Engine light on and bad gas milelage

Well for sure there is a problem and your vehicles computer has detected it which is a good thing. Most of your local auto part stores will pull disgnostic trouble code's (DTC's) for free. Now they do this and try to just go ahead and sell you a part/sensor but I would suggest fully diagnosing the problem before purchasing any parts. I would suggest going and getting any DTC's and then post on here or you can reply/comment on this posting. Ince you get the DTC(s) it will be much easier to help you diagnose the problem because at this point I have no idea where to begin because it could be MANY things that can cause this. If you have the 4.0 liter engine I can tell you a common problem with them. If you happen to get a DTC of P0171 or P0174 (like I said is common) that is saying that your vehicles computer has detected from the oxygen sensors detected a lean burning condition. When your computer gets this problem it makes your fuel injectors stay open for a longer period because it thinks it's not getting enough fuel so your getting more fuel then you really need because in most cases one of the oxygen sensors is faulty and sending the wrong signal the the computer. Now that's not a 100 percent thing as far as a faulty oxygen sensor as a vacuum leak can cause the same thing. That's where properly diagnosing the problem before replacing any parts is so important so you're not wasting money on parts that you don't need and can't return. These codes may not even be close to the problem and was just using those DTC's because they are common with the 4.0 liter in Jeeps. Once you get the DTC(s) you can also email me directly with them if you want and I'll be happy to help you to diagnose the problem. My email is [email protected] and no there won't be a cost to you if you email me directly. Hope I was able to help a little any way with what information you provided.

Tune up is needed