fass fuel system 5.9 cummins installation instructions
Fass Airflow systems enhance diesel performance, offering increased fuel flow and filtration for the 5.9 Cummins engine, ensuring reliability and power gains.
Overview of the Fass System
The Fass Airflow System is a complete fuel delivery solution designed to address common issues with factory fuel systems in the 5.9L Cummins diesel engine. It replaces the stock lift pump with a high-flow, gear-driven pump, ensuring a consistent and adequate fuel supply, even under demanding conditions.
Key components include a fuel tank sump for maximizing fuel draw, a high-capacity fuel filter, and a water separator to protect the injection pump. The system aims to eliminate fuel starvation, improve fuel filtration, and enhance overall engine performance. Fass systems are known for their durability and ability to support increased horsepower levels achieved through engine modifications. Proper installation is crucial for optimal functionality and longevity.
Benefits of Installing a Fass System
Installing a Fass Airflow System on your 5.9 Cummins delivers numerous performance and reliability advantages. Primarily, it eliminates fuel starvation issues common with the stock lift pump, especially when towing or adding performance upgrades. The increased fuel flow supports larger injectors and higher horsepower builds, ensuring the engine receives sufficient fuel under load.
Improved fuel filtration protects sensitive injection components from damaging contaminants, extending their lifespan. The integrated water separator prevents corrosion and maintains optimal fuel quality. Furthermore, a Fass system often results in quieter operation compared to the factory pump. Ultimately, it provides peace of mind and enhanced engine durability, maximizing the potential of your Cummins engine.

Pre-Installation Preparation
Thorough preparation is key for a smooth Fass system install; gather necessary tools, verify all parts are present, and safely prepare your 5.9 Cummins.
Tools Required for Installation
Successful Fass system installation demands a specific toolkit. You’ll need a socket set (metric and standard), including extensions and a ratchet. Wrenches, both open-end and box-end, are crucial for various fittings. Fuel line disconnect tools are essential for safely removing factory lines. A drill with various bit sizes will aid in mounting the pump and brackets.
Additionally, a screwdriver set (Phillips and flathead) is necessary. A hose cutter or sharp utility knife ensures clean fuel line cuts. Safety glasses and gloves are paramount for protection. A torque wrench is vital for securing fittings to the correct specifications, preventing leaks. Finally, a multimeter will be needed for electrical connections, and potentially a fuel pressure gauge for post-installation checks.
Parts List Verification
Before commencing installation, meticulously verify all components against the parts list included with your Fass system. This prevents mid-installation delays due to missing items. Confirm the presence of the Fass pump, fuel tank sumps (draw straws), fuel filter, water separator, mounting brackets, and all necessary hoses and fittings.
Inspect all lines and connections for damage during shipping. Ensure you have the correct wiring harness and relay for the pump motor. Check for any included instructions specific to your Fass model. A complete inventory now saves significant frustration later. Document any discrepancies and contact Fass customer support immediately to resolve them before proceeding.
Vehicle Preparation (5.9 Cummins)
Prior to installation, disconnect the negative battery terminal to prevent electrical shorts. Ensure the vehicle is parked on a level surface and securely blocked. Drain as much fuel as possible from the stock fuel tank to minimize spillage during line removal. Locate the factory fuel lines and familiarize yourself with their routing.
Prepare a clean workspace and protect sensitive components from debris. Gather necessary safety equipment, including eye protection and gloves. Note the location of any existing fuel filters or water separators for removal. Document the original fuel line connections with photos for easy reassembly if needed.

Installation Steps: Fuel Tank to Fass Pump
Begin by carefully removing the factory fuel lines and installing the Fass fuel tank sumps, then securely connect new fuel lines to the Fass pump.
Removing the Stock Fuel Lines
Carefully disconnect the stock fuel lines from the fuel tank and the fuel filter housing. Ensure you have appropriate containers ready to catch any spilled diesel fuel, as it’s messy and flammable. Use fuel line disconnect tools to avoid damaging the lines or fittings – forcing them can lead to breakage and fuel leaks.
Label each line as you disconnect it to simplify reassembly if needed, though these will be replaced. Pay close attention to the routing of the lines, as this will inform the path for the new Fass fuel lines. Thoroughly clean the area around the fuel tank and filter housing to remove any dirt or debris before proceeding with the installation of the Fass system components. Safety glasses and gloves are highly recommended during this process.
Installing the Fass Fuel Tank Sumps
Begin by carefully inserting the Fass fuel tank sumps into the fuel tank openings. Ensure the sumps are fully seated and make good contact with the bottom of the tank to maximize fuel draw. Use a sealant, as recommended by Fass, around the sump flange to create a watertight seal and prevent fuel leaks.
Secure the sumps with the provided hardware, tightening the bolts evenly to avoid warping the flange. Double-check that the sump strainer is clear of debris before connecting the fuel lines. Proper sump installation is crucial for ensuring a consistent fuel supply to the Fass pump, especially during low fuel levels. Verify a secure fit before moving to the next step.
Connecting Fuel Lines to the Fass Pump
Attach the fuel lines from the tank sumps to the corresponding inlets on the Fass pump, ensuring a secure and leak-proof connection. Use fuel-rated hose clamps to reinforce the fittings. Identify the supply and return lines correctly; typically, the supply line is larger in diameter.
Tighten all connections to the manufacturer’s specifications, avoiding over-tightening which can damage the fittings. Before proceeding, visually inspect all fuel line connections for proper seating and clamp placement. A secure fuel line connection is vital to prevent fuel leaks and maintain optimal pump performance. Double-check everything before moving forward.

