A leak-down test measures cylinder sealing by pressurizing each cylinder with compressed air and measuring how much air escapes, helping diagnose piston ring wear, valve seat damage, or head gasket leaks.

Warnings

Tools required

Parts

• Spark plug gasket/washer set (if original gaskets damaged) × 1 — 90080-17127 or equivalent

Preparation

1. Park vehicle on level surface and engage parking brake
2. Allow engine to reach normal operating temperature, then shut off and cool for 30 minutes (warm but safe to touch)
3. Disconnect negative battery terminal to prevent accidental starting
4. Remove engine cover by pulling upward on cover to release clips
5. Set up compressed air source and regulate to 80-100 PSI as specified by leak-down tester manufacturer
6. Prepare notepad with chart to record cylinder number, leak-down percentage, and location of air escape for all four cylinders
7. Ensure you have access to crankshaft pulley bolt to rotate engine manually

Procedure

1. 1

   Remove ignition coils and spark plugs
   Disconnect all four ignition coil electrical connectors by pressing the release tab and pulling straight up. Remove the coil mounting bolts and pull coils straight out from spark plug wells. Using a 16mm spark plug socket, carefully remove all four spark plugs. Inspect spark plug condition and note any abnormalities. Keep plugs organized by cylinder number for reference.
2. 2

   Disable fuel system
   Remove the fuel pump relay or fuse from the engine bay fuse box to prevent fuel delivery during testing. This prevents fuel from washing cylinder walls during the test and potential hydrolock.
3. 3

   Bring cylinder 1 to TDC compression stroke
   Locate cylinder 1 (driver's side, closest to timing belt). Using a breaker bar on the crankshaft pulley bolt (22mm), rotate the engine clockwise (viewed from front) while observing cylinder 1 spark plug hole. Feel for air pressure escaping, indicating compression stroke. Continue rotating until piston is at the top of its travel. Verify TDC by checking that both intake and exhaust valves are closed (use a screwdriver or wire to confirm piston is at highest point).
4. 4

   Install leak-down tester on cylinder 1
   Thread the leak-down tester adapter into cylinder 1 spark plug hole, ensuring it seats properly. Do not over-tighten the adapter. Connect the leak-down tester assembly to the adapter and to the compressed air source. Ensure the tester air supply valve is closed before connecting air pressure.
   ⚠Confirm piston is exactly at TDC before applying air pressure. If piston is not at TDC, compressed air will force the engine to rotate violently.
5. 5

   Perform leak-down test on cylinder 1
   Slowly open the air supply valve on the leak-down tester to pressurize cylinder 1. Read both gauges: the input pressure and the percentage of leakage. A healthy cylinder should show 5% or less leakage; 10-15% is acceptable; above 20% indicates problems. Hold pressure for 10-15 seconds to get a stable reading. While pressurized, listen at the throttle body (intake valve leak), exhaust tailpipe (exhaust valve leak), oil filler cap (piston ring leak), and coolant reservoir (head gasket leak) to identify the source of air escape. Record percentage and leak location.
6. 6

   Release pressure and move to cylinder 2
   Close the air supply valve and disconnect the leak-down tester from cylinder 1. Rotate the crankshaft 180 degrees clockwise (half revolution) to bring cylinder 2 to TDC compression stroke. Cylinder firing order is 1-3-4-2, so the next cylinder in compression sequence is cylinder 3, but for systematic testing, proceed sequentially. Rotate crankshaft approximately 540 degrees (1.5 revolutions) clockwise from cylinder 1 TDC to reach cylinder 2 TDC compression stroke. Verify both valves are closed.
7. 7

   Test cylinder 2
   Install leak-down tester adapter in cylinder 2 (second from driver's side). Repeat the pressurization and leak detection procedure as performed on cylinder 1. Record leak-down percentage and source of any air escape. Compare results to cylinder 1.
8. 8

   Test cylinder 3
   Release pressure and rotate crankshaft to bring cylinder 3 (second from passenger side) to TDC compression stroke. Install leak-down tester and perform test. Record results. Note any significant variation between cylinders, as consistent readings across all cylinders can indicate normal wear, while one outlier suggests a specific problem.
9. 9

   Test cylinder 4
   Release pressure and rotate crankshaft to bring cylinder 4 (passenger side, closest to firewall) to TDC compression stroke. Install leak-down tester and perform final test. Record results and compare all four cylinders.
10. 10

    Analyze results and identify issues
    Review all recorded data. Leakage interpretation: 0-5% = excellent condition; 5-10% = good condition; 10-20% = marginal, monitor; 20-30% = repair needed soon; above 30% = immediate repair required. Identify leak sources: hissing from throttle body indicates intake valve not sealing; hissing from tailpipe indicates exhaust valve issues; bubbling in coolant reservoir indicates head gasket or cracked head; air from oil filler or dipstick tube indicates worn piston rings or cylinder wall damage. Note that adjacent cylinders with similar high leakage may indicate head gasket failure between them.
11. 11

    Reinstall spark plugs
    Inspect spark plug threads and cylinder head threads for damage. Install spark plugs by hand first to ensure proper thread engagement, then tighten to manufacturer specification using torque wrench. Note: Spark plug torque is not provided in database; follow spark plug manufacturer specification typically 18-22 Nm (13-16 lb-ft) for this engine with gasket seat plugs.
12. 12

    Reinstall ignition coils
    Place ignition coils back into spark plug wells, ensuring they seat fully onto spark plugs. Install coil mounting bolts and tighten. Reconnect all four ignition coil electrical connectors until they click into place.
13. 13

    Restore fuel system and battery
    Reinstall fuel pump relay or fuse to restore fuel system operation. Reconnect negative battery terminal. Reinstall engine cover by aligning clips and pressing down firmly until cover clicks into place.

Reassembly

1. Ensure all ignition coil connectors are fully seated and locked
2. Verify engine cover is properly secured with all clips engaged
3. Double-check that all tools and test equipment are removed from engine bay
4. Confirm battery is reconnected and terminals are clean and tight

Verification

• Start engine and verify it runs smoothly without misfires (may run rough for first few seconds as fuel system reprimes)
• Check for any abnormal noises or vibrations that weren't present before testing
• Verify no check engine lights or codes related to ignition system
• Review leak-down test results: acceptable readings are below 15% leakage per cylinder with no more than 5% variation between cylinders
• If leak-down results show problems, use the leak source identification to determine next repair steps (valve job, ring replacement, head gasket, etc.)
• Document all test results in vehicle maintenance records for future reference and trending

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