Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSSUBARU2012IMPREZA WRX STI F4-2.5L DOHC TURBOREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTIGNITION SYSTEMSPARK PLUGTESTING AND INSPECTION
2012 Subaru Impreza WRX STI F4-2.5L DOHC Turbo
Spark Plug: Testing and Inspection
2012 Subaru Impreza WRX STI F4-2.5L DOHC TurboSECTION Testing and Inspection
Spark Plug
INSPECTION
1. Check the spark plug for abnormalities. If defective, replace the spark plug.
2. Check the spark plug electrode and condition of the insulator. If abnormal, check and repair the cause and replace the spark plug.
1. Normal:
Brown to grayish-tan deposits and slight electrode wear indicate correct spark plug heat range.
2. Carbon fouled:
Dry fluffy carbon deposits on insulator and electrode are mostly caused by slow speed driving in the city, weak ignition, too rich fuel mixture, etc.
3. Oil fouled:
Wet black deposits show oil entrance into combustion chamber through worn piston rings or increased clearance between valve guides and valve stems.
4. Overheating:
A white or light gray insulator with black or brown spots and bluish burnt electrodes indicate engine overheating, wrong selection of fuel, or loose spark plugs.
3. Using a nylon brush, etc., clean and remove the carbon or oxide deposits from the spark plug. If deposits are too stubborn, replace the spark plugs. After cleaning the spark plugs, check the spark plug gap "L" using a gap gauge. If it is not within the standard, replace the spark plug.
NOTE:
- Never use a plug cleaner.
- Do not use a metal brush as it may damage the electrode area.
Spark plug gap L: Standard 0.7 - 0.8 mm (0.028 - 0.031 in)
INSPECTION
1. Check the spark plug for abnormalities. If defective, replace the spark plug.
2. Check the spark plug electrode and condition of the insulator. If abnormal, check and repair the cause and replace the spark plug.
1. Normal:
Brown to grayish-tan deposits and slight electrode wear indicate correct spark plug heat range.
2. Carbon fouled:
Dry fluffy carbon deposits on insulator and electrode are mostly caused by slow speed driving in the city, weak ignition, too rich fuel mixture, etc.
3. Oil fouled:
Wet black deposits show oil entrance into combustion chamber through worn piston rings or increased clearance between valve guides and valve stems.
4. Overheating:
A white or light gray insulator with black or brown spots and bluish burnt electrodes indicate engine overheating, wrong selection of fuel, or loose spark plugs.
3. Using a nylon brush, etc., clean and remove the carbon or oxide deposits from the spark plug. If deposits are too stubborn, replace the spark plugs. After cleaning the spark plugs, check the spark plug gap "L" using a gap gauge. If it is not within the standard, replace the spark plug.
NOTE:
- Never use a plug cleaner.
- Do not use a metal brush as it may damage the electrode area.
Spark plug gap L: Standard 0.7 - 0.8 mm (0.028 - 0.031 in)
RENDER: 1.0x
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.