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Home›Repair guides›Cummins/Onan›Engine Cylinder Compression Check

Cummins/Onan GTA14 / GTA14 qi 20 NA — Engine Cylinder Compression Check

Testing & diagnosis · Engine cylinders

For the Cummins/Onan GTA14 / GTA14 qi 20 NA, from the Cummins/Onan owner's manual.

Applies to: Cummins/Onan GTA14 qi 20 NA, Cummins/Onan GTA14 engine

Before you start

  • Verify batteries have full charge before starting

Procedure

  1. Shut off gas fuel valve and tag DO NOT OPEN.
  2. Ground the ignition G lead to prevent ignition spark.
  3. Remove spark plug probes and check for oil or water contamination.
  4. Remove spark plugs from all cylinders.
  5. Block engine throttle wide open.
  6. Install compression gauge in #1 cylinder.
  7. Crank engine until 6 to 8 revolutions and gauge reading is stable.
  8. Record reading in psi.
  9. Release gauge pressure and remove gauge.
  10. Repeat for each cylinder.

Tools required

Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.

Specs & values

  • All cylinder pressures should be within a 10 percent variance

Full service-parts list: Cummins/Onan GTA14 qi 20 NA →

Source: Cummins/Onan owner's 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.

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