GM S-Series Pick-ups and SUV's 1994-1999 Repair Guide

Spark Plug Wires

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TESTING



See Figures 1 and 2



Click image to see an enlarged view

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 on models with a distributor:

  1. Remove the distributor cap, leaving the wires in place.
  2.  
  3. Connect one lead of an ohmmeter to an electrode within the cap.
  4.  
  5. Connect the other lead to the corresponding spark plug terminal (remove it from the spark plug for this test).
  6.  
  7. 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.
  8.  

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 truck are longer than the factory originals, the resistance will be higher, possibly outside these limits.

To check resistance on models with a distributor:

  1. Tag the wires, then remove the wires one at a time from the spark plug and the coil pack. To access the wires at the coil pack, raise the front passenger side of the vehicle, support it with jackstands and remove the passenger side tire. The coil pack and wires can now be reached through the opening in the wheel well.
  2.  
  3. Connect one lead of an ohmmeter to one end of the wire and the other lead to the other end of the wire.
  4.  
  5. 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.
  6.  

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 truck are longer than the factory originals, the resistance will be higher, possibly outside these limits.

REMOVAL & INSTALLATION



See Figures 3 and 4



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Fig. Fig. 3: Removing the spark plug boot from models equipped with a distributor



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Fig. Fig. 4: Mark the spark plug wire and coil pack prior to disconnecting the wire, this will make installation easier-models equipped with a distributorless ignition system

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

  1. Remove the spark plug wire by gripping the boot firmly and disengaging the wire from the spark plug and the distributor or coil pack. To access the wires at the coil pack, raise the front passenger side of the vehicle, support it with jackstands and remove the passenger side tire. The coil pack and wires can now be reached through the opening in the wheel well.
  2.  
  3. Install the boot of the new wire firmly over the spark plug. Route the wire over the same path as the original.
  4.  

 
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