Improving Diesel Performance








Installing the Airdog II Lift Pump for Improved Diesel Performance

By Tim Walton

The AirDog II is a fuel/air separation system combined with a high-performance lift pump that not only provides more fuel for performance-enhanced trucks, but also removes air, water, particulates and vapor to maintain optimal fuel flow and delivery. The lift pump serves to provide a high volume of diesel fuel to the injection pump, which is what increases the pressure before the fuel is injected into the engine.


By removing entrained air from the fuel it improves injection timing, increasing power and giving you a better fuel burn. Because entrained air and vapor are compressible, their presence in the injector delays the pressure buildup and therefore delays or retards the injection timing.

In addition, inconsistent air bubble sizes that naturally occur in stock systems produce an inconsistent volume of air entering the injector from injection to injection, which not only means retarded injection timing, but inconsistent retarded injection timing, which is even worse.

What does this mean to you? Getting rid of the air produces good results. It can help improve fuel economy while reducing exhaust emissions, giving you better throttle response and top end power. The better filtration provides optimal fuel system lubrication and can help give you longer injector life.

Here’s how the guys at Mobile Diesel installed the system.

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Down at Mobile Diesel Services they’ve installed quite a few AirDog systems and they prefer to drop the stock fuel tank rather than doing a bed-off installation. Even if you’re installing the AirDog in your driveway, it’s probably easier for a couple guys to drop the tank instead of removing the bed itself.

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Pre-assembling the bracket and AirDog setup is a good idea to confirm the best mounting location.

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If you’re doing this install on a rack, a transmission jack works great for supporting the weight of the fuel tank on a broader surface—as well as allowing you to lower and move the tank.

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Remove the clamps that hold the filler hose and other breather hoses from the gas tank.

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Unplugging and disconnecting the wiring and hoses that go to the fuel module is one of the trickier steps to this install. The top of the tank is not only hard to reach but also difficult to see.

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When you take off the straps that hold the tank in place, be sure to lift up on the straps to remove them from the notched side to avoid bending the straps, which would make them harder to reinstall.

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If you want to leave the tank on the transmission jack, centering it on the jack and strapping it down is a good idea. The tank must be stable for removing the fuel sending module.

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The top of the tank can be pretty dirty. It’s important to clean the area around the module before you start disassembly to prevent getting dirt or debris inside the fuel tank. The guys at Mobile Diesel use compressed air to do some of the cleaning.

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A retaining ring holds the module in place. Use a screwdriver and a hammer to spin the ring free so you can remove the unit.

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Since the guys ended up mounting the AirDog II outboard of the frame rail on this short bed pickup, they used the supplied spacer so the bracket clears the parking brake cable.

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When removing the module, be sure not to bend the fuel level assembly. Empty the diesel from the lower fuel cup.

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Since the AirDog II uses the stock feed and return lines as the return and pump bi-pass lines, you need to clear out a spot on the module to drill an additional hole for the new suction feed line.

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A small pair of diagonal cutters can be used to remove some of the ribs from the plastic module. The mechanic, Matt, has done a few of these and knew exactly how much to remove for the new fitting.

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A carbide bit is used to clean up the surface in preparation for making a good seal.

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After starting with a smaller pilot bit, Matt finished up with a 5/8-in. bit to make the 5/8-in. hole, which the new fitting requires.

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Since the AirDog uses an external pump, gutting the module of the stock pump and other associated components frees up room.

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Make sure to drill extra holes (as noted in the instructions) to allow enough diesel to make it into the fuel cup so you don’t starve the newer high-flow pump.

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Once Matt had determined the location for the new suction tube, he used the bracket as a guide for the location of the holes on the outside of the cup.

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Using the included nuts and bolts, you can fasten the bracket that holds the new suction tube in place.

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Reuse the clamps which held the stock lines in place to hold the suction tube. Clamp the new flexible hose to the new fitting in the top of the unit.

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Matt cut a small length off both ends of the flexible hose, as well as the suction tube itself to shorten it a bit. Make sure the unit is fully extended before you cut any length from your hoses.

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The assembled module uses the new fittings for the feed line and takes advantage of the stock lines for a return.

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Make sure the seal for the module on top of the fuel tank is clean and clear of any debris.

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Have a helper hold the module from spinning while you use a hammer and a punch or screwdriver to turn the ring back to the locked position.

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Once you have the module reinstalled you can use the transmission jack to put the tank back into place. Reinstall the straps that hold the tank in place. Make sure you have the new fitting pointed in the right direction to route the fuel lines.

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In this install, the guys used the provided spacer with the mount to clear the emergency brake lines that run along the frame rail where they installed the pump.

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Tap into the stock fuel pump wiring to get the signal wire for the provided harness. The system gets dedicated power from the battery to supply the pump using a larger gauge wire and employing a relay to trigger the power.

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Make sure the fittings are in the right orientation to each other to make it possible to install them both, and don’t over-tighten either of them.

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Replace the fitting into the injection pump with the quick-connecter to accept the provided high-pressure hose.

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Ensure you have efficient routing and run the lines where they are well protected and tucked against the frame rail. Use the provided barb unions to make lines that are the correct length.

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The finished AirDog II unit is well protected on the frame rail where it allows easy filter access for maintenance.

Contact: PureFlow AirDog; (877) 421-3187;


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