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 MANAGEMENTTUNE-UP AND ENGINE PERFORMANCE CHECKSCOMPRESSION CHECKTESTING AND INSPECTION
2012 Subaru Impreza WRX STI F4-2.5L DOHC Turbo
Compression Check: Testing and Inspection
2012 Subaru Impreza WRX STI F4-2.5L DOHC TurboSECTION Testing and Inspection
Compression
INSPECTION
CAUTION:
After warming-up, engine becomes very hot. Be careful not to burn yourself during measurement.
1) After warming-up the engine, turn the ignition switch to OFF.
2) Make sure that the battery is fully charged.
3) Remove the fuse of fuel pump from main fuse box.
4) Start the engine and run it until it stalls.
5) After the engine stalls, crank it for five more seconds.
6) Turn the ignition switch to OFF.
7) Remove all spark plugs.
8) Fully open the throttle valve.
9) Check the starter motor for satisfactory performance and operation.
10) Install the compression gauge to the spark plug hole.
NOTE:
When using a screw-in type compression gauge, the screw should be less than 18 mm (0.71 in) long.
11) Crank the engine by starter motor and read the value when the needle of the compression gauge becomes stable.
NOTE:
- Perform at least two measurements per cylinder, and make sure that the values are correct.
- If the compression pressure is out of standard, check or adjust the pistons, valves and cylinders.
Compression (fully open throttle):
Standard
981 - 1,177 kPa (10 - 12 kgf/cm2, 142 - 171 psi)
Difference between cylinders
49 kPa (0.5 kgf/cm2, 7 psi) or less
12) After inspection, install the related parts in the reverse order of removal.
INSPECTION
CAUTION:
After warming-up, engine becomes very hot. Be careful not to burn yourself during measurement.
1) After warming-up the engine, turn the ignition switch to OFF.
2) Make sure that the battery is fully charged.
3) Remove the fuse of fuel pump from main fuse box.
4) Start the engine and run it until it stalls.
5) After the engine stalls, crank it for five more seconds.
6) Turn the ignition switch to OFF.
7) Remove all spark plugs.
8) Fully open the throttle valve.
9) Check the starter motor for satisfactory performance and operation.
10) Install the compression gauge to the spark plug hole.
NOTE:
When using a screw-in type compression gauge, the screw should be less than 18 mm (0.71 in) long.
11) Crank the engine by starter motor and read the value when the needle of the compression gauge becomes stable.
NOTE:
- Perform at least two measurements per cylinder, and make sure that the values are correct.
- If the compression pressure is out of standard, check or adjust the pistons, valves and cylinders.
Compression (fully open throttle):
Standard
981 - 1,177 kPa (10 - 12 kgf/cm2, 142 - 171 psi)
Difference between cylinders
49 kPa (0.5 kgf/cm2, 7 psi) or less
12) After inspection, install the related parts in the reverse order of removal.
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.