The mileage is about 100 thousand km, the 2009 Ford Carnival cars equipped with 1.5L engine and 4 speed automatic transmission. The car will be shut down occasionally because of engine idling. According to the driver, the car sometimes stops at the intersection when the traffic lights are waiting. After receiving the car: the commissioning test verifies the failure, and the fault does exist. The engine started normally and idling was stable, and the engine suddenly stalled after idling about 15min. After the engine is flameout, the engine is restarted and the engine can start smoothly. The driver was asked to know that the car had been checked out in other repair plants, cleaned the intake manifold, the injector and the engine combustor, changed the engine control module (PCM) and the electronic throttle (ETC), and replaced the spark plug, the gasoline pump, the gasoline filter, the air filter, and the air flow. Sensors (MAF) and other failures are not excluded. Connect IDS to read fault code, trouble free code store, view related data stream, and do not find any abnormal data. So the maintenance personnel decide to start the engine, carefully observe the running state of the engine when the engine is extinguished, and analyze and compare the data when the engine is caught by the IDS. (IDS has the specific data acquisition function. As long as the conditions for data acquisition are completed, IDS will automatically complete the right Data acquisition for setting conditions. Set up the IDS, start the engine, stand in front of the vehicle to observe the engine's running state. When the engine is running for about 2 min, the "front" side of the engine room will generate a loud noise. Continuous observation found that every 1 min about the front right side of the engine room will make a loud noise. After careful observation, the sound is generated by the spark between the crankshaft pulley tooth (crankshaft position sensor signal tooth) and the timing chain end cover. In order to accurately determine the specific position of the spark from the crankshaft, the maintenance personnel guide the fire experiment with a wire, and the end of the wire is iron and the other end is close to the inner and outer ring of the crankshaft with the premise of safety. Finally, the spark is emitted from the outer ring of the crankshaft pulley, while the inner ring of the crankshaft pulley does not spark. It should be the rubber torsional shock absorber between the inner and outer rings of the crankshaft belt to play the role of insulation. In addition, the maintenance personnel also notice that the engine runs very normally when using the wire to connect the outer ring of the crankshaft to the fire. After careful analysis, the cause of the sudden ignition of the engine is that the electromagnetic interference produced by the spark affects the signal of the crankshaft position sensor, and the cause of the spark may be related to the drive belt. In order to determine the cause of the spark, the maintenance personnel decided to dismantle the transmission belt and carry out the experiment. Before dismantling, the maintenance personnel checked the scale line on the belt tensioner, in the normal range; then the engine was started after the drive belt was dismantled. The engine runs about 10 min, and no spark has been produced. It can be deduced that the spark is the static electricity produced by friction between the belt and the crankshaft pulley. Troubleshooting: after changing the belt, road test is done, everything is normal, so the car is returned to the driver. One month later, a telephone return visit was made, and the fault did not appear again. Maintenance summary: the scale line of the transmission belt tensioner is in the normal range, but because the belt has already run about 100 thousand km, the plasticity of the drive belt becomes poor, and the belt and the crankshaft pulley have slight skidding when the engine runs, and the rubber (belt) and the metal (crankshaft pulley) are caused by friction. Electricity, when the charge accumulates to a certain value, will break through the air to create sparks, and produce a loud noise. The spark will produce electromagnetic interference to the position sensor of the crankshaft, which causes the PCM to receive the incorrect engine speed signal and make the engine suddenly extinguish. And when the engine is started again, the electrostatic energy is low, it is not enough to form the electromagnetic interference, and the engine can work for a long time.