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

Warnings

Tools required

Parts

• Spark plug anti-seize compound × 1 — Use OEM specification
• Shop towels × 1 — Generic

Preparation

1. Ensure engine is completely cold (not run for at least 2 hours)
2. Park vehicle on level surface and engage parking brake
3. Verify you have a reliable compressed air source capable of maintaining 80-100 PSI
4. Gather leak-down tester, notepad, and recording materials
5. Open hood and ensure adequate lighting and workspace
6. Disconnect negative battery terminal to disable ignition system

Procedure

1. 1

   Remove engine cover and ignition coils
   Remove the plastic engine cover by lifting upward (press tabs if present). Disconnect all four ignition coil electrical connectors by pressing the release tab and pulling straight up. Remove the mounting bolt from each coil using a 10mm socket, then pull coils straight out of spark plug wells. Label or photograph coil positions for reinstallation.
   Torque spec

   Mounting Bolts27 Nm (20 lb-ft)
2. 2

   Remove all spark plugs
   Use a 5/8" or 16mm spark plug socket to remove all four spark plugs. Turn counterclockwise to loosen. Keep spark plugs in order by cylinder position (1-4, front to rear) for inspection. Inspect plugs for fouling, oil, or abnormal wear patterns which may correlate with leak-down results.
3. 3

   Prepare leak-down tester
   Connect the leak-down tester to your compressed air source. Calibrate the tester according to manufacturer instructions, typically by blocking the outlet hose completely and adjusting the regulator until both gauges read the same (usually 100 PSI input). Verify calibration is accurate before proceeding.
4. 4

   Position cylinder 1 at TDC compression stroke
   Insert the leak-down tester adapter into cylinder 1 spark plug hole (front cylinder). Rotate the crankshaft clockwise using a breaker bar on the crankshaft pulley bolt (22mm socket) until cylinder 1 is at top dead center on compression stroke. Both intake and exhaust valves should be closed. You can verify by feeling resistance when trying to push a wooden dowel into the cylinder - piston should be at its highest point.
5. 5

   Test cylinder 1 leak-down
   Thread the leak-down tester hose adapter firmly into cylinder 1 spark plug hole. Apply compressed air slowly while holding the crankshaft to prevent rotation. Once pressurized (typically 100 PSI input), read the output gauge which shows percentage of leakage. Record the percentage. Listen at the intake, exhaust, oil filler cap, and adjacent cylinders to identify leak source: intake (intake valve), exhaust (exhaust valve), oil filler (rings), adjacent cylinder (head gasket). Document all findings.
6. 6

   Test cylinder 2 leak-down
   Remove tester from cylinder 1. Rotate crankshaft approximately 180 degrees clockwise to position cylinder 2 at TDC compression stroke (second from front). Verify both valves are closed. Install leak-down tester adapter into cylinder 2 spark plug hole. Apply air pressure and record leakage percentage and leak source location. Document results.
7. 7

   Test cylinder 3 leak-down
   Remove tester from cylinder 2. Rotate crankshaft approximately 180 degrees clockwise to position cylinder 3 at TDC compression stroke (second from rear). Verify both valves are closed. Install leak-down tester adapter into cylinder 3 spark plug hole. Apply air pressure and record leakage percentage and leak source location. Document results.
8. 8

   Test cylinder 4 leak-down
   Remove tester from cylinder 3. Rotate crankshaft approximately 180 degrees clockwise to position cylinder 4 at TDC compression stroke (rear cylinder). Verify both valves are closed. Install leak-down tester adapter into cylinder 4 spark plug hole. Apply air pressure and record leakage percentage and leak source location. Document results.
9. 9

   Analyze results and document findings
   Compare all four cylinder readings. Normal leak-down for this 2AR-FE engine is 5-10%. Results between 10-15% suggest minor wear but may be acceptable. Results over 15-20% indicate significant issues requiring repair. If one cylinder differs significantly from others, focus diagnosis on that cylinder. Document whether leakage is from valves (intake/exhaust noise), rings (oil filler/crankcase), or head gasket (adjacent cylinder/coolant).
10. 10

    Reinstall spark plugs
    Apply a small amount of anti-seize compound to spark plug threads (avoid getting compound on electrode). Install all four spark plugs hand-tight first, then torque to specification. For this engine, spark plugs should be torqued to 18 Nm (13 lb-ft) - use a torque wrench as over-tightening can damage aluminum threads.
11. 11

    Reinstall ignition coils
    Insert each ignition coil back into its corresponding spark plug well, ensuring proper seating. Install the mounting bolt on each coil and torque to specification. Reconnect all four ignition coil electrical connectors, ensuring they click into place securely.
    Torque spec

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

    Reconnect battery and reinstall engine cover
    Reconnect the negative battery terminal. Reinstall the plastic engine cover by aligning mounting points and pressing down until clips engage. Ensure cover is fully seated and secure.

Reassembly

1. Ensure all spark plugs are torqued properly to avoid damage to aluminum cylinder head threads
2. Verify all ignition coil connectors are fully seated and clicked into place
3. Double-check that engine cover is properly installed and all clips are engaged

Verification

• Compare leak-down percentages across all four cylinders - readings should be relatively consistent (within 5% of each other)
• Review documented leak sources to determine root cause of any excessive leakage
• Start engine and verify smooth idle with no misfires - reconnect scan tool if necessary to check for codes
• Normal results (under 10% leakage) indicate good cylinder sealing with no immediate action required
• If any cylinder shows over 15-20% leakage, further diagnosis is required (borescope inspection, compression test, or disassembly)

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