Spark plug replacements can be simple, however, if done improperly it can result in engine misfires, poor fuel economy, and potential malfunctions. That said, following the basic steps of spark plug replacement will ensure an efficient and successful job.
Before diving into the details, it is important to understand how spark plugs work. Spark plugs are made up of electrodes, a seat, a resistor, a ceramic insulator, and a core. These parts are crucial to engine performance as the spark plugs can wear down—resulting in a lack of power, poor engine performance, rough idling, or an engine light coming on. When customers come into the shop experiencing these issues, technicians can expect to find problems with the spark plugs.
That said, any good repair starts with a diagnostic scan to identify DTC codes across the vehicle's systems. Many tools, including the Bosch ADS series scan tools, can complete whole vehicle pre-scans in as little as 60 seconds, making it an easy first step to confirm a technician's suspicions about a specific issue and identify other potential malfunctions within the vehicle.
Once the scan is complete and suspicions have been confirmed, the technician can go under the hood and begin the spark plug replacement. Any technician looking to complete this job efficiently will need the right tools including:
- Spark plug socket
- Spark plug gap gauge
- Torque wrench
- Extension bar
- Offset boot removal pliers
- Ignition coil puller
Once you have your tools ready, it is time to get the parts in order. Since every car has different specs, it is crucial to know which spark plugs are compatible with the vehicle you are working on. This information can usually be found in the car's owner's manual and online at retail and manufacturer's built-in "Does it fit" functions. While each plug has similar internals, there are four popular types including copper, platinum, doubled platinum, and iridium. All these spar plugs range in durability and ignitability, and if the wrong spark plug is installed, it could result in issues including engine misfires, poor gas mileage, and slow acceleration.
After getting all the tools and the right parts together, we can begin the repair.
Replacing each spark plug is straightforward. Once the technician locates each spark plug location on the engine by following the spark plug wires or locating the individual ignition coils, they can begin the process.
After removing the spark plug wire boot or ignition coil from the cylinder, "you might need to use your offset boot removal pliers to assist in removing the boot from the spark plug," the technician can then remove the old spark plug with the ratchet wrench, which is affixed with the spark plug socket and extension bar. Once removed, a quick visual inspection is recommended to see if any damage has occurred to the spark plug. Common visual indicators of damage include rust on the terminal nut (located on the top of the spark plug), or the inside of the spark plug wire, cracks in the ceramic insulator, and a dirty or eroded electrode preventing the spark plug from being produced effectively.
Once removed, you can take the new spark plug and after checking the plug gap with your plug gap gauge, adjust it to the correct gap recommended by the vehicle manufacturer. Spark plugs are typically designed to have a spark gap which can be adjusted by the technician installing the spark plug, by the simple method of bending the ground electrode slightly to bring it closer to or further from the center electrode. Once the gap is correct, insert it into the cylinder using the socket wrench and spark plug socket—making sure to tighten the spark plug correctly, first by hand "to avoid cross-threading" and then finishing with the Torque wrench and torque to the correct spec. Overtightening can strip the treads and make future replacements difficult, and under-tightening could result in the plug coming loose and blowing out of the engine's cylinder. Finally, if you are not replacing the spark plug wires, just insert the boot into the cylinder until you hear it click onto the spark plug, signaling the connection is secure and the job is done. Then you repeat the process with the remaining spark plugs—making sure to remove any other parts that are in the way like the intake cover to gain access to the other cylinders.
If you are replacing the spark plug wire, an effortless way to ensure you are matching the length is to lay out all your new wires in front of you and organize them by size. You can then line up the old wire to the new one when you remove it from the vehicle to ensure each wire is the proper size.
Understanding the details of any repair, engine-related or not, enables technicians to work efficiently and communicate confidently with customers. While spark plug replacement is straightforward, a deeper knowledge of the tools and parts involved enhances service efficiency and helps build customer trust.
