Cummins/Onan B43 / B48 — Pulsating-Diaphragm 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.
Procedure
- Operate engine at idle for five minutes.
- Shut off and remove fuel inlet line.
- Connect vacuum gauge to pump inlet.
- Start engine, idle five seconds, record vacuum.
- Move throttle to high idle, wait five seconds, record vacuum.
- Shut off and reconnect fuel inlet line.
- Remove fuel outlet line and connect pressure gauge.
- Start engine, idle five seconds, record pressure.
- Move throttle to high idle, record pressure.
- Shut off and reconnect fuel outlet line.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Inlet vacuum minimum 2.6 inches Hg
- Outlet pressure minimum 1.7 psi
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.