2000 Jeep Cherokee Cranks but will not start
 

Start with using either a code reader or a scan tool to see if there are any codes or pending codes within the computer. If there are any, post the exact codes here (not a description) for comment.

In the absence of any codes, you need to determine whether you are missing either spark, fuel or fuel injector pulse.

Spark is a little tougher to test with the coil rail of the 00-01 XJ, so start with fuel. Try introducing a little bit of gas into the intake. If the engine starts and runs doing this, you have identified a "fuel delivery" problem. You need approximately 49 psi for the engine to fire and run. If the engine doesn't fire with this technique, then you need to test for both fuel injector pulse and spark.

You can use an inline "noid light" that you can purchase at your local parts store for testing fuel injector pulse, and you can test for spark using the procedure below.

Don't throw parts at this on a hunch. Use a testing based strategy to narrow down root cause. Good luck and let us know what you find!
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The coil design for the 00-01 is significantly different than that of the single coil and distributor setup on the earlier 4.0. You basically have three coils firing 6 plugs in the correct sequence, every crankshaft rotation (waste spark design). This is an engineering departure from the older, single spark every other crankshaft rotation.

You can test the coil pack like you would the old single coil design, but its more technically involved than physically accessing the spark plug end. Because of the design of the coil rail, don’t test the coil rail one spark plug port at a time. Testing one port at a time causes the remaining coil ports to be free floating (ie, not properly grounded through the spark plug). Free floating an encapsulated coil secondary causes significant increases in the voltage induced in the secondary. This increased voltage can easily exceed the dielectric breakdown of the coil secondary and could cause the coil windings to arc internally and break down the insulation. If this happens, it has the effect of reducing coil energy delivery potential in the best cases and in the worst cases, causes the coil to fail. You need to install all 6 spark plugs to ensure you won’t damage the coil rail.

Because it is difficult to guarantee that you can correctly ground all 6 plugs at once, you should make up 6 separate jumper wires about 2 feet long. Pull the rail and flip it upside down. Insert 6 sparkplugs into the rail. Attach one end of a jumper wire to the threaded part of the sparkplug with a large mouth alligator clip and attach the other end of the jumper wire to engine ground. Once all 6 are hooked up this way, you can then perform your engine cranking test while observing spark on all 6 plugs. You are looking for a strong, BLUE, snapping spark. Yellow/orange/white indicates a weak spark.

Proceed with the testing of fuel delivery, fuel injector pulse and spark (including the quality of the spark)

Gotta narrow it down to what you are "missing".

You could but I would personally push a little fuel into the intake to see if it fires. That is the best bang for your buck right now. Just because fuel comes out when you push the schrader valve, that doesn't mean that you have the correct amount of fuel pressure. A fuel pressure gauge (rent one inexpensively from local parts store; call around for availability) will tell you that. Approximately 49 psi for your vintage is required for fire. Much less and it won't pop. I'd be ruling out fuel first, then spark, then fuel injector pulse. In that order.

tjwalker gave you spot-on advice. Yes it would be a bad idea to throw parts at it, unless you like wasting money and spending time working in the freezing cold dark. Imagine how crappy it will feel to put coils and plugs in it, and have it still not start. Is it the new coils? is it the new plugs? or is it the original problem? Hmmm. You'll eventually end up back at square-1 rereading tjwalkers advice. At least start by testing fuel delivery by introducing fuel at the throttle body as suggested (look it up on youtube if curious). It only takes a moment to do this test.

Also, the opposite of the crappy feeling of throwing parts and not fixing the problem, is the great feeling of diagnosing the actual problem and fixing it on the first try. Makes you feel like the master of the universe (at least for a day or two).