You are buying 2x ZFR5N NGK SPARK PLUG FIT Jeep Cherokee XJ 4.0L MX MPFI,OHV,12V,131kW,301Nm 97-01. The workhorse, at the heart of smooth-running engines around the world. Spark Plug. SPARK PLUGS. Spark plugs are the "window" into your engine (your only eyewitness to the combustion chamber), and can be used as a valuable diagnostic tool.