How Do I Know If My Distributor Cap And Rotors Are Bad

Posted in Ignition Systems
  • I have a 1994 LS400 and I get all of 12mpg and I was going through a normal tuneup checklist and need to know how to tell if my distributor cap and/or rotors are bad. Money, with a 4.0 liter V8, is tight and prevents me from going out and buying the replacements without need, so I need a method with which to find out if they are bad.

    There are 3 Answers for "How Do I Know If My Distributor Cap And Rotors Are Bad"

    1. gremlingts says:

      If the contacts inside the cap have deep pits, then it’s time to replace it. Otherwise, it can be cleaned up and reused. Same with the rotor. Also look for carbon tracking between the plug towers inside the cap, if you see a dull line of burnt plastic going between two towers, then replace the cap. I don’t think there’s any feeler-gauge check , since it’ d be impossible anyway. Just do a visual check, and if it appears ok, then just clean and reuse.

      - The Gremlin Guy – 4.2 straight 6 Gremlin

    2. Tee says:

      The internal condition is what goes bad. The ignition spark jumps from the rotor to the internal contacts and causes corrosion and pitting. The contact between the cap and the rotor in the center of the cap also can wear. Other problems are caused by moisture and the spark can travel across the cap and ground out the spark.

      You can clean the contacts with a wire brush and wash the inside out with iso alcohol to get you by. Be careful with the center contact, it is usually made of carbon and can be damaged.

    3. 45 cal says:

      Check for carbon build up on the pronges inside the cap & rotor if waren replace as a unit don’t just put 1 in>