Just want to know what causes the problem. While driving the tachometer goes to zero a hesitation in engine occurs but it continues to run. After stopping and turning off the ignition and restarting, the tachometer works and engine performance is fine. This sequence has happed many times. However the last time the engine quit completely. after coasting to a stop and turning the ignition off I was able to restart, as previously, the tachometer works and engine performance is normal.