Cummins/Onan — Servicing Pulsating Diaphragm Fuel Pump
Maintenance
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Before you start
- A clogged diaphragm air bleed hole can cause diaphragm wear and seal damage while inhibiting pump operation.
- Use care when reassembling and reinstalling the pump. Improper parts alignment or misconnected fuel lines may result in leaking fuel, creating a serious fire hazard.
Procedure
- Remove vacuum and fuel lines; inspect lines for wear or cracking.
- Scribe two lines across pump parts for correct alignment.
- Remove fuel pump attaching screws.
- Carefully pull sections of pump apart; diaphragm, plunger, return spring, plate, pump body, and gaskets will be loose.
- Check parts for wear and damage; replace with new parts as necessary.
- Ensure air bleed hole in pump base is unclogged.
- Replace gaskets and reassemble pump as shown in figure.
- Install pump and replace lines; make sure fuel line clamps are replaced.
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.