I have a 2000 Jeep Cherokee Classic with the 4.0 liter. I have the check engline light that comes back as "system too lean bank 1". I have changed both O2 sensors, coil pack, crank sensor, and plugs. The next thing I plan to change is the MAP sensor. The gas mileage has gone from 17-20 MPG to 10-14 MPG and it runs rough. After changing the O2 sensors the MPG has gone to 13-15 MPG. ANy thoughts if I am going the right way? If MAP sensor does not fix it, I do not know what change next............

 

Did you reset teh ECU after oxygen sensor swap?
I would do that, drive it for 50 key cycles. After 50 key cycles if you still have the code, do MAP sensor, then check bank 1 injector spray pattern

 

Not sure if I cleared the ECU. I saw something on another thread that said to unhook the positive cable and hold it to the negative cable for 30 seconds then hook it back up and then turn ignition on then turn lights on then off and turn ignition off. Is that how you reset it? I havent made it to 50 cycles yet.... just having issues tracking this issue down.

 

21. Disconnect your battery terminals and hold them together for 30 seconds. After those 30 seconds, reattach the terminals to the battery.

22. Turn your ignition to the "ON" position - DO NOT START YOUR JEEP.

23. Turn your headlights on, wait 10 seconds, then turn them off.

24. Turn the ignition to the "OFF" position.

25. Start your Jeep. Your ECU is now reset and will "relearn" the proper fuel trim levels for the new injectors over the next 50 warm up cycles.