The wire on the right was returned
by a customer because the vehicle was running poorly. It is from
a 4WD vehicle with a 16 valve SOHC engine used off-road, and is
typical of what occurs when preventive maintenance is neglected,
or not properly performed on this style of vehicle.
Diagnosis by automotive technician:
Diagnosis by Magnecor:
This vehicle has been driven through lots of water and mud and, over time, a large amount of water has collected in one or more of the spark plug holes. The discoloration of the spark plug connector indicates the water level may have reached the top of the spark plug hole in which it was situated. Spark plug wire connectors are not designed to operate under water, and on this vehicle severe arcing into the water no doubt occurred, causing the engine to misfire. Another connector not affected by this problem is shown on the left.
All multi-part spark plug wire connectors are vented to prevent them from popping off the spark plug as the engine heats up. Therefore, each and every time the engine cools, moist air is drawn through the tiny vent holes and a little condensation forms inside the spark plug holes -- more so in humid climates and during rainy seasons. Generally, most of the moisture condensing in spark plug holes (there is no drain) will evaporate out through the vent holes (in the top seal of the connectors) after the engine heats up. In vehicles that are driven through water, a great amount of water will flow over the engine and spark plug connectors, and a certain amount will pass through the vent holes into the spark plug holes. Unfortunately, as vehicles age, dirt and oil accumulates around the engine and over the connector covers, and if the valve cover gasket needs replacing, oil will leak into spark plug holes to make matters even worse.
The spark plug wire shown on right cannot be repaired and needs to be replaced. Had the spark plug connectors on this vehicle been regularly removed and the accumulated moisture (and oil) around the spark plugs removed, no failure would have occurred. If you run your vehicle through a lot of water, you need to remove any water from in and around spark plug holes as soon as possible. If you notice an engine miss or hesitation (particularly when the ignition system is under load at low speeds), you should have the problem investigated as soon as possible, because water (and/or oil) in the spark plug holes may be the cause.
More information relating to this subject is available on our FAQ, specifically:
Why are sparks jumping from boots and cable jacket ? (question 14)
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