Agree with SuperJ that you will need someone who has experience with a diesel jeep or diesels in general but if you can find the water separator on the fuel system , there should be a sensor on it that tells you when the filter element is saturated and needs to be serviced or changed . I'm not a diesel mechanic but I've seen these sensors on trucks and buses so it's likely there is a sensor of this nature and there must be a water separator since all modern diesel fuel systems have them. You'll need a maintenance manual .