Cummins/Onan 3.6MKY / 4MKY — Leak Down Test
Testing & diagnosis · Engine cylinder
For the Cummins/Onan 3.6MKY / 4MKY, from the Cummins/Onan service manual.
Applies to: Cummins/Onan 3.6MKY, Cummins/Onan 4MKY
Before you start
- Disconnect battery negative cable to prevent accidental starting
Procedure
- Start engine and warm up for ten minutes.
- Disconnect battery negative (-) cable and remove spark plug.
- Manually rotate engine to top dead center (TDC) on compression stroke.
- Connect tester to shop air and set calibration; secure fan wheel.
- Screw air fitting into spark plug hole; attach plug fitting to tester.
- Read percentage of cylinder leakdown.
- If leakage greater than 30 percent, listen for air leakage at check points listed in Table 9-1.
Tools required
- Leak down tester Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 0-10% excellent
- 10-20% normal
- 20-30 FridayParts $58.50% service limit
- greater than 30% may need major service
Source: Cummins/Onan service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.