Cummins/Onan — Fuel System Bleeding
Maintenance
From a Cummins/Onan owner's manual covering: 4B3.9, 4BT 3.9, 4BTA 3.9, 6B5.9, 6BT 5.9, 6BTA5.9, B5.9-160, B5.9-175, B5.9-190, B5.9-210, B5.9-230. Check it applies to your exact model before use.
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Before you start
- Do not engage starting motor more than 30 seconds; wait 2 minutes between engagements.
Procedure
- Controlled venting is provided at injection pump through fuel drain manifold; small amounts of air vent automatically if filter changed per instructions.
- Manual bleeding required if filter not filled, injection pump replaced, high pressure lines loosened, initial start, or tank run empty.
- Open vent screw. Operate lift pump plunger until fuel flowing is free of air.
- Tighten bleed screw. Torque 9 N·m [7 ft-lb].
- For Lucas CAV pump, bleed at shown location.
- Air can be vented through fuel drain manifold by operating starting motor.
Tools required
- 8 mm wrench Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 9 N·m [7 ft-lb] bleed screw
Source: Cummins/Onan owner's 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.