Cummins/Onan — Fuel Pump Pressure Test (Carburetor Models)
Testing & diagnosis · Fuel system
From a Cummins/Onan service manual — check it applies to your exact model before use.
Applies to: Cummins/Onan HGJAA, Cummins/Onan HGJAB, Cummins/Onan HGJAD, Cummins/Onan HGJAE
Before you start
- Do not substitute an automotive electric fuel pump; higher pressure can cause carburetor flooding or fuel leakage, creating a fire hazard.
Procedure
- Disconnect fuel line at the carburetor; connect a fuel pressure gauge reading 2.5 to 4 psi (17 to 27 kPa).
- Prime the system while observing the gauge.
- Pressure should hold constant 2.5 to 4 psi or drop off very slowly.
- If no response, replace the fuel pump (and fuel filter) with Cummins-supplied parts.
- If out of range, check inlet pressure (-1.3 to 1.5 psi).
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
- Outlet pressure 2.5 to 4 psi (17 to 27 kPa)
- Inlet pressure -1.3 to 1.5 psi
Full service-parts list: Cummins/Onan HGJAA →, Cummins/Onan HGJAB →, Cummins/Onan HGJAD →
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.