Cummins/Onan 3.6MKY / 4MKY — Fuel Pump Test
Testing & diagnosis
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
- Do not substitute an automotive electric fuel pump for the Onan-supplied pump.
Procedure
- Make sure the fuel tank has sufficient fuel.
- Check battery voltage between the brown lead and ground when cranking and running (must exceed 6 VDC).
- Remove the fuel line from the carburetor inlet and install a pressure gauge.
- Press the Start switch and hold several seconds until pressure stabilizes.
- Reading should be 3.25-4.00 psi (22.4-27.5 kPa) and hold constant or drop slowly.
- If below 3.25 psi, tap the pump body to free the piston; replace pump if still faulty.
Tools required
- Pressure gauge Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 3.25-4.00 psi (22.4-27.5 kPa) outlet
- inlet minus 1.3 to positive 1.5 psi
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.