Selling spark plugs for modern vehicles can be a demanding experience for today’s parts professionals. 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 understand the need for periodic spark plug replacements. For that reason, many spark plug replacements have become a major repair that often require two or three hours of time and a wide array of tooling to complete.
To illustrate, four years ago I recommended to a regular customer that he have the spark plugs changed in his Ford Expedition at the 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 the spark plugs were seized tightly into the engine’s aluminum cylinder heads.
My first step was to recover a diagnostic trouble code (DTC) from the powertrain control module’s (PCM’s) diagnostic memory. The only DTC contained in the memory was a P0303, indicating a misfire on number three cylinder. The flashing check engine light indicated that the misfire on number three cylinder was a “type A” misfire that required immediate attention because, if raw fuel from the misfiring cylinder was passing into the exhaust gas stream, the catalytic converter would eventually fail due to overheating.
Although some exceptions exist, most manufacturers of 1996 and newer vehicles specify replacing spark plugs at 100,000-mile intervals. The exceptions might include 30,000-mile intervals on some domestic and import vehicles and 140,000 intervals on some hybrid vehicles.
But a technician becomes involved with a special set of conditions when a vehicle like our Ford Expedition rolls in with 155,000 miles on the odometer. Without a doubt, all of the spark plugs will need replacement, all spark plug wires will be seized to the spark plugs, and the spark plugs will be seized into the aluminum cylinder head.
SPARK PLUG REPLACEMENT TIPS
When selling spark plugs, keep in mind that spark plugs are now designed to not only last 100,000 miles, but also to be successfully removed at the same mileage. Unlike the Expedition’s standard original equipment spark plugs, modern spark plugs are plated with metals that resist seizing to aluminum cylinder heads.
But the real issue in spark plug removal is avoiding tearing the spark plug threads away from the cylinder head. Although tool manufacturers make spark plug thread repair kits, the difficulty with repairing threads is the lack of accessibility to the spark plugs.
Patience is always the key to removing seized spark plugs. Because the spark plugs now reside in a well drilled about five inches into the cylinder head, it’s important to blow loose dirt out of the spark plug well with compressed air before removing the spark plug. As always, safety glasses should be worn to prevent injuries to the eyes.
Next, soak the spark plug with high-quality penetrating oil and loosen the spark plug about one-eighth turn to allow the penetrant to soak into the carbon build-up on the lower spark plug threads. After soaking for 30 minutes, gently alternate between tightening and loosening the spark plug. If the spark plug still feels tight, apply more penetrant, allow it to soak as long as necessary and repeat the procedure until the spark plug frees itself from the cylinder head. These basic suggestions can save your retail customer the potential cost of removing, repairing and replacing a cylinder head.
CHOOSING THE RIGHT PLUG
Speaking from the professional point of view, it’s far more cost-effective to install an original equipment (OE) or OE-equivalent spark plug than it is to risk creating a cylinder misfire or ruin a cylinder head by installing a cheaper substitute. In today’s market, your customers might find themselves choosing between a standard spark plug and various types of more expensive spark plug electrode designs, precious metal platings and heat ranges.
To explain the differences, standard spark plugs are designed to last for only 30,000 miles in older engines with cast-iron cylinder heads. For this reason, they don’t need exotic electrode designs and expensive gold, platinum or iridium platings on the electrodes. In direct contrast, modern spark plugs are designed to last 100,000 miles.
For ease of removal, the threads on modern long-life spark plugs are plated with nickel and other metals to resist seizing to aluminum cylinder heads. They also have their electrodes plated with various gold, platinum and iridium alloys to resist erosion caused by high-combustion chamber temperatures. And due to the heat transfer capabilities of their electrodes and insulator designs, modern spark plugs are also designed to operate under a wider range of combustion chamber temperatures found in modern engines.
Because the Ford Expedition uses a distributorless ignition, a “double platinum” design is required, which means that both the center and ground electrodes are plated with precious metals. Both electrodes must be plated because half of the spark plugs fire on negative electrical polarity and the remainder on positive electrical polarity. Older engines with distributor ignitions fire on normal polarity can use a “single platinum” spark plug, which means that only one of the electrodes is plated. For this reason also, a single-plated spark plug should never be substituted for a double-plated version.
INSTALLING SPARK PLUGS
To prevent cylinder head damage and engine misfires, modern spark plugs require correct installation techniques. Because contaminants can conduct high-voltage spark, it’s important to keep the spark plug insulator free of oil or greasy fingerprints by inserting the spark plug into a short length of 5/16-inch fuel hose or a dedicated spark plug holding tool. Before installation, make sure that the spark plug air gap meets manufacturer’s specifications.
Next, make sure the cylinder head seating surface is free of dirt. Dirt caught under the spark plug gasket or tapered seat will allow combustion gases to leak from the cylinder. Always torque a spark plug to specification. Most modern spark plugs require only about 7 to 15 foot-pounds of torque to ensure correct seating. Excessive torque can damage the spark plug threads while insufficient torque will cause the spark plug to overheat and damage the engine.
SELL THE RELATED PARTS
All too often, technicians and retail customers forget that spark plug wires and coil boots wear out along with the spark plugs. After 100,000 miles of hard use, spark plug wire boots tend to stick firmly to spark plug insulators. For this reason, spark plug wires and boots are often damaged when they are removed from the spark plug. In addition, spark plug wires tend to lose their insulating capacity because of perforations in the wire’s insulation or the wire being soaked with oil and other solvents. In contrast, coil-on-plug boots tend to develop carbon tracking or “flashovers” on their inner diameters when a spark plug wears out. In this case, installing an old boot with a flashover mark inside will cause the new spark plug to misfire. Most coil-on-plug boots are replaceable and should, for this reason, be replaced with the spark plugs. Selling wires and boots is not only good preventive maintenance, it helps prevent expensive comebacks and definitely helps restore profits to the bottom line.
COMPLETING THE JOB
Remember that selling spark plugs is only part of any 100,000-mile maintenance plan. In most cases, the throttle plate should be cleaned of carbon and sludge by using an aerosol throttle body cleaner designed for the purpose. Similarly, because the air filter assembly is usually removed for spark plug replacements, don’t forget that the air filter should be inspected and, if it’s a high-mileage vehicle, the mass air flow sensor should be rinsed off with an aerosol mass air flow sensor cleaner designed for that purpose. Last, don’t forget to recommend replacing the fuel filter if required. Recommending these services to your retail or wholesale customers will add value and performance to an otherwise expensive spark plug replacement.