2004.5-2007 Dodge 5.9L Cummins Fuel Lines

Fuel Lines on the 2004.5-2007 RAM 5.9L Cummins

The 5.9L Cummins common rail has two kinds of plumbing. On the high-pressure side, six injection lines run from the rail to the cylinder head, carrying 4,251 to 23,206 psi. Each line meets a connector tube that passes through the head and joins the side of the injector. On the low-pressure side, the supply and return lines use quick-connects at the filter housing, and the return circuit uses banjo fittings at the rail, the CP3 and the injector return.

What fails and why

Cracked #4 and #6 lines are the documented problem. Signs are an external diesel leak at the line, loss of rail pressure and a miss. Torque is the other cause of line trouble. Injection line nuts take 22 ft-lb and should never go over 25-30 ft-lb, and you want a backup wrench at the rail and at the head. Behind each line, the connector tube nut takes 37 ft-lb; if it is under-torqued, it leaks into the return and mimics a bad injector.

Stock replacement vs. upgrade

For a stock truck, replace a cracked line with the correct genuine part for that cylinder. Each position has its own Cummins part number, so you can buy just the line you need, and the BD Diesel line set replaces the lines as a set. For a modified truck, Exergy's high-flow CP3 supply fittings and Dynomite Diesel's oversized universal injection lines are the upgrade parts here. If you are fitting a 6.7L-style CP3 to the 5.9L, the Fleece adaptation kit handles the high-pressure line side.

What we carry

• Cummins genuine injection lines for every position: #1 (3957081), #2 (4988810), #3 (4988809), #4 (5289447), #5 (4988807) and #6 (4988806).
• BD Diesel fuel injector line set (2003-2007) and fuel injector installation kits for 2003-2005 and 2006-2007.
• Exergy Performance fittings: M14x1.5 three-way T, M14x1.5 plug and nut (rail cap), and M12x1.5 to -6AN and -8AN high-flow CP3 supply fittings.
• Dynomite Diesel universal high-pressure oversized injection lines in multiple lengths.
• Fleece Performance Engineering HP fuel line adaptation kit, 5.9L to 6.7L Cummins CP3.

Fitment notes

Order by cylinder number, since each position has its own part number. BD's installation kits split at 2006, so a 2004.5-2005 truck takes the 2003-2005 kit and a 2006-2007 truck takes the 2006-2007 kit. The genuine lines here are listed for 2003-2007 5.9L trucks, which covers the 2004.5 change. 2007 is a split year: trucks built after January 1, 2007 got the 6.7L Cummins, so confirm the engine and verify by VIN before ordering lines.

Frequently asked questions

What torque do the injection lines take?

22 ft-lb, and never more than 25-30 ft-lb. Use a backup wrench at the rail and at the head. The connector tube nut behind each line takes 37 ft-lb.

Which injection lines crack on the 5.9L common rail?

The #4 and #6 lines have a documented cracking history. Cummins issued an updated line with a hold-down bracket. If you tow or travel far from home, carry spare lines.

I smell diesel and the engine has a miss. Could it be a line?

It could. A cracked injection line shows up as an external diesel leak at the line, loss of rail pressure and a miss. Look at #4 and #6 first, and check that the connector tube nuts are at 37 ft-lb, since a loose one leaks into the return instead of outside the engine.

Not sure what fits? Call the shop at the number in the header, or use the fitment checker on any product page. We install everything we sell.