A leak-down test measures the percentage of air leakage past the piston rings, valves, and head gasket to diagnose internal engine condition without disassembly.

Warnings

Tools required

Parts

• Spark plugs (if fouled or damaged during removal) × 4 — Use OEM specification

Preparation

1. Ensure engine is completely cold (not run for at least 2 hours)
2. Park vehicle on level surface, engage parking brake, and place transmission in Park
3. Verify compressed air supply can maintain 90-100 PSI with regulator set properly
4. Locate Top Dead Center (TDC) marks on crankshaft pulley and timing cover for reference
5. Prepare notebook to record leak-down percentages and observations for all four cylinders

Procedure

1. 1

   Remove engine cover and air intake system
   Remove the plastic engine cover by pulling upward on retention clips. Disconnect the air intake tube from the throttle body. Release clips securing the air box and remove the entire air intake assembly to access the ignition coils.
   Torque spec

   Air Box Clips5 Nm (4 lb-ft)
2. 2

   Remove ignition coils
   Disconnect electrical connectors from all four ignition coils by pressing release tabs. Remove the mounting bolts securing each coil (typically 10mm). Carefully pull each coil straight up out of the spark plug wells. Inspect coils for oil contamination which would indicate valve cover gasket issues.
   Torque spec

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

   Remove all spark plugs
   Using a spark plug socket (typically 14mm or 16mm for this engine), remove all four spark plugs. Keep them in order if evaluating plug condition. Inspect plug threads and apply anti-seize to new or reinstalled plugs. Removing all plugs allows the engine to rotate freely and prevents pressure buildup in adjacent cylinders.
   ⚠Do not drop debris into spark plug wells - cover open cylinders with clean shop towels when not testing
4. 4

   Rotate engine to TDC for cylinder 1
   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. Both intake and exhaust valves should be fully closed. Verify position by checking timing marks on crankshaft pulley align with TDC indicator on timing cover. You can also insert a long screwdriver into cylinder 1 spark plug hole to feel piston position.
   ℹ️Firing order is 1-3-4-2, use this to sequence testing efficiently
5. 5

   Install leak-down tester in cylinder 1
   Thread the leak-down tester adapter hand-tight into cylinder 1 spark plug hole. Connect the air supply hose to the tester. Set the regulator to deliver exactly 100 PSI to the cylinder gauge (reference gauge on tester). Some testers require pressurizing to 100 PSI input before connecting to cylinder.
   ⚠If piston is not exactly at TDC, air pressure will rotate the engine - ensure proper TDC positioning first
6. 6

   Perform leak-down test on cylinder 1
   Slowly apply air pressure while monitoring both gauges on the leak-down tester. The input gauge should read 100 PSI. The cylinder gauge shows actual pressure retained. Calculate leak-down percentage: (100 - cylinder pressure) = leak-down %. For example, if cylinder holds 85 PSI, leak-down is 15%. Acceptable is typically under 10%, marginal is 10-20%, poor is over 20%. While pressurized, listen at tailpipe (exhaust valve leak), throttle body (intake valve leak), oil filler cap (ring blow-by), and radiator (head gasket leak). Record all findings.
   ℹ️Some air loss to crankcase (3-5%) is normal on any engine
7. 7

   Test remaining cylinders
   Release air pressure and remove tester from cylinder 1. Rotate crankshaft 180 degrees clockwise to bring cylinder 3 to TDC (next in firing order). Repeat leak-down test procedure. Continue with cylinder 4 (another 180 degrees), then cylinder 2 (final 180 degrees). Each cylinder should be tested at its compression TDC. Record all percentages and listening test results for comparison.
   ⚠Always verify valves are closed before applying air pressure to each cylinder
8. 8

   Analyze test results
   Compare leak-down percentages across all cylinders. Variation between cylinders should be minimal (within 5%). High leak-down in one cylinder indicates localized problem. High leak-down in adjacent cylinders may indicate head gasket failure between them. Consistent high leak-down in all cylinders suggests worn rings. Use listening test results to pinpoint source: hissing at intake = intake valve leak; hissing at exhaust = exhaust valve leak; hissing at oil cap = ring wear; bubbling in coolant = head gasket leak.
9. 9

   Reinstall spark plugs
   Inspect spark plug threads and apply small amount of anti-seize compound if desired (avoid getting on electrode). Thread each spark plug by hand first to prevent cross-threading. Tighten spark plugs to manufacturer specification (typically 15-20 lb-ft for this engine, though not specifically listed in provided torque specs - use service manual value). Install in same cylinder positions if reusing.
10. 10

    Reinstall ignition coils
    Insert each ignition coil fully into its spark plug well ensuring proper seating. Install mounting bolts and torque to specification. Reconnect electrical connectors to each coil until they click into place. Verify secure connection on all four coils.
    Torque spec

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

    Reinstall air intake system and engine cover
    Reinstall air box assembly and secure all clips. Reconnect air intake tube to throttle body ensuring clamp is tight. Reinstall engine cover by pressing down on retention clip locations until fully seated.
    Torque spec

    Air Box Clips5 Nm (4 lb-ft)

Reassembly

1. Double-check all electrical connections are fully seated and locked
2. Verify no tools or rags were left in engine bay
3. Ensure all spark plug wires or coil connectors are in correct firing order sequence

Verification

• Start engine and listen for smooth idle with no misfires indicating proper spark plug and coil installation
• Check for unusual noises or vibrations that might indicate loose components
• Compare leak-down test results to acceptable standards: under 10% is good, 10-20% is marginal and requires monitoring, over 20% indicates repair needed
• If leak-down was excessive in any cylinder, recommend further diagnosis or repair based on leak source identified during listening tests

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