Cummins/Onan — Electric Fuel Pump Service
Repair & overhaul
From a Cummins/Onan service manual covering: 2.5 MAJB-53BR, 2.5 MAJB-53CR, 3.0 MAJB-1R. Check it applies to your exact model before use.
Applies to: Cummins/Onan MAJ, Cummins/Onan MAJB engine
Before you start
- Do not tamper with the seal at the center of the mounting bracket; electrical system is not serviceable
Procedure
- Using a 5/8-inch wrench, loosen the pump cover, then remove the cover by hand.
- Remove the filter, magnet and cover gasket.
- Remove the retainer spring from the plunger tube; remove washer, O-ring seal, cup valve, return spring, and plunger.
- Wash all parts (except gasket and seal) in parts-cleaning solvent and blow out with low pressure compressed air.
- Insert the plunger in the tube spring end first and check for free movement and a click.
- Install the plunger spring, cup valve, O-ring seal and washer; compress the spring and install the retainer.
- Check the cover gasket and replace if deteriorated, then install gasket, magnet, filter and cover assembly.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Full service-parts list: Cummins/Onan MAJ →
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.