一辆帕萨特 B4乘用车,当累计行程为34万 km 时,出现发动机怠速不稳,有时会自动熄火,熄火后有时能够顺利起动,有时需起动多次才能着火。首先按常规检查真空管路、怠速控制装置和点火正时,未发现问题。当时由于手上没有故障检测仪,因此无法进行故障查询,于是就凭经验进行了相关检修。先后更换了火花塞、分缸线、分火头和分电器盖等,但故障现象无任何好转。最后更换了分电器总成,并重新校验了点火正时,发动机怠速运转平稳。于是进行路试,当乘用车行驶在高低不平的路面上时发动机突然熄火,重新起动多次后发动机才勉强着火。检查各线束连接器的连接情况,未发现问题。对造成该起故障的原因进行了认真分析,认为:当发动机在工作时丢失曲轴位置信号,发动机 A Passat B4 passenger car, when the cumulative travel of 340,000 km, the engine idling instability, and sometimes automatically turn off, sometimes after the flame can start smoothly, and sometimes need to start several times in order to catch fire. First check the vacuum line routine, idle speed control device and ignition timing, did not find the problem. At that time, because there was no fault detector on hand, it was unable to carry out fault inquiries. Therefore, the relevant maintenance was carried out empirically. Has replaced the spark plug, sub-cylinder line, sub-fire head and distributor cover, etc., but the failure phenomenon without any improvement. Finally replaced the distributor assembly, and re-calibration of the ignition timing, the engine idle speed stable. So the road test, when the passenger car driving on rough terrain the engine suddenly turn off, re-start the engine only reluctantly caught fire. Check the harness connector connection, no problems found. The reasons for the failure caused by a careful analysis that: when the engine loss of crankshaft position signal at work, the engine