Changing Fuel Filters: A Guide For 340 Cummins Engines

Changing the fuel filter on a Cummins 340 engine is a relatively straightforward task, but there are a few things to keep in mind. Firstly, it is recommended to have two filters – a primary fuel filter and a fuel-water separator. These filters should be changed annually or every 15,000 miles, whichever comes first. When changing the filters, it is important to be prepared for fuel leakage as they are gravity-fed. It is also recommended to pre-fill the new filters with clean fuel before installation. Additionally, make sure to prime the fuel system after replacing each individual fuel filter to remove air from the system and prevent fuel system components from running dry.

Drain the fuel filter housing

To drain the fuel filter housing on a Cummins 340, you will need to locate the fuel filter housing drain valve. This is usually found on the side of the housing, protruding from the bottom. Attach a section of tubing or a drain hose to the drain valve nipple. Place the other end of the tube into a suitable container to catch the drained fuel.

For a 6.7L Cummins engine, the fuel filter housing is mounted on the driver's side of the engine block. The drain hose will protrude from the bottom of the housing. You may need to use an appropriate fitting to connect the tubing to the drain hose.

For a 1998 Dodge Ram with a 24-valve Cummins diesel engine, the fuel filter housing is located near the brake master cylinder. You will need to drain the fuel from the canister before removing the canister bottom to access the old filter.

For a 2020 model year engine, the fuel filter housing drain valve is located at the bottom of the fuel filter housing cap. Rotate the drain valve counter-clockwise to begin draining the fuel.

Remember to always place a container to catch the drained fuel and to close the drain valve when you're done.

Remove the old filter

To remove the old filter from your Cummins 340, first, locate the filter. The fuel filter is located on the driver side of the engine block, just inwards of and slightly below the brake fluid reservoir.

Place a small drip pan or container underneath the filter to catch any fuel that spills. You can also use a clear container to check for water and other contaminants in the drained fuel.

Next, you will need to loosen and remove the filter. Depending on your model, you may need to use a strap wrench, a 28mm socket, or a 1/2" ratchet to loosen the filter. Be careful not to spill fuel as you remove the filter.

Once the filter is loose, slowly twist it open and remove it from its housing. You may need to reposition your hands to manoeuvre the filter through the wires and out of the engine compartment.

After removing the filter, inspect the inside of the filter housing for any debris or contaminants. This is especially important for CP4-equipped 2019 and 2020 model-year vehicles, as debris could indicate an injection pump failure.

Now that the old filter has been removed, you can discard it and prepare to install the new one.

Insert the new filter

To insert the new filter, you will need to lubricate the replacement filter housing cap o-ring with clean engine oil. Then, install the lubricated fuel filter housing cap o-ring. Next, insert the new fuel filter into the cap so that it is secured in place. Reinstall the fuel filter/cap assembly into the housing. Secure the cap hand tight and verify that the o-ring has sealed properly, then torque to 22.5 ft-lbs (30.5 N-m) with a 28 mm socket; do not overtighten.

Now, locate the engine-mounted fuel filter housing on the driver's side of the engine block just inwards of and slightly below the brake fluid reservoir. Remove the fuel filter housing cap with a 28 mm socket. Remove the fuel filter from the housing and discard it. Install the new fuel filter, then remove and replace the old fuel filter housing lid o-ring (recommend installing a new filter before replacing the o-ring to avoid dropping debris into the filter housing). The fuel filter standpipe is oval-shaped, so you may have to rotate the filter element to find the correct position.

Close the yellow drain valve completely. Reinstall the fuel filter housing lid and torque to 22.5 ft-lbs (30.5 N-m). Cycle the ignition to the "RUN" position (do not start or attempt to start) until the electric fuel pump powers down, then cycle the ignition to the "OFF" position. Repeat this process 10 to 12 times to prime the fuel system.

Start the engine and check for leaks at the fuel filter housing lids and drain valves. Inspect the diesel fuel drained from the filter housings; clean diesel fuel should be clear with a blue or green hue. Cloudy, milky, orange, or dark-colored fuel will generally indicate a fuel contamination issue.

Prime the new filter

To prime the new filter on your Cummins 340 engine, you will need to cycle the ignition to the "ON" or "RUN" position repeatedly. This will activate the electric lift pump, which will power on and begin cycling fuel through the system. This process is known as priming the fuel system and helps to bleed air from the fuel supply.

• Turn the ignition switch to the "RUN" position and listen for the fuel pump.
• The fuel pump will produce a whirling or whistling noise while it is running.
• When the fuel pump powers down (typically 10 to 15 seconds), return the ignition switch to the "OFF" position.
• Repeat this process 10 to 12 times to ensure all air is removed from the system.
• If your vehicle is equipped with a push-button ignition, press the ignition button without placing your foot on the brake pedal to cycle through the "RUN" sequence without cranking or starting the engine.
• If the engine stalls, sputters, or runs rough, the key was not cycled enough times to fully bleed the fuel system.
• It is recommended to cycle the ignition system a minimum of 10 times before attempting to start the engine after replacing the fuel filters.

Additionally, if you are replacing both the chassis-mounted filter and the engine-mounted filter, it is important to prime the fuel system after replacing each individual fuel filter. This helps to prime the filter housing and reduce the amount of air in the system, making it easier to prime the entire system after the second filter is replaced.

Check for leaks

After replacing the fuel filters, it is important to check for leaks. Turn the ignition to the "run" position (do not start or attempt to start) and listen for the fuel pump. You will hear a whirling or whistling noise while it is running. When the fuel pump powers down (typically 10 to 15 seconds), return the ignition switch to the "off" position and repeat this process 10 to 12 times to ensure all air is removed from the system.

If the engine stalls, sputters, or runs rough, the key was not cycled enough times to fully bleed the fuel system. Because injection pumps and injectors wear rapidly in the absence of fuel, it is recommended to cycle the ignition a minimum of 10 times before attempting to start the engine.

After cycling the ignition sufficiently, start the engine and check for leaks at the fuel filter housing lids and drain valves. Ensure that the drain valves are closed.

Additionally, inspect the diesel fuel drained from the filter housings. Clean diesel fuel should be clear with a blue or green hue. Cloudy, milky, orange, or dark-colored fuel generally indicates a fuel contamination issue.

Some users have also suggested draining the fuel filter before removing it, as well as using a strap wrench to remove and install the filters.

Frequently asked questions