When mine did that it got progressively worse until it got so bad I had to do something about it. It turned out to be the PCM (ECU, computer). The check engine light should come on right away as a bulb check, it should not depend on any sensors or anything else. If you listen carefully next time, you will notice that as long as the check engine light does not turn on, the fuel pump will not begin priming. Once the light comes on, the fuel pump starts to prime and the Jeep starts and runs perfectly. I spent about a month checking and rechecking grounds and voltages but in the end the PCM had to be replaced, after that it has been fine for many months.