When The Spark is Gone

Replacing spark plugs in modern vehicles can be a demading experience for today’s technicians. Not only have spark plug designs changed, the ignition systems that create the spark have changed as well.Because modern engines run so well for so long, many customers have either forgotten or fail to understnad the need for periodic spark plug replacements. For that reason, many spark plug replacements have become a major repair that often requires two or three hours of time and a wide array of tooling to complete.

To illustrate, four years ago I recommended to a regualr customer that he have the spark plugs changed in his Ford Expedition at hteh recommended 100,000-mile interval. Unfortunately, the engine continued to perform well and the spark plugs were never replaced as recommended. Last month at 155,000 miles, the customer reported that his check engine light had begun flashing and that the engine was losing power. Given the advanced mileage, it was nearly certain that he spark plugs were seized tightly into the engine’s aluminum cylinder heads.

My first step was to recover a diagnostic trouble code from the powertrain control module’s diagnostic memory. The only code obtained in the memory was a P0303, indicating a misfire on number 3 cylinder. The flashing check engine ligh indicated that the misfire on number three cylinder was a “type A” misfire that required immediate attention because, if raw fuel from teh misfiring cylinder was passing into the exhaust gas stream, the catalytic converter would eventually fail due to overheating