No it does not function that way. Unless you figure out how to make the sensors lie you cannot change the programming. Search the Nutter Bypass. This removes the computer and helps with power. I have done this and my engine wen from bogging down at 2800rpm to pulling all the way to redline.
Ok so can I tune the ecm so I get more horses or torque for better performance?
The link posted up by 89yjsahara258 is THE definitive online resource for getting to know the engine setup you have.
The ECM is crude at best, there is no way of retuning it that I know of. It is pre-OBD1/OBD2. There aren't even any aftermarket readers for the diagnostic ports (you have to make your own). The computer is programmed to keep the A/F mix as close to the 14.7:1 ratio as possible by bleeding-in/cutting-off air in using the stepper motor pins at the rear of the carb body. Disable the computer by doing the Nutter Bypass and you could retune the carb for better power, but you might not pass emissions and stay street legal.
Here in CA, our street legal options for the 1990 4.2L YJ are:
Sticking with the Carter BBD. Its a decent carb, but it takes alot of work and polishing to keep it running well. You cannot swap in any other carb.
Upgrading to the California Howell TBI kit. Pricey, but from my experience with it so far, its worth it.
Upgrading to Mopar MPFI kit. Expensive. Really expensive.
Engine swap to something fuel injected like the Jeep 4.0L
The Howell and the Mopar kits are C.A.R.B. approved kits.
You might be able to get better performance by putting in an MSD ignition module.
The Team Rush upgrade is something that I think every 4.2L should have done to it.
If you replaced the carb, or whoever did, it lost most if not all the crap lol. Add a ground, do the team rush, you will need to leave stuff in even if its not working to pass emissions out there. I got a 90, replaced the carb as you did, if your ignition box gives trouble think of upgrading.