Volvo 240/740/760/780/940/960 1990-1998

Spark Plug Wires

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TESTING



See Figures 1 and 2

Visually inspect the spark plug cables for burns, cuts, or breaks in the insulation. Check the spark plug boots and the nipples on the distributor cap and coil. Replace any damaged wiring. If no physical damage is obvious, the wires can be checked with an ohmmeter for excessive resistance.

Every 50,000 miles (80,000 km) or 60 months, the resistance of the wires should be checked with an ohmmeter. Wires with excessive resistance will cause misfiring, and may make the engine difficult to start in damp weather.

  1. Remove the spark plug wires one at a time.
  2.  
  3. Measure the length of the spark plug wire with a suitable tool. Write down the length.
  4.  
  5. Connect one lead of an ohmmeter to one end of the spark plug wire on the metal conductor, and the other lead to the other end.
  6.  
  7. Replace any wire which shows over 5,000-7,000 ohms per foot.
  8.  



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Fig. Fig. 1: Checking plug wire resistance through the distributor cap with an ohmmeter