This procedure tests the compression pressure in each cylinder of the 2.5L I4 engine to diagnose engine mechanical condition and identify potential issues with valves, rings, or head gasket.

Warnings

Tools required

Parts

• Spark plugs (if damaged during removal) × 4 — 90919-01253 or equivalent NGK/Denso

Preparation

1. Ensure engine is at normal operating temperature (176-203°F coolant temperature)
2. Park vehicle on level surface and engage parking brake
3. Turn ignition off and remove key
4. Allow engine to cool for 10-15 minutes to avoid burns while remaining warm
5. Open hood and secure with prop rod
6. Gather all tools and compression testing equipment

Procedure

1. 1

   Disable fuel and ignition systems
   Locate the engine room fuse box on the driver's side of the engine bay. Remove the EFI MAIN fuse (25A) to disable fuel injection. Remove the IGN fuse (10A) to disable the ignition system. This prevents fuel delivery and spark during compression testing.
2. 2

   Remove ignition coils and connectors
   Disconnect the four ignition coil electrical connectors by pressing the release tabs. Remove each ignition coil by loosening the mounting bolt and pulling the coil straight up from the spark plug well. Label coils 1-4 from left to right (timing belt end is cylinder 1) to ensure correct reinstallation.
   Torque spec

   Mounting Bolts27 Nm (20 lb-ft)
3. 3

   Remove all four spark plugs
   Using a 16mm spark plug socket with extension, remove all four spark plugs. Turn counterclockwise to loosen. Inspect spark plugs for fouling, oil deposits, or damage. Keep spark plugs in order by cylinder number for diagnostic reference. Check spark plug gaps if reusing (0.043 inches/1.1mm).
   ⚠Spark plug wells may contain debris. Clean wells with compressed air before removing plugs to prevent debris from entering cylinders.
4. 4

   Install compression gauge in cylinder 1
   Thread the compression gauge adapter hand-tight into cylinder 1 spark plug hole (left-most cylinder). Ensure gauge is fully seated and connection is secure to prevent pressure leaks. Do not over-tighten the gauge adapter.
5. 5

   Crank engine and record cylinder 1 pressure
   Fully depress the accelerator pedal to open the throttle plate. Have an assistant crank the engine for 5-6 compression strokes (approximately 3-4 seconds) or use a remote starter switch. Observe the compression gauge and record the maximum pressure reached. Normal compression is 185-200 psi.
   ⚠Do not crank engine for more than 5 seconds continuously. Allow starter motor to cool for 30 seconds between cranking cycles.
6. 6

   Test remaining cylinders
   Release pressure from compression gauge. Remove gauge from cylinder 1 and install in cylinder 2. Repeat cranking procedure and record pressure. Continue this process for cylinders 3 and 4, recording each result. Compare all readings to ensure variation does not exceed 14 psi between any cylinders.
7. 7

   Analyze compression results
   Review all four cylinder compression readings. Normal range is 185-200 psi with maximum 14 psi variation. Low compression in one cylinder may indicate burnt valve, broken rings, or head gasket leak. Low compression in adjacent cylinders suggests head gasket failure. Low compression in all cylinders indicates worn rings or incorrect valve timing.
8. 8

   Perform wet test if compression is low
   If any cylinder reads below 170 psi, perform a wet compression test. Add approximately 1 tablespoon (15ml) of clean engine oil through the spark plug hole into the low cylinder. Reinstall compression gauge and retest. If compression increases significantly (30+ psi), rings are worn. If compression remains the same, valve or head gasket issue is indicated.
9. 9

   Reinstall spark plugs
   Inspect spark plug threads and insulators. Apply a small amount of anti-seize compound to spark plug threads (avoid electrode area). Install each spark plug hand-tight into the correct cylinder, then torque to 18 Nm (13 lb-ft) using a torque wrench. Do not over-torque as this can damage aluminum cylinder head threads.
   ⚠Cross-threading spark plugs in aluminum heads can cause expensive damage. Always start threading by hand and ensure plugs turn smoothly.
10. 10

    Reinstall ignition coils
    Apply dielectric grease to inside of ignition coil boots if desired. Install each ignition coil onto its corresponding spark plug, ensuring proper seating. Install and torque mounting bolts. Reconnect electrical connectors to each coil, ensuring they click into place securely.
    Torque spec

    Mounting Bolts27 Nm (20 lb-ft)
11. 11

    Restore fuel and ignition systems
    Reinstall the IGN fuse (10A) and EFI MAIN fuse (25A) in the engine room fuse box. Verify all fuses are fully seated. Close fuse box cover.

Reassembly

1. Verify all ignition coil electrical connectors are properly secured
2. Confirm all tools and equipment have been removed from engine bay
3. Check that no spark plug wires or hoses were disturbed during procedure

Verification

• Start engine and verify it runs smoothly without misfires
• Check for diagnostic trouble codes using OBD-II scanner
• Listen for any unusual noises that might indicate improper spark plug installation
• Verify compression readings are documented: all cylinders should be 185-200 psi with less than 14 psi variation
• If compression was low, recommend further diagnosis or cylinder leak-down test to pinpoint exact failure location

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