my 99 jeep xj starts up fine when sitting cold, but when sitting for 1+hours it wont start unless i give it gas. On top of that it will just die randomly with no struggle, i’ve got a newer battery that tested good voltage, replaced the crankshaft sensor, and it had a new fuel pump, thoughts?

 

I had a similar issue with my 1999 cherokee. I replaced my old stock 250k mile injectors with reman 4 hole bosch. Sitting overnight it would start fine, but if I let is sit for 30 minutes or more it wouldn't start unless I gave it some throttle. It turns out that my reman injectors were leaking down flooding the engine. I sent my injectors back for warranty and replaced with another set. My issue is now gone.

-Tmoney12

 

I think it's likely that you have two separate problems. One is that the vehicle starts poorly when warm. The other is that the vehicle dies randomly.

For the first, when it starts poorly when warm, when it does start, does it start CLEANLY or does it stumble a bit? If it stumbles, that indicates that you likely have an injector leaking raw fuel into the cylinders and it stumbles because it has to burn off that excess fuel. Noted by tmoney12 earlier post. If it starts cleanly when it does start, it may be that the coolant temperature sensor is giving improper input to the computer which controls the fuel/air mixture. That sensor is located on the thermostat housing, inexpensive and easy to replace. You can test them but they aren't very expensive so most just replace them if they are in question.

For the vehicle dying randomly, I would put a code reader or a scan tool on your OBDII port under the dash on the drivers side and see if there are any codes OR pending codes that might give you a clue as to where to look. If you have any codes, post the exact codes here (not just a description) for comment. You are losing spark or fuel, need to diagnose which component is failing.

Good luck and keep us updated!