The Passport has one ignition coil per cylinder located on top of each spark plug. Each coil should have 12 volts to one of the wires at the coil when the ignition key is on or the engine is running. The ignition coil electrical circuit is completed by the fuel injection/ignition computer grounding the injector internally in the computer. The computer needs to receive inputs from several engine sensors (crankshaft position sensor, crankshaft position sensor ect....) it processes this information and then commands the ignition coil ground wire. A scan tool attached to the 16 pin socket under the dash may provide important information in diagnosing the problem. Was the Check Engine Light on prior to the engine losing spark or did the engine run poorly.