Changing Your Lmm Fuel Filter: A Step-By-Step Guide

Changing the fuel filter on a Chevy or GMC Duramax LMM engine is a relatively straightforward process that can be done in about 15 minutes. The first step is to unplug and remove the water-in-fuel (WIF) sensor, allowing it to drain. Next, the fuel filter can be unscrewed and removed, being careful not to damage the sensor. A new filter can then be installed, ensuring that new O-rings are used and that the O-ring on the filter is fully seated before installation. Once the new filter is in place, the WIF sensor can be screwed back on and plugged in, and the bleeder screw on the housing can be loosened to prime the filter. The engine can then be started, and the bleeder screw tightened. It is recommended to change the fuel filter regularly, with some sources suggesting every 10,000 miles as a good interval, especially when using biodiesel.

Unscrew the old filter and screw on the new one

To unscrew the old filter and screw on the new one, you will need a strap wrench and a new fuel filter. You may also need a WIF sensor wrench, which can be purchased online.

First, remove the inner fender well. This will give you the space you need to access the filter. You can also remove the second battery to create more space, if necessary.

Next, unplug and remove the WIF sensor. Let it drain, then carefully remove the old filter. Be sure to use a wrench to avoid damaging the sensor. You may also need to remove the wiring retainers that are on the inner fender.

Now, you can screw on the new filter. Don't forget to use the new O-rings that come with the filter and wipe them with a little diesel for lubrication. Make sure the top O-ring is fully seated before you install the new filter.

Finally, reconnect the WIF sensor plug and tighten it with your wrench.

Remove the fender well

To remove the fender well, you will need to purchase a plastic retainer removal tool from Napa or CarQuest. This will make the job much easier and quicker. You will also need a water sensor removal tool, which you can buy from Lilley via Car Quest for around $10.

Removing the fender well is simple. First, remove the wiring retainers that are on the inner fender. Then, carefully remove the fender well. It might be a good idea to put the truck on a nice comfy stool while you do this. You can also cut a small hole in the fender well, or even cut out a section and make some brackets to screw it back into, and then use that for filter access.

If you don't want to remove the whole fender well, you can just remove the clips and screws on the back portion and drop it down. You don't need to remove the whole thing.

Disconnect the wiring harness

To disconnect the wiring harness, you will need to access the fuel filter, which is located behind the passenger-side fender liner of your LMM Duramax engine. Start by removing the inner fender liner. This will give you the necessary access to work on the fuel filter.

Once the fender liner is removed, locate the wiring harness connected to the fuel filter. It should be a plug-and-socket connection. Gently pull the wiring harness to disconnect it from the fuel filter. Be careful not to damage the connector or the wires.

After disconnecting the wiring harness, set it aside in a safe place where it won't be damaged or disturbed during the rest of the fuel filter change process. Make sure to keep track of which connector it was attached to, as you will need to reconnect it later.

It is important to note that some LMM Duramax engines may have additional wiring harnesses or connections related to other components, such as the engine block heater. Ensure that you only disconnect the wiring harness associated with the fuel filter to avoid any unnecessary complications.

Now that the wiring harness is disconnected, you can proceed with the rest of the fuel filter change procedure, including unscrewing the old filter, installing the new one, and reconnecting the WIF sensor. Remember to refer to a complete set of instructions for the full process of changing the LMM fuel filter.

Loosen the black screw above the fuel filter

To change the LMM fuel filter, you will need to begin by unplugging and removing the WIF sensor. Once the WIF sensor has been removed, carefully unscrew and remove the existing fuel filter. You may need to use a strap wrench or a filter wrench to loosen the filter. It is also important to be cautious when handling the WIF sensor, as it is made of plastic and can be damaged if you apply too much pressure.

When installing the new fuel filter, ensure that you have a new O-ring ready, as this will need to be replaced as well. Screw on the new fuel filter, being careful not to over-tighten it. Once the new filter is in place, you can reconnect the WIF sensor and plug it back in. Now, locate the black screw above the fuel filter and loosen it. This will allow you to access the primer bulb. Push the primer bulb until you see fuel coming out of the screw. Once you see fuel coming out, tighten the screw back up and you can start the truck.

It is important to note that there are different types of fuel filters available, and choosing a high-quality filter is essential for the performance and protection of your engine. Some filters, like the Racor coalescer fuel filter, offer better water removal and longer life. Additionally, using a fuel additive can help improve fuel performance and protect your injectors.

Finally, if you are experiencing issues with your fuel filter, such as frequent "change fuel filter" warnings, it may be due to collapsed or cracked fuel lines, a faulty fuel pressure relief valve, or issues with your injectors or CP3. It is recommended to consult a mechanic or a diesel forum for further advice and potential solutions.

Pump the bulb until fuel comes out of the screw

To pump the bulb until fuel comes out of the screw, you will need to start by locating the bulb. This is usually found on top of the housing. Once you have located the bulb, simply push down on it repeatedly until you see fuel coming out of the screw. This process is known as priming, and it is important to ensure that the fuel filter is ready for use.

It is worth noting that this process may take some time and effort, so it is recommended to be patient and persistent. Additionally, make sure to have a container or rag nearby to catch any excess fuel that may spill out.

Once you see the fuel flowing out of the screw, you can then tighten the screw back down and proceed to the next steps in the fuel filter changing process. Remember to always exercise caution when working with fuel and refer to a professional or a detailed guide if you are unsure about any steps.

Frequently asked questions