A leak-down test measures cylinder sealing by pressurizing each cylinder with compressed air and measuring pressure loss, helping diagnose piston ring wear, valve sealing issues, and head gasket leaks.

Warnings

Tools required

Parts

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

Preparation

1. Ensure engine is completely cold (at least 2 hours after last operation)
2. Park vehicle on level surface, engage parking brake, and place transmission in Park
3. Open hood and secure in raised position
4. Disconnect negative battery terminal to prevent accidental starter engagement
5. Verify compressed air supply provides consistent 90-100 psi pressure
6. Calibrate leak-down tester according to manufacturer instructions (typically 10-15% leakage is acceptable baseline)

Procedure

1. 1

   Remove engine cover and ignition coils
   Remove the plastic engine cover by pulling upward on the clips. Disconnect all four ignition coil electrical connectors by pressing the release tab and pulling straight up. Remove the 10mm bolts securing each ignition coil (one per coil) and extract coils from spark plug tubes. Keep coils organized by cylinder number.
2. 2

   Remove all spark plugs
   Using the spark plug socket and extension, carefully remove all four spark plugs. Inspect threads and electrodes for damage or excessive wear. Store plugs in order (cylinders 1-4 from front to back). Clean any debris from spark plug wells using compressed air before proceeding.
3. 3

   Remove oil filler cap and PCV connections
   Remove the engine oil filler cap to prevent pressure buildup during testing. Disconnect the PCV valve hose if accessible to allow air to escape from the crankcase during the test. This helps identify if leakage is bypassing the rings into the crankcase.
4. 4

   Position cylinder 1 at TDC compression stroke
   Using a breaker bar on the crankshaft pulley bolt (24mm), rotate the engine clockwise (viewed from front) until cylinder 1 is at top dead center on the compression stroke. Confirm both intake and exhaust valves are closed by observing valve movement through the spark plug hole with a flashlight or using a piston position indicator. The piston should be at its highest point in the bore.
   ⚠Only rotate engine in normal rotation direction (clockwise from front). Never rotate backward as this can damage timing chain tensioner.
5. 5

   Perform leak-down test on cylinder 1
   Thread the leak-down tester adapter into cylinder 1 spark plug hole hand-tight, then snug with a wrench. Connect the compressed air supply to the tester. Slowly pressurize the cylinder to 90-100 psi while monitoring both gauges. Record the percentage of leakage shown on the gauge. Normal leakage is 5-10%, marginal is 10-20%, and excessive is above 20%. Listen at the throttle body (intake valve leak), exhaust pipe (exhaust valve leak), oil filler (ring leak), and radiator (head gasket leak) to identify leak source.
6. 6

   Test cylinder 2
   Release air pressure and remove tester from cylinder 1. Rotate crankshaft 180 degrees clockwise to position cylinder 2 at TDC compression stroke (confirm valves closed). Install leak-down tester and repeat test procedure. Record leakage percentage and identify any leak sources by listening at key locations.
7. 7

   Test cylinder 3
   Release air pressure and remove tester from cylinder 2. Rotate crankshaft another 180 degrees clockwise to position cylinder 3 at TDC compression stroke. Install leak-down tester and perform test. Record results and note any abnormal leak sources. The firing order is 1-3-4-2, so cylinder 3 follows cylinder 2 in the test sequence.
8. 8

   Test cylinder 4
   Release air pressure and remove tester from cylinder 3. Rotate crankshaft 180 degrees clockwise to position cylinder 4 at TDC compression stroke. Install leak-down tester and complete final cylinder test. Record leakage percentage and identify leak sources. Compare all four cylinders for consistency.
9. 9

   Analyze test results
   Review all four cylinder leakage percentages. Consistent readings of 5-10% indicate good engine condition. Readings of 10-20% suggest normal wear. Above 20% indicates problems requiring attention. If one cylinder shows significantly higher leakage than others (more than 10% difference), investigate that specific cylinder. Air heard at throttle body indicates intake valve issues, at exhaust indicates exhaust valve problems, at oil filler indicates ring wear, and at radiator indicates head gasket failure.
10. 10

    Reinstall spark plugs
    Apply a small amount of anti-seize compound to spark plug threads (avoid electrode area). Install all four spark plugs hand-tight, then torque to specification using spark plug socket. For this engine, torque spark plugs to 18 Nm (13 lb-ft) if new, or 13 Nm (10 lb-ft) if reusing existing plugs in good condition.
11. 11

    Reinstall ignition coils
    Apply dielectric grease to inside of ignition coil boots. Install coils into spark plug tubes ensuring they seat fully on the plugs. Install the 10mm mounting bolts for each coil. Reconnect all four ignition coil electrical connectors ensuring they click securely into place.
12. 12

    Reinstall components and reconnect battery
    Reinstall PCV hose if disconnected. Install engine oil filler cap securely. Reinstall plastic engine cover by aligning clips and pressing firmly until seated. Reconnect negative battery terminal. Clear any diagnostic trouble codes that may have been stored during testing.

Reassembly

1. Ensure all four ignition coil connectors are securely fastened and clicked into place
2. Verify engine oil filler cap is tight to prevent oil leaks and maintain crankcase pressure
3. Confirm all tools and equipment are removed from engine bay before starting vehicle
4. Document all leak-down percentages and leak sources for maintenance records

Verification

• Start engine and verify smooth idle with no misfires (may run rough for first few seconds as fuel system reprimes)
• Check for proper ignition coil seating by listening for arcing sounds or observing misfire codes
• Compare leak-down test results to acceptable ranges: 5-10% excellent, 10-20% acceptable with monitoring, above 20% requires repair
• If excessive leakage was found, correlate with other symptoms such as oil consumption, rough idle, or loss of power to determine repair priority
• Retest after any repairs to verify improvement in cylinder sealing

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