The Siemens digital motor electronics (DME) engine management systems in BMW 6-cylinder engines control fuel supply, fuel injection, ignition and emissions. In these systems, also known as Motronic, an electronic microprocessor, the engine control module or ECM, processes a variety of sensor inputs to monitor engine and vehicle conditions. The ECM operates the engine in accordance with driver input. It has self-diagnostic capabilities in accordance with US-mandated on-board diagnostics (OBD-II) standards and stores fault codes known as diagnostic trouble codes or DTCs which can be accessed for troubleshooting purposes.
In the Motronic system idle speed, idle mixture and ignition timing are not adjustable. OBD-II standards require the engine to operate within extremely tight tolerances maintained by feedback loops in the electronics. These standards as well as upgraded manufacturing materials and techniques allow many automotive components to function well past times and mileages that were considered normal in previous decades. As examples, engine oil and spark plugs are capable of extended life compared to the past.
Replacing the spark plugs on your X3 is part of routine maintenance. BMW recommends replacing the spark plugs on X3 models every 100,000 miles. As mentioned above, with all the major engine and engine management design changes over the years, spark plugs now last up to three times as long as they did in years past. This is good and bad. It means you save money and time not having to service them so frequently, but run the risk of a spark plug seizing in the cylinder head. I suggest replacing your spark plugs every three years regardless of mileage. If the last time they were serviced is unknown, replace them right away.
Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches.
Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Never work on your vehicle if you feel the task is beyond your ability.
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BMW X3 models equipped with an M54 6-cylinder engine utilize an individual ignition coil for each spark plug, referred to as coil over plug (red arrows). When servicing your spark plugs be sure the engine is cool and leave yourself about an hour to do the job. Be careful not to drop a spark plug. If you do, replace it. The spark plug insulator can crack and can lead to an engine misfire. Remove the engine cover on the cylinder head. See our tech article on engine cover removing. This tech article shows X3 models with a M54 6-cylinder engine. Later 6-cylinder engines are similar.
Remove the ignition coil from the cylinder head by pulling it straight up. If the coil resists, twist it when pulling up to break it free from the spark plug. The ignition coil rubber boot can become stuck to the spark plug over time. You can also use a flathead screwdriver to lever the coil up and out of the cylinder head. Be very careful using this method as the coil is made of plastic and easily damaged.
Using a 5/8 thin-wall spark plug socket on a 12" extension (red arrow), remove the spark plug from the cylinder head. Late 6-cylinder engines: If your spark plug socket does not fit into the spark plug hole, you can remove the ignition coil insulator from the valve cover. Use 90 degree tip snap ring pliers to grab the insulator holes and squeeze. Then pull the insulator up and out of the cylinder head. This is for vehicles with plastic valve covers only. If you find that engine oil has contaminated the ignition coil boot or there is oil in the spark plug well (blue arrow), you will have to repair the oil leak and replace the ignition coil. The source of the oil leak will likely be the valve cover gasket.
If you are chasing a weird misfire or coils are failing multiple times, check that the coil grounds are secure and the terminals are in good shape (red arrows). I have seen these damaged or left loose from previous repairs.