A leak-down test measures cylinder sealing efficiency by pressurizing each cylinder with compressed air and measuring pressure loss, helping diagnose worn piston rings, valve seating issues, or head gasket failures.

Warnings

Tools required

Parts

• Spark plugs (if replacement needed) × 4 — 90919-01253 or equivalent

Preparation

1. Ensure engine is completely cold to touch
2. Park vehicle on level surface, engage parking brake, and place transmission in Park
3. Disconnect battery negative terminal and wait 90 seconds for airbag system to discharge
4. Remove engine cover by pulling upward on four corners to release clips
5. Label and photograph ignition coil connections for proper reinstallation

Procedure

1. 1

   Remove ignition coils
   Disconnect the electrical connector from each ignition coil by pressing the tab and pulling straight up. Remove the 10mm bolt securing each coil. Use a twisting and pulling motion to extract each coil from the spark plug well. Keep coils in order (Cylinder 1 is on timing belt end, Cylinder 4 is on transmission end).
2. 2

   Remove all spark plugs
   Using a spark plug socket with extension, remove all four spark plugs. Inspect plugs for oil fouling, carbon deposits, or damage. Keep plugs in order by cylinder number for diagnostic reference. Check spark plug wells for oil accumulation which may indicate valve cover gasket issues.
3. 3

   Position cylinder 1 at TDC compression stroke
   Rotate the crankshaft clockwise using a 19mm socket on the crankshaft pulley bolt until cylinder 1 is at top dead center on the compression stroke. Verify both intake and exhaust valves are closed by checking valve movement through the spark plug hole. You can feel compression building if you place your thumb over the spark plug hole while rotating the engine.
4. 4

   Install leak-down tester on cylinder 1
   Thread the leak-down tester adapter into cylinder 1 spark plug hole hand-tight, then snug with a wrench. Do not over-tighten. Connect the leak-down tester to the adapter and to the compressed air supply. Set regulator to 100 PSI input pressure per tester manufacturer specifications.
5. 5

   Perform leak-down test on cylinder 1
   With piston at TDC, slowly apply compressed air while holding the crankshaft to prevent rotation. Allow pressure to stabilize for 5-10 seconds, then record both input and output gauge readings. Calculate leak-down percentage: ((Input PSI - Output PSI) / Input PSI) × 100. Listen at tailpipe for exhaust valve leaks, intake for intake valve leaks, oil filler cap for ring leaks, and radiator for head gasket leaks. Record all findings.
6. 6

   Test cylinder 2
   Release air pressure and remove tester. Rotate crankshaft 180 degrees clockwise to position cylinder 2 at TDC compression stroke (verify both valves closed). Install leak-down tester and repeat test procedure. Record readings and listen for air leakage locations.
7. 7

   Test cylinder 3
   Release air pressure and remove tester. Rotate crankshaft another 180 degrees clockwise to position cylinder 3 at TDC compression stroke. Install leak-down tester and repeat test procedure. Record readings and listen for air leakage locations.
8. 8

   Test cylinder 4
   Release air pressure and remove tester. Rotate crankshaft final 180 degrees clockwise to position cylinder 4 at TDC compression stroke. Install leak-down tester and repeat test procedure. Record readings and listen for air leakage locations.
9. 9

   Analyze test results
   Compare leak-down percentages across all cylinders. Normal range is 5-10%, acceptable up to 15%. Values above 20% indicate significant problems. Air hissing from tailpipe indicates exhaust valve leakage. Air from intake indicates intake valve leakage. Air from oil filler cap indicates piston ring or cylinder wall wear. Air bubbling in coolant indicates head gasket failure. Variation greater than 10% between cylinders suggests uneven wear.
10. 10

    Reinstall spark plugs
    Inspect spark plug threads and clean any debris from wells. Install spark plugs hand-tight first, then torque to manufacturer specification (typically 18-22 Nm for this engine, though not in provided torque list - use factory service manual specification). Ensure plugs are properly gapped if reusing or installing new plugs.
11. 11

    Reinstall ignition coils
    Apply a thin coat of dielectric grease to inside of coil boots. Insert each coil into its respective cylinder spark plug well with a twisting motion to seat properly. Install and tighten the 10mm mounting bolt on each coil. Reconnect electrical connectors ensuring they click into place.
12. 12

    Reinstall engine cover and reconnect battery
    Position engine cover and press firmly at all four corners until clips engage with audible clicks. Reconnect battery negative terminal. Clear any diagnostic codes that may have been set from disconnecting battery or sensors.

Reassembly

1. Verify all ignition coil electrical connectors are fully seated and locked
2. Confirm engine cover is securely clipped at all four mounting points
3. Battery negative terminal must be tight to prevent starting or electrical issues

Verification

• Start engine and verify smooth idle with no misfires or rough running
• Check for any diagnostic trouble codes related to ignition system
• Verify leak-down test results are documented with percentages for each cylinder and location of any air leakage
• If leak-down exceeds 20% on any cylinder, further diagnosis is required (compression test, borescope inspection, or teardown)
• Compare results between cylinders - variations greater than 10% indicate uneven wear patterns

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