Perform a compression test on all four cylinders of the 2.5L I4 engine to diagnose engine condition and identify potential issues with valves, rings, or head gasket.

Warnings

Tools required

Parts

• Spark plug gasket/seal set (if reusing plugs) × 1 — Use OEM specification

Preparation

1. Warm engine to full operating temperature (coolant temperature above 175°F) before beginning test
2. Park vehicle on level surface, apply parking brake, and place transmission in Park
3. Turn off engine and allow to sit for 2-3 minutes
4. Ensure battery is fully charged for consistent cranking speed during test
5. Gather all tools and compression gauge before starting

Procedure

1. 1

   Remove engine cover
   Grasp the plastic engine cover at both sides and pull upward firmly to disengage the four mounting grommets. Set cover aside.
2. 2

   Disconnect ignition coils
   Locate all four ignition coils on top of the valve cover. Press the locking tab on each coil electrical connector and pull straight up to disconnect. Label or keep track of cylinder positions 1-4 (1 is closest to timing belt/accessory drive end).
3. 3

   Remove ignition coils
   Remove the single 10mm bolt securing each ignition coil. Pull each coil straight up with a twisting motion to remove from spark plug well. Inspect coil boots for damage or oil contamination.
   Torque spec

   Mounting Bolts27 Nm (20 lb-ft)
4. 4

   Disable fuel system
   Locate the EFI fuse (typically 15A or 20A) in the engine compartment fuse box. Use fuse puller to remove the EFI fuse to disable fuel injector operation. This fuse may be labeled EFI MAIN or INJ in the fuse box diagram.
   ℹ️Disabling fuel prevents raw fuel from washing cylinder walls during cranking, which would give false readings.
5. 5

   Remove all spark plugs
   Using spark plug socket and extension, remove all four spark plugs. Turn counterclockwise to loosen and remove completely. Keep plugs in order by cylinder number for inspection. Inspect plug condition and gap while removed.
   ⚠Spark plug wells may contain oil or debris. Clean wells with compressed air before removing plugs to prevent contamination from falling into cylinders.
6. 6

   Prepare compression gauge
   Select the appropriate adapter for the compression gauge that threads into the spark plug hole. Ensure gauge is zeroed or properly calibrated. Thread adapter hand-tight into cylinder #1 spark plug hole.
7. 7

   Test cylinder #1 compression
   With gauge installed in cylinder #1, fully depress throttle pedal to open throttle plate completely. Have assistant crank engine for 5-6 compression strokes (approximately 3-4 seconds) while watching gauge. Record maximum pressure reading. Throttle must remain wide open during entire cranking period.
   ⚠Ensure transmission is in Park and parking brake is engaged before cranking. Keep hands clear of engine bay during cranking.
8. 8

   Test remaining cylinders
   Remove compression gauge from cylinder #1. Repeat testing procedure for cylinders #2, #3, and #4 in order. Ensure consistent cranking duration (5-6 compression strokes) for each cylinder. Record all readings.
9. 9

   Analyze compression results
   Compare all four cylinder readings. Normal compression should be 142-191 psi with no more than 14 psi variation between highest and lowest cylinders. If any cylinder is low, perform wet test by adding approximately 1 tablespoon of engine oil through spark plug hole and re-testing. Significant increase indicates worn rings; no change indicates valve or head gasket issue.
   ℹ️Adjacent cylinders with similarly low compression may indicate head gasket failure between those cylinders.
10. 10

    Reinstall spark plugs
    Apply small amount of anti-seize to spark plug threads (avoid electrode end). Thread each spark plug by hand into correct cylinder to prevent cross-threading. Tighten spark plugs to 18 lb-ft (approximately 25 Nm). If original plugs have accumulated mileage or show wear, consider replacement.
    ⚠Do not over-torque spark plugs in aluminum cylinder head. Hand-tighten first, then use torque wrench for final tightening.
11. 11

    Reinstall ignition coils
    Apply thin layer of dielectric grease to inside of each coil boot. Push each coil firmly into spark plug well until fully seated. Install and tighten the 10mm mounting bolt on each coil. Reconnect electrical connector to each coil until locking tab clicks.
    Torque spec

    Mounting Bolts27 Nm (20 lb-ft)
12. 12

    Restore fuel system and test
    Reinstall the EFI fuse removed in step 4. Reinstall engine cover by aligning grommets and pressing down firmly. Turn ignition to ON position (without starting) for 2-3 seconds to prime fuel system, then start engine. Check for normal operation and verify no misfires or warning lights.

Reassembly

1. Verify all ignition coil connectors are fully locked and secure
2. Confirm engine cover is properly seated on all mounting grommets
3. Double-check that EFI fuse has been reinstalled to restore fuel system operation

Verification

• Start engine and verify smooth idle with no misfires or rough running
• Confirm no check engine light or ignition-related DTCs are present
• Listen for any unusual noises that might indicate loose components
• Review compression test results: all cylinders should be within 142-191 psi range with maximum 14 psi variation between cylinders

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