Fass Pump and Motor Installation
Securely mount the Fass pump and motor assembly to the designated location, ensuring proper alignment and vibration isolation for optimal performance and longevity.
Mounting the Fass Pump
Begin by selecting a suitable mounting location for the Fass pump, typically on the frame rail or within the engine compartment, ensuring adequate clearance and accessibility. Utilize the provided mounting bracket and hardware, carefully aligning it with the pre-drilled holes on the pump and vehicle chassis.
Secure the bracket using appropriate-sized bolts and washers, tightening them to the manufacturer’s specified torque to prevent loosening during operation. Employ vibration-dampening materials, such as rubber isolators, between the pump and mounting surface to minimize noise and extend component life.
Double-check the pump’s orientation to ensure proper fuel flow direction and avoid any interference with surrounding components. A stable and secure mounting is crucial for preventing fuel leaks and maintaining consistent performance.
Wiring the Fass Pump Motor
Begin by disconnecting the negative battery terminal to prevent accidental shorts during the wiring process. Identify the Fass pump motor’s power wires – typically red for positive and black for negative. Connect the positive wire to a switched 12V source, ensuring it activates only with the ignition on.
Connect the negative wire directly to a clean, solid chassis ground point, utilizing a ring terminal and appropriate bolt size. Avoid grounding to painted surfaces. Use properly sized wiring (refer to Fass documentation) and secure all connections with crimp connectors or solder for reliable conductivity.
Protect the wiring with loom or conduit to prevent chafing and damage. Verify all connections before reconnecting the battery and testing the system.
Grounding the System
Proper grounding is crucial for the Fass system’s reliable operation and to prevent electrical interference. Locate a clean, unpainted metal surface on the vehicle’s chassis, as close to the Fass pump as possible. Use a heavy-gauge (minimum 10 AWG) grounding cable and a ring terminal to create a secure connection.
Ensure the grounding point is free of rust and corrosion; sanding may be necessary for optimal contact. Connect the grounding cable directly to the chassis, avoiding any body panels or components that may not provide a consistent ground.
Double-check the connection for tightness and conductivity. A poor ground can lead to erratic pump performance or even damage to the system’s electrical components.

Fuel Filter and Water Separator Installation
Install the primary fuel filter and water separator according to the Fass system’s instructions, ensuring proper orientation for optimal filtration and water removal.
Installing the Primary Fuel Filter
Begin by carefully unpacking the primary fuel filter, inspecting it for any shipping damage. Locate the designated mounting bracket provided within the Fass system kit; this is typically positioned near the Fass pump itself for easy access and efficient filtration. Securely attach the filter to the bracket using the supplied hardware, ensuring a snug fit to prevent vibrations during operation.
Next, connect the fuel inlet line from the Fass pump to the filter’s inlet port, utilizing the appropriate fittings and clamps to guarantee a leak-proof seal. Then, connect the fuel outlet line from the filter to the subsequent component in the fuel delivery system. Double-check all connections, tightening them adequately but avoiding over-tightening, which could damage the fittings or filter housing. Proper installation is crucial for maintaining optimal fuel flow and preventing contamination.
Installing the Water Separator
The water separator is a critical component, protecting your 5.9 Cummins from damaging moisture. Begin by identifying the designated mounting location, usually near the primary fuel filter within the Fass system. Securely mount the separator using the provided bracket and hardware, ensuring it’s stable and vibration-resistant.
Connect the fuel line exiting the primary filter to the inlet port of the water separator, utilizing appropriate fittings and clamps for a leak-proof connection. Subsequently, connect the outlet port of the separator to the fuel line leading towards the injection pump. Remember to observe the correct flow direction indicated on the separator housing. Regularly draining accumulated water is vital for maintaining optimal fuel system performance and preventing engine issues.
Filter Maintenance Schedule
Consistent filter maintenance is paramount for the longevity and efficiency of your Fass system. The primary fuel filter should be inspected every 5,000 miles, and replaced every 10,000 miles, or sooner depending on fuel quality. The water separator requires more frequent attention; drain accumulated water every 500-1,000 miles, especially during periods of high humidity or questionable fuel sources.
Regularly check for any signs of filter restriction, such as reduced fuel flow or decreased engine performance. Keep a maintenance log to track filter changes and water draining intervals. Utilizing genuine Fass replacement filters ensures optimal filtration and system compatibility. Ignoring these maintenance steps can lead to fuel contamination, injector damage, and ultimately, engine failure.

