The $40 LML Duramax Fueling Fix

• March 13, 2022
• Story By
  Mike McGlothlin

Whether it’s repairs, performance or simple upkeep, the words cheap and diesel don’t usually go hand-in-hand. But when LinCo Diesel Performance—a Missouri-based truck shop—began to notice a pattern problem on the diesel-powered ’11-’16 GM trucks they were working on, they decided to do something about it. The problem, which is exclusive to the 6.6L LML Duramax V-8, is a faulty fuel filter restriction sensor. Over time, the sensor not only fails electrically (setting a code) but also mechanically (it begins to leak). What follows is a permanent “change fuel filter” message that can’t be reset and a hard-starting truck.

LinCo’s fix, a fuel pressure sensor fooler, solves both of the aforementioned issues, installs in minutes and retails for just $39.99. An optional fuel pressure sensor delete plug (two to choose from) can be added in with the fooler for a few more bucks and a snubber can also be purchased by truck owners who’ve installed an aftermarket electric fuel pressure gauge. Bottom line: for less than 50 bucks a highly-common problem is solved for good and you and your Duramax can get back to work.

The Problem

On the electrical side of the equation, the factory fuel filter restriction sensor—which is just a vacuum sensor—is notorious for failing and sending a faulty signal to the ECM. The ECM responds by displaying the “Change Fuel Filter” message on the dash. When this happens the change fuel filter message will not go away (and can’t be reset). On the mechanical side of the equation, the sensor is known to leak. On ’11-’16 GM HD’s without a lift pump (an aftermarket add-on), this causes a long crank, no start situation because the fuel system loses its prime. On trucks that are fitted with a lift pump, you’ll have an external fuel leak.

The Fix

The factory fuel filter restriction sensor’s only job is to report the presence of excessive vacuum pressure between the fuel filter and the CP4.2 high-pressure fuel pump to the ECM. It is located on the passenger side of the engine just below the throttle valve—and this is its fix. A simple piece, LinCo Diesel Performance’s LML fuel pressure sensor fooler retails for $39.99. The fooler (shown) comes standard with a delete plug to take the failure-prone factory sensor out of the equation completely.

The Fooler

For seamless integration and an easy install, LinCo’s fuel pressure sensor fooler connects directly in-line with the factory harness, doing so by accepting the OEM male connector. The fooler sends the correct signal to the ECM for normal fuel pressure (vacuum). This solves the electrical issue associated with the factory fuel filter restriction sensor. Think of the small plastic connector as a solution rather than a fooler. No more permanent “0% Fuel Filter Life or “Change Fuel Filter” messages.

O-ringed Delete Plug

The fuel filter pressure sensor delete plug remedies the mechanical, leak side of the two-fold problem by allowing you to remove the factory fuel filter restriction sensor. The plug utilizes an O-ring and also features 1/8-inch NPT female threads, which makes it the perfect location for adding an aftermarket fuel pressure sensor, should you choose to install one.

Pipe Plug (Standard) and Snubber (Optional)

It’s worth noting that LinCo does not ship its product with the pipe plug installed in the delete plug fitting. This is done in case the customer plans to install a snubber for an aftermarket fuel pressure sensor gauge. For the latter customers, LinCo offers a snubber with its fuel pressure sensor fooler as an add-on option—and the company highly recommends opting for one if you plan to run a fuel pressure gauge. A snubber can be tacked on to your order for an additional $27.99.

Dead Giveaways

Whether or not an LML-equipped GM truck has a lift pump installed or not, the factory fuel filter restriction sensor is useless—but it’s especially irrelevant on truck’s with a lift pump such as the FASS system shown here. When the factory sensor fails in this type of application the telltale sign is an external fuel leak. On ’11-’16 Duramax trucks not equipped with a lift pump, a failing factory sensor will yield you a long crank, no-start scenario due to the fuel system losing prime.

Removing The Factory Sensor

Installing LinCo’s fuel pressure sensor fooler requires an Allen wrench or socket, a 5/8-inch or 16mm socket and a 5/8-inch wrench (to remove the factory sensor). It also requires removal of the air intake tube to gain access to the sensor. For even more breathing room the grid heater power supply cable can also be removed, although this step isn’t 100-percent necessary. With access to the factory sensor, and because you’re 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 (shown above), 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.

Installing The Delete Plug

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. For truck’s without a lift pump, the fuel system will have to be primed the factory way, by cracking the bleeder screw loose, pumping all air out of the system and then re-tightening the bleeder screw.