99 or 00 cherokee ran fine then suddenly no start.cranks fine.sprayed starting fluid in air housing and it fired,but no start.new fuel pump,no sound.new crank sensor-nothing.fp relay clicks

Check for spark.. pull one spark plug out set it on bare metal(away from cyl hole fuel could light from spark) turn vehicle over and look for spark should be a nice lightning bolt looking spark... blue spark is weak spark.. and see if it's getting spark...,, if not,,."try new plugs.,wires,distributor cap&rotor " also first.spray a little starting fluid down the injection system turn it over and see if it fires.if it does then it's a fuel issue prob not electrical... try that.hope it helps

Does it crank over If no, then try jumping it from another car.
If yes it cranks but doesn't fire up, try spraying a small squirt of starting fluid into the air intake. If it fires up then dies it is a fuel problem. Very likely low on fuel or fuel pump circuit.
If it cranks but doesn't start with starting fluid there is a problem in the ignition-spark system.

Okay, the possibilities are great. need to narrow it down a little.
If it fails to crank over it is likely the battery.
If it cranks over ok, but fails to start it is either lack of fuel or lack of spark.
the Quickest way to identify lack of fuel or lack of spark is to spray in a 2 second dose of starting fluid into the air intake. If it fires up then dies in this test it is lack of fuel most common suspect is fuel pump relay or fuel pump.
If it fails to fire up on the starting fluid test it is lack of spark. Electronic ignition trouble shoot procedure from your shop manual for your VIN number will be required.

Need four basics to start the engine; timing, spark, fuel and air.

Is the engine cranking? If so, have someone to spray 'starter fluid' into the immediate air induction port. If it doesn't fire and run for a few seconds, check the distributor source. If it does fire and run for a second or two, you may have a fuel pump down.

How many miles on the car? Have you checked the fuel pressure when it doesn't want to start? Do that first and then move on from there. To quickly test fuel pressure with no special equip get a can of starting fluid from the auto parts store, when it fails to start spray the fluid into the air intake of the engine well it is cranking, if it fires up then the fuel pump is likely not running on for some reason. This can be electrical in nature or just a failed electric fuel pump

If a starter is able to crank the engine but it won't start you usually have either an electrical or fuel problem. It's also remotely possibly that it's compression.If an engine has proper fuel, spark and compression, it will start when you crank it. So your challange is to find out which part isn't working right. Start with fuel. Spray a little starting fluid into the air intake while someone tries to start the engine. If it starts briefly when you're spraying starting fluid, you probably have a fuel delivery problem. That could be injectors, fuel pump, fuel filter, relay, fuse... who knows what until you check into it.If it doesn't start with starting fluid, check the spark. Pull a plug wire and attach it to a spare sparkplug and set the plug on a solid metal part of the engine. Have a helper crank the engine while you watch the plug. If you have a good spark, it might just be out of timing.In any case, you'll need to start isolating the problem. Find out which part isn't working then you'll know what to replace/repair.

Get a can of Starting fluid from the parts store and spray it into the air intake hose to the engine, if it fires up and stalls right away you have a fuel pressure issue, more than likely a defective electric fuel pump inside the gas tank.

spray a little bit of starting fluid in the throttle body it will start that means the injectors are not firing no power at injectors = bad crank sensor on top of driver side bell housing auto parts store has them about 40 dollars make sure you push and hold the new sensor in while you tighten the bolt they have a few thousands of an inch of adjustment on them and it makes a difference you will start but get miss fire codes like p0306 p0303 if it is not in all the way hope this helps you please rate my solution

If you think its fuel, spray some starter fluid inthe throttle body. If it fires up, you have a fuel problem, otherwise, check your spark plug wires, distributor cap and rotor. Also, check your fuses.

you may have bent the flex plate ring.so it might be to far away from the crank sensor air gap.