One of the most fundamental tune-up procedures on a BMW is replacement of the spark plugs. BMW plugs should be inspected regularly and replaced if necessary. Most BMWs made from the early 1990s and later utilise a coil-on-plug set-up that does not use conventional spark plug wires. BMW spark plugs should be changed every 10,000 miles or once a year. This is an easy task to perform with the right tools and approach.
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Things you need
- Socket set and ratchet
- Spark plug wrench
- Spark plugs
- Torque wrench
Ensure that the motor is cold. If the car has recently been driven, allow it to cool down enough that you can touch the motor. This will avoid causing problems between the threads of the spark plug and the threads of the aluminium cylinder head.
Remove the engine cover(s). Carefully pry up the plastic plugs on top of the engine cover(s) with a flat head screwdriver. Under the cover(s) are the nuts that hold the cover(s) on. Remove these with a socket. Engines with six cylinders or more have more than one cover while four cylinder models have one.
Detach the metal retaining rings that hold the wires to the coils by prying them off with a screwdriver. Manoeuvre the wires out of the way so that you can remove the coils.
Remove the coils by unbolting the two nuts that hold them to the valve cover. Take note of any ground straps bolted to the studs that the nuts go on. These need to be reinstalled correctly. Set the coils aside once they are removed.
Locate the spark plugs in the hole that the coils sit over. Wipe up any excess oil around the spark plugs with a paper towel or a rag. Insert the spark plug wrench into the hole until you feel it seat on the spark plug. Spark plug wrenches have a rubber insert that grips the end of the plug, allowing you to loosen it. Turn the wrench counterclockwise to loosen the plug and remove it from the engine.
Measure the spark plug gap on the new plugs and adjust them, if needed, with a plug gapper to make sure that they are within the recommended specifications. Use the shop manual for the specific settings for your BMW model.
Insert the plugs into the plug wrench then thread them into the cylinder head one at a time. Make sure that you do not cross-thread the plugs as you tighten them into the engine block. Use a torque wrench to tighten the plugs to the proper torque setting for your model of BMW.
Replace the coils, ensuring that the small ground straps are properly installed. Reattach the coil connectors. Bolt the engine cover(s) back on and install the plastic plugs.
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