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Engine Leak Down Testing

Engine Leak Down Testing. “Engine performance taking a leak?”. Presentation of Symptoms. Symptoms are the same as those that would lead to a compression test Leak down is a more sophisticated test May be used as a pinpoint test after compression is checked.

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Engine Leak Down Testing

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  1. Engine Leak Down Testing “Engine performance taking a leak?”

  2. Presentation of Symptoms • Symptoms are the same as those that would lead to a compression test • Leak down is a more sophisticated test • May be used as a pinpoint test after compression is checked. • May technicians skip the compression test and go right to the leak down test. • Leak down testing equipment is more expensive, generally found only in vocational applications

  3. Advantages of Leak Down Testing • Can determine the exact cause of pressure loss • Valve leaks • Gasket leaks • Ring Leaks • Is almost as quick to setup as a compression test

  4. Test Setup • Starts the same as compression test • Disable ignition • Key off, remote start switch • Clear flood mode • Double check • Ignition disabled • Not in gear • Disconnect plug wires • Loosen sparkplugs 1 turn • Crank engine to clear debris • Remove spark plugs

  5. Gauge Calibration • Hook tester to shop air • Hook testing hose to tester • Turn regulator clockwise until the need reads 100% • Remove test hose • Gauge is now calibrated

  6. Engine Preparation • Thread hose into cylinder to be tested • Plug hose end with thumb • Crank engine until compression is felt from hose end • Continue to crank engine until compression stops • The engine is now at T.D.C. on the compression stroke. • Valves are closed • Piston will travel to B.D.C. when pressure is applied

  7. Test Procedure • Connect hose to tester • Air pressure will cause piston to travel to B.D.C. • If problems are encountered, bump starter to encourage piston movement • When gauge stabilizes, record reading. • Any reading in excess of 10% cylinder leakage is unacceptable • After all readings are recorded, compare to look for weak cylinders • If in doubt, test again

  8. Differential Diagnosis • Intake Valve • If air is leaking out the intake valve, it will be heard from the carburetor or throttle body • Exhaust Valve • If air is leaking out the exhaust valve, it will be heard from the exhaust pipe • Rings • If air is leaking past the rings, it will be heard coming from the oil fill hole • Head Gasket • If air is leaking through the head gasket, bubbles may appear in the coolant in the radiator

  9. Confirming a Diagnosis • Keep in mind that a diagnosis is only a guess until you find the smoking gun • To verify the diagnosis, additional inspections will be necessary • In the case of cylinder seal problems, these inspections are labor intensive • Going further takes you past the point of no return – its going to be expensive no matter what • Check with the customer before proceeding

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