Well it can be several things. Two of the most common things are: no spark from the coil & low or no fuel pressure. To check for spark at the plugs. You have to pull the one of the plug wires and hold it ½” away from the engine block which is ground. You may want to use insulated pliers to hold the wire if the wires are old, to avoid being zapped. This is best observed at night. If you do not get arcing while cranking the engine then I would check the Crank & Cam shaft sensors. Also the cap and rotor might be frigged and maybe the coil is bad. You have to keep working backwards until you find juice. A Haynes manual is necessary for testing the sensors.
If you do see spark, then I assume it’s the fuel pump or a clogged gas filter. The pump is located inside of the gas tank. You can measure the fuel pressure at the fuel rail. It should be around 30 to 40 psig. Simply pushing the fuel rail valve, to check for pressure, may not be good enough, but if nothing squirts out then you now know.
Another scenario is that the PCM is not grounding the ADS relay, which powers the fuel pump relay.
94 Black Laredo 4-Liter with QuadraTrac (42RE trans & NP249 TC) 200,000 + miles purchased new
88 Cherokee 2-door with 5speed manual 139K miles(deceased) purchased new