1995 Jeep Cherokee Failed Only NO Part of Smog Test

Sounds like you've replaced the main components on your Jeep Cherokee necessary to control (lower) NOx. NO is created when engine combustion temperatures rise above 2500F. So anything you can do to keep the engine cool is going to help. With that said, running your Jeep extra hot before the smog test is not recommended. Running hot will help burn off HC and CO, but will increase NO. It's best to smog test (also the law) at normal operating temperature with all accessories turned off.

You're probably ready for your next smog check having replaced the main components responsible for proper fuel control; oxygen sensor, MAP, and ECT. If your Jeep still fails the smog check we recommend two things in particular, conduct a fuel feedback test to ensure your Jeep Cherokee's ECU is commanding the fuel injectors to properly when an increase or decrease in MAP frequency is detected. Assuming the MAP is functioning properly and the signals are reaching the ECU the ECU should command "rich or lean" with MAP frequency increases.

Same applies to the oxygen sensor only in reverse; with lower O2 voltage your Jeep's ECU should command more fuel delivery and visa versa. Assuming the new components are working we just want to make sure the new components are connected properly and their signals are reaching the ECU; and that the ECU is operating properly. Although your Cherokee apparently hasn't failed CO, it is important that CO is controlled. Your Jeep's CAT needs to run slightly rich in order to control and lower NO emissions. In regards to the CAT... your VIR mentioning the CAT as a "pass" simply indicates that the smog technician inspected the catalytic converter for proper fit and placement. This does not mean your Jeep Cherokee's catalytic converter is actually performing as required. There is still possibility of having a defective CAT and it causing high NOx failure by not reducing NOx effectively.