My 4.0 Cherokee Fuel Injected has been getting harder to start. I replaced the air filter and it made no difference. I went out this AM and it would not start.It would turn and turn but would not fire. What would cause this? Thanks Guys!

I would check your fuel pressure. Pump sounds like it's giving up. Cycle the key a few times and listen if the fuel pump is running.

Check your crank sensor

Like mentioned,do you heard the fuel pump? Also isnt the crank sensor located in the bellhousing on these?

how long have the plugs been in?

Try this: When you first get in, just turn the key to the on position without starting it and wait until you hear the fuel pump come on. Then turn the key off and on several times. Then try and start the Jeep. My Jeep had this problem and it wound up being 3 bad leaking capacitors in my computer. There are several how-to's on the internet on how to replace the bad caps inside the computer.

Just worked on a customer same year / engine Cherokee. Came in to replace the front diff assy and went to start after work was done- (had to tow in due to dead battery)- didn't want to start (cranked fine) LONG story short- held pedal to floor - finally started but took until it was warmed up to finally idle. Cleaned throttle body (filty black) Plugs were shot- never does maintenance. End of that story. Hope this helps- like other guys noted- very common for crank sensor to go. Check for spark!