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The fuel systems of diesel trucks have special needs that the gasoline equivalent does not. Additional filtration and even a way to remove water from the fuel is a must-have. Paying attention to the fuel system on your truck can help prevent problems such as loss of power, as well as hesitations and hiccups, due to fuel starvation, or interruption. For the needs of a particular Ram truck, we decided that fuel system upgrades including a Pureflow AirDog II-4G Fuel Preporator, and the DieselRx fuel sump would be a wise choice. These additions will upgrade the existing fuel system in terms of filtration and delivery efficiency.
About The Truck
The test vehicle used was our 2008 Dodge 2500, with a 6.7-liter Cummins. The truck is largely unmodified, sans an Edge tuner, and leveling air bags. The truck is used primarily for hauling toys to the desert, lake, or other recreation destinations.
The truck owner has lamented to us the tedious task of accessing and changing the OEM water-fuel separator. Located deep inside the engine bay, this vital component of the fuel system is only reachable from underneath, or with the driver-side fender liner removed. He recalls consistently throwing away his clothes after being soaked in diesel, during the seemingly simple task of changing the filter. An owner who looks after his vehicles, he keeps his tank full of diesel to avoid excess air in the tank harboring water vapor, which would condense and collect in the fuel. Even with such a precaution, diesel fuel is vulnerable to water contamination, and microbial growth. Such intrusions can have serious consequences to the engine’s performance and longevity.
The AirDog II-4G Fuel Preporator
Fuel System Upgrades: What’s What…
When it was time to decide which aftermarket lift pump we needed to include with our fuel system upgrades, we learned the AirDog Fuel Preporator system is available in three configurations; AirDog, AirDog II, and the AirDog II-4G. We elected to install the last of the list, the AirDog II-4G is the top of the range and features a unique system to ensure the fuel reaching your engine is as clean as possible.
Featuring a low-amperage motor driving a gear rotor pump, the AirDog is not just a replacement fuel filter. The AirDog is a full fuel-purification system in that it virtually eliminates all water, particulate matter, and entrapped air from diesel fuel. While you may be familiar with the importance of removing water and dirt from fuel, entrapped air may be an enemy you weren’t even aware of factoring into your diesel performance package.
Entrapped air occurs when diesel fuel is sloshed and agitated in the tank, forming bubbles. These tiny bubbles are suspended in the diesel fuel and do not rise to the surface of the fuel as quickly as gasoline because of the increased viscosity of diesel. Unable to escape the suction of the fuel pickup, these bubbles are drawn into the fuel system and travel downstream.
Once the air is in the fuel lines, the tiny bubbles begin to congregate and form larger bubbles. Soon, a large bubble is formed, and an interruption in fuel delivery is traveling towards your injectors. By cavitating the fuel delivery with air, you may experience engine hesitations, hiccups, and interruptions in power. To illustrate the action of this filter, AirDog engineered a cutaway display proving the effectiveness of the system. Seeing is believing.
The AirDog II-4G is designed to operate at flows and pressures beyond the maximum requirements of the engine. It receives fuel from the fuel tank containing entrapped air/vapor, particulate contaminants, and unknown quantities of water. The AirDog fuel system upgrades remove these contaminants by way of conventional filtration and water separation. It also applies a low-pressure vacuum to draw air or vapor from the fuel and return it to the tank. This way the only fuel making it to the engine is clean, and clear rather than foamy, and potentially contaminated.
Fuel System Upgrades: The DieselRx Fuel Sump
Machined from aircraft-grade aluminum, and clear-anodized for durability, the DieselRx fuel sump provides efficient and reliable fuel delivery.
By working with gravity to pull fuel from the bottom of the tank, DieselRx overcomes the natural pitfalls of the draw straw. DieselRx recommends this option in diesel applications as the fuel sump can maximize the utility of your stock fuel capacity along with other benefits, including the elimination of “quarter tank starvation”.
Installation Of Our Fuel System Upgrades
It should be noted that if you decide to install one of these fuel system upgrades but not both, the plumbing and wiring will be different. Because we decided to install both simultaneously, the two units are plumbed together from the start. The first step of this installation is to make sure you have a minimal amount of fuel remaining in the tank. With the truck on the lift, we turned to the bench for assembly of the AirDog bracketry.
The AirDog brackets and spacer are constructed of a high-strength polymer for lightweight, and easy assembly. No drilling of the frame is required, and various hole spacing makes it possible to vertically locate the AirDog where you want it.
