Failure to start falls into two categories:
The engine will not turn over – the starter motor will not run
The engine turns over but will not fire and run.
This article will address the second cause. If you engine will not turn over, see my other article.
The Jeep Cherokee like other vehicles needs two things to run: Fuel and ignition.
Fuel delivery can be easily checked with the use of a fuel pressure tester connected to the test port on the injector rail. In the event of an emergency, you can sacrifice a tire pressure gauge to test for proper fuel pressure. The correct pressure will be around 35 to 40 lbs depending on the vacuum state of the engine.
If you suspect a fuel delivery problem, first listen for the fuel pump to run. On most XJ Cherokees the pump will run a couple of seconds and then stop when the key is first switched to the on position. If the pump does not run, check the wiring to the fuel pump. Start to see if the proper voltage is present at the ballast resister located on the left front fender. You can also remove the fuel pump relay and use a jumper wire to energize the fuel pump.
If the fuel pump runs but does not produce the correct fuel pressure, check for leaks in the fuel limes. There is a rubber line inside the fuel tank that if it breaks will allow the system to loose pressure without any visible leaks. This one can be a real head scratchier to find.
If you have the proper fuel pressure and still the engine will not fire, check the ignition source. The ECU relations on two signals to determine the spark timing. The Crankshaft position sensor and the camshaft position sensor. The Crankshaft position sensor is located on the bell housing on the left side of the engine. There is a wiring connector on the manifold that sometimes corrodes. Check for a good connection at this point. Also, check the wires leading to the sensor as I have seen them damaged.
The camshaft sensor is located inside the distributor housing. The most common problem with this sensor is the wiring again the connector to the wiring harness. Also note that there are several ground wires that connect to the back of the engine block near the distributor. If these grounds wires are loose, the ECU can malfunction. Check these while checking the camshaft position sensor wiring.
If the distributor has been removed for any reason, verify the indexing of the distributor. If the distributor is even slightly off, the computer will not allow the engine to fire as a safety precaution. See my other article on distributor indexing.
Another part that can stop the flow of power to the ignition is the rotor in the distributor. Remove the distributor cap and verify that the contacts of the rotor are making contact with the cap and the tip is not excessively burned.