Removing Fuel Regulator Pressure From Your Duramax Lml

The CP4 fuel pressure regulator in the LML Duramax engine is prone to failure, which can lead to catastrophic damage to the fuel system. To prevent this, one can install an aftermarket fuel pressure regulator, such as the CP4 Exergy System Saver or the LinCo fuel pressure sensor fooler. The installation process involves removing several parts to access the fuel pressure regulator and then replacing it with the new one. This process requires specific tools and mechanical knowledge, so it is recommended to be performed by experienced individuals.

Removing the fuel filter pressure sensor

To remove the fuel filter pressure sensor, you will need an Allen wrench or socket, a 5/8-inch or 16mm socket, and a 5/8-inch wrench. You will also need to remove the air intake tube to gain access to the sensor. The grid heater power supply cable can also be removed, although this is not necessary.

With access to the factory sensor, and because you are working with a fuel system-related component, the sensor (as well as everything in its immediate vicinity) should be hit with brake cleaner, followed by compressed air. Then you can unthread the sensor, which can typically be done by hand. After that, extracting the factory adapter fitting calls for a 5/8-inch wrench to break it loose.

LinCo recommends using a diesel fuel-rated Teflon sealant on the delete plug's threads. The delete plug itself is installed in the factory sensor base via the aforementioned Allen wrench or socket. Next, the plastic fooler connects to the factory plug. From there, the fooler and plug can be secured to the engine wiring harness by way of zip ties, the air intake tube can be reinstalled (along with the grid heater power supply cable, if it was also removed) and the install is complete.

Installing a fuel pressure sensor fooler

If you're the owner of a 2011-2016 LML Duramax, you may be familiar with the fuel filter restriction sensor, which monitors vacuum pressure between the filter and CP4 pump. Over time, this sensor can fail in two ways: electrical failure and sensor leaks. This can cause a "Change Filter" message, a hard-starting truck, and even a fuel leak.

A fuel pressure sensor fooler can fix both of these issues. The fooler plugs into the factory harness and sends the correct signal to the ECM, ensuring normal fuel pressure (vacuum). This resolves the electrical issue associated with the factory fuel filter restriction sensor.

To install a fuel pressure sensor fooler, you will need an Allen wrench or socket, a 5/8-inch or 16mm socket, and a 5/8-inch wrench to remove the factory sensor. You will also need to remove the air intake tube to access the sensor. It is recommended to clean the sensor and its surrounding area with brake cleaner and compressed air before unthreading the sensor.

Once the factory sensor is removed, you can install the delete plug. It is recommended to use a diesel fuel-rated Teflon sealant on the delete plug's threads. The delete plug is installed in the factory sensor base using an Allen wrench or socket. The plastic fooler then connects to the factory plug. Finally, the fooler and plug can be secured to the engine wiring harness using zip ties, and the air intake tube can be reinstalled.

For trucks without a lift pump, you will also need to prime the fuel system by cracking the bleeder screw loose, pumping out all the air from the system, and then re-tightening the screw.

Removing the air intake tube

To remove the air intake tube, you'll need to gain access to the factory sensor. This will require an Allen wrench or socket, a 5/8-inch or 16mm socket, and a 5/8-inch wrench.

First, remove the air intake tube to gain access to the sensor. You can also remove the grid heater power supply cable to give yourself more room to work, although this step is not necessary.

Next, clean the sensor and its immediate surroundings with brake cleaner and compressed air.

Now, you can remove the sensor by hand. After that, use a 5/8-inch wrench to loosen the factory adapter fitting.

Finally, install the delete plug using a diesel fuel-rated Teflon sealant on its threads.

Removing the A/C compressor

To remove the A/C compressor, first unseat the belt from the A/C compressor. You should know how to do this. Next, pull the electrical connectors from the A/C compressor radiator line. There are two of them. Then, pull the coolant line off the thermostat housing. You may want to drain some coolant out of the petcock of the radiator before you do this.

Now, you can pull the A/C compressor at any time. There are four bolts to remove and then you can lay it over to your left on the passenger's side of the bay.

With the A/C compressor gone, you now have a ton more access to the FPR. Zip tie the thermostat coolant line out of the way.

Removing the coolant line

To remove the coolant line, first, you'll want to pull the coolant line off the thermostat housing. It's recommended to drain some coolant out of the petcock of the radiator before you do this to avoid spillages. You can use rubber stoppers (corks) to plug any dribbles.

Next, pull the coolant hose off the intercooler. You'll need to stop this up, so be prepared with a siphon hose or a small container to catch the excess.

Now, zip tie the thermostat coolant line out of the way.

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