A steel U-channel makes up the cradle for the AirDog filter unit. The kit supplies all the necessary hardware to mount the unit neatly. With the brackets all assembled and the AirDog affixed, we take the supplied pipe fittings and prepare them for installation into the billet aluminum AirDog body. A little anti-seize on the threads will ensure no galling takes place between the fitting and the body.
Mounting the assembly on the frame rail is as simple as choosing a spot, central for plumbing reach, and accessible for service. We decided to locate the filter in line with the rear edge of the driver’s door on the outside of the frame. This will make kneeling to change the filters a simple and mess-free job. No more diesel-soaked shirts.
Tightening the bolts, the physical installation of the AirDog is complete. Changing gears we switched over to the DieselRx sump. We had to jump between the two fuel system upgrade kits, installing them simultaneously because when installed in conjunction, they rely on each other for plumbing and wire routing. The tank was nearly empty when we put the Dodge on the lift but as is the case with nearly any vehicle, some unusable fuel remains trapped in the valleys of the tank.
The next step marked the point of no return. We identified the lowest part of the tank as the area underneath the OEM lift pump and fuel-level sender. This was to be the location of our new fuel sump. The next step was to drill a pilot hole and drain the remaining two gallons of diesel from the tank. We were aware that the sending unit would be right on the other side and were cautious not to damage it as we drilled through the exterior.
With the last drops of fuel finally out of the tank, we mustered up our courage and broke out the hole saw for the second of our fuel system upgrades. Delicately cutting, we proceeded in pulsed rotations until finally the saw grabbed and we knew we were through. Prying the small disc out of the hole we de-burred the opening, and wiped it clean of any plastic shavings from inside.
With our new access, we looked to the next step in the installation. The backing plate for inside the tank is made up of two halves. With the small hole drilled, the two halves can be easily inserted into the tank. These two plates include threaded holes for the externally mounted sump to engage. The kit provides a template for the drill pattern onto the tank. We drilled the four holes, one on either side of the parting line on each plate.
With the first holes drilled, we fed the plates into the opening and threaded the supplied studs into them. With the plates centered over the hole and aligned for the bolt pattern, the sump could be mocked in place, and the remaining holes drilled.
Finally, with the alignment studs removed, we could install the sump. We applied the massive O-rings in their machined grooves and assembled the stainless hardware with the respective rubberized lock washers. The considerable thickness of the O-rings will accommodate the textured plastic of the gas tank and prevent leaks.
We took care to think ahead and clock the outlet of the sump to work with the 90-degree fitting included in the pre-made fuel lines. The quick disconnect fitting points straight out the driver’s side for perfect plumbing.
Plumbing became the major endeavor for the remainder of the installation of our fuel system upgrades. To disable the lift pump, but retain the sending unit, the AirDog-supplied wiring harness removes power to the pump. To access the lift pump and modify it for a return line adaptation we dropped the tank. With the tank out we removed the lift pump and installed the AirDog return line fitting and internal hose.
The pre-made lines of the Airdog kit come with pre-crimped connectors for fuel delivery to the filter, engine, and return to the tank via the original location in the engine bay. When using a DieselRx sump, the return line must be modified and relocated from the engine bay to the top of the fuel tank. We spliced into the line, and with the supplied push-lock fitting made the connection to the lift pump turned fuel-return.
Under the hood, a few fittings must be changed to accommodate the bigger volume fuel lines. Compared to the stock and AirDog fittings, we understand the claim that this system flows beyond the maximum needs of the engine, they mean it,
With the tank on the way back up under the bed, we made the final connections with the return line and wiring harness.
Securing the tank in the original straps, all that was left was the satisfying click of quick-disconnect fittings, and some light wiring. We connected all the lines to the AirDog, sump, and engine. The plug-and-play harness makes wiring as simple as a few connectors, a power, and a ground. With the loom routed into the engine bay, we connected the relay box and leads. With everything routed to our liking, away from rotating, hot, or sharp objects — we applied a few zip ties to tidy up the appearance.
Diesel engines require fuel priming when run dry or when they undergo an upgrade as extensive as this. With the fuel-water separator removed from the AirDog, we filled it with diesel before reinstalling it. Cycling the key on and off kicked on the AirDog pump pushing fuel up to the engine. After a few cycles, the engine started. We confirmed there were no leaks, and we were done. The clean appearance makes these parts look like they belong, and the quality materials mean they will last.
