Product Description

Interstate-McBee M-3909696 Fuel Injector Return Manifold (Return Line) – 1989–1993 5.9L Cummins 12-Valve

Restore proper injector leak-off flow on your first-gen Cummins. The Interstate-McBee M-3909696 fuel injector return manifold is a direct-fit replacement for 1989–1993 5.9L 12-valve (6BT) applications, installing in the factory routing to maintain OE function and reliability.

Direct-fit replacement: Installs in the OEM location with OE-style geometry for correct routing.
OE function: Maintains proper injector leak-off/return to prevent seepage and air intrusion.
Aftermarket value: Interstate-McBee quality at significant savings vs. OEM box pricing.
Application-specific: Designed for 1989–1993 Dodge Cummins 5.9L 12V (6BT) platforms.

Specifications

Manufacturer	Interstate-McBee
Part Number	M-3909696
OEM Reference	Cummins 3909696
Function	Fuel injector return manifold (injector leak-off line)
Engine	5.9L Cummins 12-Valve (6BT)
Applicable Years	1989–1993
Warranty	Fuel injection parts typically covered for 12 months from installation (see manufacturer policy).

What's Included

(1) Fuel injector return manifold/line assembly

Banjo bolts and sealing washers are not included and should be replaced during service.

Vehicle Fitment

For best results, verify using your engine serial number (ESN).

Dodge (First-Gen) 5.9L Cummins 12-Valve (6BT)
- 1989–1993 D/W-Series 250 & 350 (commonly referred to as “’89–’93 Dodge Cummins”)

Helpful Install Notes

Work on a cool engine; clean the area to prevent debris from entering fittings.
Replace copper sealing washers on injector banjo bolts to ensure a leak-free seal.
Prime the fuel system per service manual after installation and inspect for seepage.

Why Buy From CPP Diesel

First-gen Cummins specialists with ESN-verified fitment support.
Fast shipping and easy returns to keep your truck on the road.
Deep catalog coverage for B-Series fuel, gasket, and timing components.

FAQ

Will this fit all 1989–1993 5.9L Cummins trucks?

Yes—this line is listed for first-gen 1989–1993 5.9L 12-valve Cummins applications. Verify by ESN for edge cases or swapped components.

Does it include banjo bolts or sealing washers?

No—the manifold/line only. We recommend installing new sealing washers and inspecting banjo bolts for damage during service.

How does Interstate-McBee compare to a genuine Cummins part?

Interstate-McBee builds to OEM-equivalent form, fit, and function at a lower price point. If an OEM-boxed part is required, Cummins 3909696 is the genuine number.

What symptoms indicate a failing return manifold?

Fuel seepage around injector leak-off fittings, hard restarts due to air entry, or a line that cracks when disturbed are common signs.

What is the warranty on this fuel injection part?

Fuel-injection category parts from Interstate-McBee are generally covered for 12 months from first installation. Check current manufacturer policy for specifics.