Fuel Injectors rarely go bad, but when they do, they will cause the engine in your Jeep 4.0L Grand Cherokee (or Cherokee or Wrangler) to miss and/or idle rough. The really cool thing is that they can be easily tested with a multimeter and this article will show you how to do a simple Fuel Injector resistance test. Depending on the year of your specific Jeep (1995 and newer), a BAD Fuel Injector may or may not set a specific Fuel Injector Diagnostic Trouble Code (DTC) like: P0201, P0202, P0203, P0204, P0205, P0206. In most cases, all you’ll see Code-wise are Misfire Codes: P0300, P0301, P0303, P0304, P0305, P0306.