Cummins/Onan B43 / B48 — Fuel Pump Test
Testing & diagnosis
For the Cummins/Onan B43 / B48, from the Cummins/Onan service manual.
Applies to: Cummins/Onan B48
Before you start
- Ignition of fuel can result in severe personal injury or death. Thoroughly clean up any spilled fuel.
Procedure
- Operate engine at an idle for five minutes to ensure carburetor is full of fuel.
- Shut engine off and remove fuel inlet line from fuel pump.
- Connect a vacuum gauge to fuel pump inlet using a piece of fuel hose with clamps.
- Start engine and allow to idle for at least five seconds; record vacuum gauge reading.
- Move throttle control to high idle position, wait at least five seconds, record vacuum gauge reading.
- Shut engine off and remove vacuum gauge hose; reconnect fuel inlet line.
- Remove fuel outlet line from fuel pump.
- Connect a pressure gauge to fuel pump outlet using a piece of fuel hose with clamps.
- Start engine and idle at least five seconds; record pressure gauge reading holding gauge level with pump outlet.
- Move throttle to high idle and run at least five seconds; record pressure reading.
- Shut engine off and remove pressure gauge hose; reconnect fuel outlet line.
- Repair or replace the fuel pump if test readings are not within TABLE 1 values.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Pump inlet vacuum minimum 2.6 inches of mercury (low idle and high idle)
- Pump outlet pressure minimum 1.7 psi (low idle and high idle)
Full service-parts list: Cummins/Onan B48 →
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.