over to the replacement engine, but I am sure the '00 PCM operates on the assumption there is 60PSI fuel pressure.