Jeep

The easiest way to check fuel injectors is by using a multimeter. Disconnect the fuel injectors and attach the test leads to the male spade terminals. Measure the resistance (Ohms) of the injector. Ideally, you want to find out what the resistance should be from a manual (often it’s between 13.3 and 15.7 for V6 Jeeps), but if you can’t figure that out, there’s another way. Simply measure all of the fuel injectors. That way you’re getting a pretty decent estimate as to what the average reading should be and you can track down and isolate a single fuel injector should it deviate from the norm.
If the resistance is roughly the same for all fuel injectors (within the allowed tolerance), the problem’s not in the fuel injector. If one fuel injector reading deviates too much, you know that it’s faulty and that it needs replacement.
The second method requires a vehicle equipped with OBD II. Later model Jeeps have it, but make sure to check if yours does. The procedure is simple. You attach an OBD reader to the port and it tells you all of the faults (if there are any). In 90% of the cases with a faulty fuel injector it will print a misfire rather than just a code for a bad fuel injector (check to a manual or online guide for specific Jeep codes).