Cummins 3957081 – #1 Fuel Injection Line / Injector Fuel Supply Tube for 5.9L ISB

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This genuine Cummins 3957081 #1 fuel injection line restores safe, leak-free high-pressure fuel delivery from the common rail to injector #1 on your 2003–2007 Ram 5.9L ISB. Built to Cummins OE specs with precise bends and flare geometry, it’s the right choice when your original line is cracked, corroded, or has been removed during injector service.

Key Features

• OE rail-to-injector line for cylinder #1 on 5.9L ISB common-rail engines.
• Direct-fit for 2003–2007 Ram 2500/3500 5.9L Cummins (24V common rail) when built with this line.
• Precision-formed steel tube with factory flare and nut geometry for proper sealing.
• Designed for high common-rail pressures and thermal cycling in diesel applications.
• Genuine Cummins part—no guesswork on fitment or quality.

Quick Specs

• Brand: Cummins Genuine
• OE Part #: 3957081
• Position: Cylinder #1 (front of engine)
• Function: High-pressure fuel line, common rail → injector #1
• Engine: 5.9L ISB (24V common-rail), automotive Ram 2500/3500, 2003–2007
• Quantity Required: 1 per engine (for #1 cylinder only)

Verified Fitment

Automotive (Light-Duty):

• 2003–2007 Dodge Ram 2500 5.9L Cummins (24V common-rail)
• 2003–2007 Dodge Ram 3500 5.9L Cummins (24V common-rail)

Industrial / Off-Highway / Other ISB & QSB:

3957081 is also used on various ISB/QSB applications outside of Dodge/Ram. For non-automotive engines, always confirm by Cummins Engine Serial Number (ESN) and current fuel system configuration before ordering.

Often Paired With (Cummins Parts on CPP Diesel)

• Cummins 4988810 – #2 Fuel Injection Line (5.9L ISB, 2003–2007)
• Cummins 4988809 – #3 Injector Fuel Supply Tube / Line (5.9L ISB, 2003–2007)
• Cummins 5289447 – #4 Fuel Injection Line (5.9L ISB, 2003–2007)
• Cummins 4988807 – #5 Fuel Injection Line (5.9L ISB, 2003–2007)
• Cummins 4988806 – #6 Injector Fuel Supply Tube (5.9L ISB, 2003–2007)
• Cummins 3957079 – CP3-to-Rail Fuel Supply Line (5.9L ISB, 2003–2007)
• Cummins 5264181 – Injector Fuel Supply Connector Retainer / Tube Nut (set of 6 per engine)

What’s In the Box

• (1) Genuine Cummins 3957081 injector fuel supply tube / #1 fuel injection line

Installation Notes

• Work surgically clean—any contamination in a common-rail system can damage injectors.
• Route the line exactly like OE; do not bend, kink, or pre-load the tube.
• Start all tube nuts by hand to avoid cross-threading, then torque to factory spec.
• After installation, prime the fuel system and check for leaks at idle and under load.
• Replacing disturbed connector tubes, seals, and tube nuts is strongly recommended.

FAQ

WILL THIS FIT MY 2003–2007 5.9L CUMMINS RAM?

Yes—Cummins 3957081 is the OE high-pressure fuel line for cylinder #1 on most 2003–2007 Ram 2500/3500 5.9L ISB common-rail trucks. Always verify by VIN or Cummins ESN if the fuel system has been modified.

IS THIS THE RAIL-TO-INJECTOR LINE OR THE CONNECTOR TUBE?

This part is the rail-to-injector high-pressure line for cylinder #1. The internal injector connector tube and its nut/seals are separate parts and should be inspected and replaced as needed.

CAN I REUSE MY OLD HIGH-PRESSURE LINE?

Reuse is not recommended. High-pressure lines can work-harden, crack, or develop sealing-cone damage from vibration and repeated torque cycles. Whenever a line is removed for injector or rail service, Cummins recommends replacement.

WHAT ARE THE PART NUMBERS FOR THE OTHER CYLINDERS?

For 2003–2007 5.9L ISB common-rail, the typical OE Cummins line part numbers are: #1 – 3957081 (this part), #2 – 4988810, #3 – 4988809, #4 – 5289447, #5 – 4988807, #6 – 4988806. Always confirm by ESN before mixing components.

IS THIS A GENUINE CUMMINS PART?

Yes—this is a genuine Cummins fuel injection line sourced through CPP Diesel, with factory-correct geometry and tube material for long-term reliability.

Specifications for cummins 3957081