GM Buick/Oldsmobile/Pontiac/Full-Size 1975-1990 Repair Guide

Spark Plug Wires

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TESTING



See Figure 1

Every 10,000 miles, inspect the spark plug wires for burns, cuts, or breaks in the insulation. One way to check for "leaking" wires is to lightly spray them with water, start the vehicle, and watch for tiny sparks around the wires (it is easiest to see them at night). If you see sparks, replace the wires as this can cause rough idle and misfire, especially in damp weather. Check the boots and the nipples on the distributor cap. Replace any damaged wiring.

Every 30,000 miles or so, 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. Generally, the useful life of the cables is between 45,000-60,000 miles.

To check resistance, remove the distributor cap, leaving the wires in place. Connect one lead of an ohmmeter to an electrode within the cap; connect the other lead to the corresponding spark plug terminal (remove it from the spark plug for this test). Replace any wire which shows a resistance over 30,000&omega. Generally speaking, however, resistance should not be over 25,000&omega and 30,000&omega must be considered the outer limit of acceptability.



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Fig. Fig. 1: Acceptable limits for plug wire resistance

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

REMOVAL & INSTALLATION



See Figures 2, 3 and 4

To avoid confusion, replace spark plug wires one at a time.

To remove the wires, twist and pull the boot off of the spark plug and the distributor terminal.

When installing new wires, replace them one at a time to avoid mix-ups. Start by replacing the longest one first. Install the boot firmly over the spark plug. Route the wire over the same path as the original. Insert the nipple firmly onto the tower on the distributor cap, then install the cap cover and latches to secure the wires.



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Fig. Fig. 2: In most cases, it will be necessary to remove the retainer ring to replace the spark plug wires



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Fig. Fig. 3: Always label the terminal and wires to ease installation



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Fig. Fig. 4: Replace one wire at a time to avoid confusion

 
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