Cummins/Onan — Injector - Replacement
Repair & overhaul · fuel injector
From a Cummins/Onan service manual covering: 4B3.9, 4BT 3.9, 4BTA 3.9, 6B5.9, 6BT 5.9, 6BTA5.9. Check it applies to your exact model before use.
Applies to: Cummins/Onan 4B3.9, Cummins/Onan 6BTA5.9
Before you start
- Early model injectors (pre 1991) have a 9 mm injector tip which cannot be used in engines built in 1991 or later; these engines use a 7 mm injector tip.
Procedure
- Clean around the injectors.
- Disconnect the high pressure fuel supply lines and fuel drain manifold.
- Soak the hold-down nut with rust penetrating solvent for a minimum of 3 minutes.
- Hold the injector body with an adjustable wrench and loosen the hold-down nut with a 24 mm box wrench.
- Remove the injector; use an injector puller if difficult.
- Clean the injector nozzle bore.
- Assemble the injector and new copper sealing washer; use only one copper washer.
- Apply anti-seize compound to the hold-down nut threads.
- Install the injector and tighten to 60 N•m [44 ft-lb].
- Assemble the fuel drain manifold and high pressure lines; bleed air.
Tools required
- 24 mm box wrench Amazon
- adjustable wrench Amazon
- brass drift pin Amazon
- hammer Amazon
- injector puller 3823276 Amazon
- injector bore brush 3822509 Amazon
- 24 mm deep well socket Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 60 N•m [44 ft-lb]
Full service-parts list: Cummins/Onan 4B3.9 →
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.