Replacing The Fuel Filter In A Cummings 350 Engine: Step-By-Step Guide

Changing the fuel filter on a Cummins 350 engine is a relatively simple task that can be done at home, saving you a trip to the dealer. The fuel filter is located on the driver's side of the engine, below the intake manifold. The first step is to drain the fuel by attaching a hose to the water drain valve at the bottom of the filter housing and routing it to a catch pan. Once the filter is drained, you can remove the housing. On a Cummins 350 engine, you will need to unplug the water-in-fuel sensor before lowering the canister and filter out through the bottom of the vehicle. When reinstalling the new filter, make sure to replace and lubricate the canister O-ring. To prime the system, cycle the key without starting the engine 10 to 20 times. It is important to change your fuel filter regularly, as a clogged filter can lead to fuel starvation and potentially damage injectors, injection pumps, and lift pumps.

Draining the fuel

Before you start, make sure you have a new fuel filter, a catch pan or bucket, and some basic hand tools. You'll also need some new fuel filter lubricants and a replacement canister O-ring.

The first step is to drain the fuel. Attach a hose to the nipple on the bottom of the filter housing and route it to a catch pan. Then open the valve and drain the fuel.

For a 5.9L Cummins, the cap is removed and the filter lifts up and out. For a 6.7L Cummins, you first need to unplug the water-in-fuel sensor before lowering the canister and filter out through the bottom of the vehicle.

The 5.9L filter is accessible from the top of the engine, while the 6.7L filter is accessed from under the truck.

Once the filter is drained, you can remove the housing. Remember to replace and lubricate the canister O-ring when reinstalling the filters.

Removing the housing

To remove the housing of the fuel filter on a Cummins 350 engine, you will need to first drain the fuel from the filter canister. Place a drip pan underneath the filter and unscrew the Water in Fuel (WIF) sensor to drain the fuel. Once drained, close the sensor and remove the filter, placing it in the pocket between the frame and motor mount.

The next step is to remove the wiring harness from the WIF sensor. You can either cut the wires and place them in a bag, or coil them up and secure them in a bag to prevent dirt and water ingress.

Now, you will need to remove the filter housing. This can be done using a 1/2" ratchet and extension, or a strap/band-type filter wrench. Place a bag over the housing before removal to catch any residual fuel. Be careful not to strip the bottom 1/2" port as you loosen the housing.

It is also possible to access the filter housing from above the engine, without removing the fender liner. This method may be easier for some, but care must be taken not to crack the filter housing.

Installing the new filter

To install the new filter, first lubricate the canister O-ring. Then, place the new filter into the housing. For the 5.9L, simply lower the filter into the housing and screw the cap back on. For the 6.7L, feed the new filter through the wires and rest it between the throttle linkage, starter, and throttle cable. Then, fill the new filter with fuel. Once full, lift the filter and screw it back into the housing.

Priming the system

To prime the fuel system of a Cummins 350, you must first identify whether your engine is a 12-valve or a 24-valve. The 12-valve engine has a mechanical lift pump and should be primed by pumping the bulb on the lift pump, which is located below and to the right of the filter canister. The 24-valve engine, on the other hand, has an electric lift pump and can be primed by bumping the starter and letting the lift pump run.

If you have a 12-valve engine, follow these steps:

• Locate the lift pump below and to the right of the filter canister.
• Pump the primer bulb on the lift pump approximately 50 times. You may need to use a broom handle or paint roller extension stick to apply sufficient force.
• Tighten the bolt on the inlet side of the filter housing.
• Continue pumping the primer bulb a few more times until you hear the overflow valve squeak.
• Attempt to start the engine. It may stumble for a few seconds before running smoothly.

If you have a 24-valve engine, follow these steps:

• Turn the key to the "on" position without starting the engine. This will activate the electric lift pump.
• Let the lift pump run for approximately 25 seconds.
• If there is still air in the system, loosen the return line banjo bolt on the injection pump and repeat the process until fuel comes out.
• Tighten the banjo bolt.
• Attempt to start the engine. It may run a little rough at first, but bringing up the RPMs for a short time should resolve this.

Alternatively, you can prime the fuel system by pressurizing the fuel tank with compressed air. This method can help expose leaks in the supply line.

Using the correct tools

To change the fuel filter on a Cummins 350 engine, you will need a few tools. The exact tools will depend on the model of your Cummins engine. For a 5.9L Cummins, you will need a 1 1/8-inch socket to remove the filter cap. You may also need a breaker bar to get the filter cap off. A special wrench is required to remove and install the water-in-fuel sensor. A flare nut wrench will be useful for working on fuel lines. A cheater bar or a 2-foot cheater can also be handy. A ratchet, extensions, and a U-joint may be required to reach the filter cap. A 1/2-inch nut driver or flat-head screwdriver is needed to open the relief valve on a Duramax engine. A clear hose can be attached to the water drain valve to help with draining the fuel. A funnel with a twist shut-off and a long clear tube can be used to fill the new filter with fuel.

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