On average, the cost for a Jeep Grand Cherokee Smoke from engine or exhaust Inspection is $80 with Bad fuel pressure regulator: A vehicle’s fuel system is designed to work within a specific range of pressure, which is controlled by a fuel pressure regulator. If the regulator is on the fritz, the pressure will fluctuate outside of the system’s specified range. If it falls too low, there may not be enough fuel reaching the engine to start it. Too much pressure may result in over-fueling, which can make your engine run rough and deliver poor fuel mileage, among other things. The remedy is to replace the fuel pressure regulator. for parts and $80 for labor. Prices may vary depending on your location.