GM Full Size Vans 1987-1997 Repair Guide

Spark Plug Wires

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TESTING



See Figures 1 and 2



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



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Fig. Fig. 2: Checking individual plug wire resistance with a digital ohmmeter

At every tune-up/inspection, visually check the spark plug cables for burns cuts, or breaks in the insulation. Check the boots and the nipples on the distributor cap and/or coil. Replace any damaged wiring.

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.

To check resistance:

  1. Remove the engine cover to gain access to the distributor.
  2.  
  3. Remove the distributor cap, leaving the wires in place.
  4.  
  5. Connect one lead of an ohmmeter to an electrode within the cap.
  6.  
  7. Connect the other lead to the corresponding spark plug terminal (remove it from the spark plug for this test).
  8.  
  9. Replace any wire which shows a resistance over 30,000 ohms. Generally speaking, however, resistance should not be over 25,000 ohms, and 30,000 ohms must be considered the outer limit of acceptability.
  10.  

It should be remembered that resistance is also a function of length. The longer the wire, the greater the resistance. Thus, if the wires on your van are longer than the factory originals, the resistance will be higher, possibly outside these limits.

  1. Install the engine cover.
  2.  

REMOVAL & INSTALLATION



See Figures 3 and 4



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Fig. Fig. 3: Remove the engine cover to gain access to the distributor, then disengage the wires from the distributor:



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Fig. Fig. 4: Disengage the spark plug wires from the plugs. They can be accessed either through the panel at the wheelwell or at the engine cover (as shown)

When installing new wires, replace them one at a time to avoid mix-ups. Start by replacing the longest one first.

  1. Remove the engine cover to gain access to the distributor.
  2.  
  3. Remove the spark plug wire by gripping the boot firmly and disengaging the wire from the spark plug and the distributor.
  4.  
  5. Install the boot of the new wire firmly over the spark plug. Route the wire over the same path as the original.
  6.  
  7. Install the engine cover.
  8.  

 
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