Diagnostic Tips

Checking Spark Plug Wires

Worn or damaged spark plug wires can cause engine misfire that could result in engine starting difficulty, rough idle, lack of acceleration, engine bucking, lower fuel mileage and excessive emissions. Shown below are some techniques to determine whether it is necessary to replace the spark plug wires:

Visual Inspection (Engine On)

Look at the wires and listen for any sign of:

Make sure there is no intermittent spark occurring anywhere along the exterior of the spark plug wires. This is typically seen as a short blue spark and heard as a cracking or snapping noise. Pay particular attention to points along the spark plug wire that are close to ground planes or other wiring.

Visual Inspection (Engine Off)

Look at the wires and listen for any sign of:

Make sure the wire, boots, and nipples are not caked with oil, grease and dirt.


Make sure the wire, boots, and nipples have no burns, cracks, chafing, or obvious signs of damage such as cuts, swelling, etc. Visually compare to each other to note potential damage.

Electrical Tracking

Make sure the boots, spark plugs, performance ignition wires, nipples, and wire to coil/distributor tower show no signs of tracking. Tracking is most commonly seen as a thin erratic burn line on:

Arcing to Grounds

Make sure the spark plug wires are not arcing to any ground plane such as an exhaust manifold, engine bracket, heater hose, etc. Spark plug wires should not be in contact or within 1/2" of any ground plane.

Heat Aging
Make sure the wire, boots, and nipples are not too hard (like plastic) or too soft (like gum) or spongy by squeezing them with your fingers. These rubber components should feel firm, like a pencil eraser.

Open Circuit / Heat Resistance
Make sure the spark plug wire does not have an open circuit, and as a general rule, the resistance should not exceed 1,000 ohms per inch (but may be permissible by some O.E. manufacturers' specifications). To check, perform the following steps:

If any of the conditions noted above exist, replace the spark plug wire and follow the installation instructions located inside your new ProConnect™ Spark Plug Wire Set.