and, as a quick check, have someone turn the key while you push on the ecu cover. the ecu is in front of the passenger, but in the engine bay. they are well known to develop bad connections, both of my zj grand Cherokees did it. one, I was able to take care of it by putting some pieces of wood on the side of the ecu and zip tying them to the ecu. the other required me to buy an ecu. I got one on ebay for 50bucks and the jeep never had trouble again