Abstract: A detector for detecting a secondary voltage supplied to a spark plug of an engine comprises a rubber tube mounted on a high tension cord and equipped with a detecting electrode, and a shield case or shield layer enclosing the rubber tube. The rubber tube is made up of first and second semicylindrical rubber members joined together into a tubular shape. The detecting electrode is U-shaped and has a middle portion embedded in the first rubber member and left and right ends which project, respectively, from left and right joint surfaces of the first rubber member, and are sheathed in grooves in left and right joint surfaces of the second rubber member. A lead wire is connected to one of the left and right projecting ends of the detecting electrode. This structure of the secondary voltage detector can facilitate the production process.

Abstract: A misfire detecting device for a double-ended distributorless ignition system is provided. The device includes a pulse generating circuit for generating a positive polarity pulse which is not so high as to cause spark discharge during the time after completion of spark discharge and before beginning of application of an ignition high voltage for next spark discharge. A reverse current preventing diode is connected at an anode to an output end of the pulse generating circuit and at a cathode to a positive polarity side of a secondary winding of an ignition coil. A plug voltage dividing circuit for dividing a plug voltage is connected between a center electrode and an outer or ground electrode of each of spark plugs to obtain a divided voltage. A detecting circuit detects a misfire of the spark plugs on the basis of an attenuation characteristic of the divided voltage after application of the positive polarity pulse.