Cummins/Onan 6.3 NHEL / 6.5 NH — Fuel Pump Test
Testing & diagnosis · Electric fuel pump
For the Cummins/Onan 6.3 NHEL / 6.5 NH, from the Cummins/Onan service manual.
Applies to: Cummins/Onan NHEL
Before you start
- Do not substitute automotive type electric fuel pumps for standard Onan supplied electric pumps; higher output pressure can cause carburetor flooding or fuel leakage, creating a fire hazard.
Procedure
- Remove the fuel line from the pump outlet and install a pressure gauge.
- Press the START switch and hold it for several seconds until pressure reading is constant.
- For a good pump the pressure should read 4 to 5 psi (27.5 to 34.4 kPa) for units built June 1986 and before.
- For units built June 1986 and after, pressure should read 3-1/2 to 5 psi (17.2 to 34.4 kPa); replace pump if below 3-1/2 psi.
- Pressure should stay constant or drop off very slowly.
- If pressure is at zero, stop engine cranking, check electrical connections, press START switch and recheck.
Tools required
- Fuel pressure gauge Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 4 to 5 psi (27.5 to 34.4 kPa) before June 1986
- 3-1/2 to 5 psi (17.2 to 34.4 kPa) June 1986 and after
Full service-parts list: Cummins/Onan NHEL →
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.