Product Description
Genuine Cummins
Cummins 3900808 — 9mm Fuel Injector Sealing Washer (Copper)
MPN: 3900808 | Also Known As: injector washer, injector seal, nozzle seal | Cross-Refs: Bosch 2430105026
Why This Part
- ✓ OE copper washer for proper injector-to-head sealing.
- ✓ Correct 9mm size for early 1st-gen 5.9L Cummins.
- ✓ Prevents combustion leaks and maintains spray pattern.
- ✓ Sold individually — order 6 per engine.
OE Fit 9mm Tip 6 Req.
Quick Specs
| Type | Fuel injector sealing washer (copper) |
|---|---|
| OE Part # | 3900808 |
| Injector Tip Size | 9mm (early 1st-gen) |
| Qty Required | 6 per engine (sold individually) |
Verified Fitment (Automotive)
| Year Range | Engine | Chassis |
|---|---|---|
| 1989–1991 | 5.9L 12-Valve (VE pump) with 9mm injectors | Dodge 250/350 (1st Gen) |
Compatibility Notes: This washer is for 9mm injector tips. Later 1st-gen trucks with 7mm injectors use a different washer. Always confirm tip size or ESN before ordering.
Often Paired With
- Injector install kit / return line seals (year-appropriate)
- Injector seat cleaning tools to prep the bore
What’s In The Box
- (1) Genuine Cummins 9mm Injector Copper Washer (3900808)
- Order 6 for a full engine set (sold individually).
Install Tips
- Clean the injector seat; do not reuse old copper washers.
- Verify injector tip size is 9mm before installation.
- Torque injector hold-downs to spec and recheck after heat cycle.
FAQ
WILL THIS FIT MY 1989–1991 5.9L CUMMINS?Yes—this 9mm copper washer fits early 1st-gen 5.9L applications with 9mm injectors. Confirm tip size or ESN if unsure.
HOW MANY WASHERS DO I NEED?Order 6 washers per engine (one per injector).
IS THIS FOR 9MM OR 7MM INJECTORS?This is the 9mm washer. Later 1st-gen trucks use 7mm injectors and require a different washer.
IS THIS A GENUINE CUMMINS PART?Yes—OE Cummins 3900808 copper injector sealing washer.
CAN I REUSE MY OLD WASHERS?Reusing can cause combustion leaks and poor spray pattern. Always install new washers on reassembly.
Product Videos
Custom Field
Vehicle Year 1989,1990,1991
Vehicle Make DODGE
ENGINE 5.9L
Part Type 9mm Injector Sealing Washer
