Tricking The Ecm

I have little to no backpressure and my o2 sensor gets to lean a reading so it kicks the ecm(1993 CHEV - OBD1) into limp mode. My 5.7L gets about 7 mpg. I m trying to find out how to trick the ecm by sending the correct voltage from the o2 sensor to fix my problem rather than having to add backpressure. I know there are o2 simulators for sale but nothing for my model year. If you have any ideas on how to do this, I would certainly like to hear them.