2003 Jeep Grand Cherokee

Scan for codes. A common problem is the crankshaft position sensor code P0320. It will cause it to lose spark and tachometer will drop suddenly, but it may restart later after it cools off. (Get to a repair shop.) You can scan by turning the ignition key from Off to On three times quickly without starting the engine. The codes will display at the odometer screen. Good Luck

Check for spark, remove a spark plug wire insert a screwdriver into the boot and then hold the metal part of the screwdriver 1/2 inch from a metal part of the block then have someone crank the engine while you watch. If you have spark and you know there is fuel at the proper pressure in the fuel rail. Unplug an injector then put a test light between the terminals then crank the engine if it flashes perform the injector flowtest.