Connecting Fass System to the Engine
Proper fuel line routing and secure connections are vital for optimal performance. Ensure lines avoid heat sources and moving parts, preventing damage and leaks.
Fuel Line Routing to the Injection Pump
Carefully route the fuel supply line from the Fass system to the injection pump, ensuring a smooth path free from kinks or sharp bends. Utilize factory mounting points whenever possible to secure the line and prevent chafing against engine components. Maintain adequate clearance from exhaust manifolds, turbocharger housings, and any moving parts to avoid heat damage or potential fuel leaks.
Employ rubber fuel line protectors or heat shielding in areas prone to high temperatures. Secure the line with fuel line clamps at regular intervals, especially near connections and bends. Double-check that the line doesn’t experience excessive stress during engine movement. A properly routed fuel line ensures consistent fuel delivery and prevents potential issues during operation, maximizing the benefits of the Fass system.
Return Line Installation
The fuel return line is crucial for maintaining proper fuel pressure and system efficiency. Connect the return line from the injection pump back to the Fass system’s return port, ensuring a secure and leak-proof connection. Utilize fuel-resistant hose clamps to prevent fuel seepage. Route the return line separately from the supply line, avoiding close proximity to high-temperature components.
Proper return line installation prevents fuel vapor lock and ensures consistent fuel delivery. Avoid sharp bends or kinks in the return line, as these can restrict fuel flow. Secure the line with appropriate mounting brackets to prevent sagging or chafing. Verify the return line’s integrity after installation, checking for any signs of leaks or damage. A correctly installed return line is vital for optimal Fass system performance.
Checking for Fuel Leaks
Thoroughly inspect all fuel line connections, fittings, and the Fass pump itself for any signs of fuel leakage after installation. Start the engine and allow it to run for several minutes, carefully observing all connections. Pay close attention to the areas around the fuel tank sump, pump mounting, filter housing, and injection pump connection.
Use a flashlight to aid in visual inspection, and gently feel around connections for any wetness. If any leaks are detected, immediately shut off the engine and address the issue. Tighten connections, replace damaged fittings, or re-seat hose clamps as needed. A fuel leak poses a significant fire hazard, so meticulous leak checking is paramount for safe operation. Confirm a completely dry system before extended use.

Post-Installation Checks and Priming
After installation, prime the Fass system to remove air bubbles, ensuring consistent fuel delivery and optimal performance for your 5.9 Cummins engine.
Priming the Fuel System
Priming is crucial after installing the Fass system to eliminate air trapped within the fuel lines and pump. Begin by ensuring the fuel tank contains an adequate supply of diesel. Turn the ignition key to the “on” position, but do not start the engine. This activates the Fass pump, initiating the priming process.
Listen carefully for the pump to cycle and build pressure. This may take several cycles, especially after a completely dry installation. Some Fass systems feature a prime button; utilize this if equipped, following the manufacturer’s instructions.
Monitor for any fuel leaks around connections during priming. If leaks are detected, immediately shut off the system and address the issue. Once the pump consistently runs and fuel is observed flowing towards the injection pump, proceed to the next step. A fully primed system is essential for a smooth and reliable start-up.
Checking Fuel Pressure
Post-priming, verifying fuel pressure is vital to confirm the Fass system operates correctly. Locate the designated fuel pressure test port, typically found on the Fass pump or a nearby fuel line. Attach a compatible fuel pressure gauge, ensuring a secure and leak-free connection.
With the engine running, observe the gauge reading. The ideal fuel pressure for a 5.9 Cummins will vary slightly depending on specific engine modifications, but generally falls within the range of 10-15 PSI at idle and increases with engine RPM.
Compare the reading to the manufacturer’s specifications for your Fass system and engine. Low pressure indicates potential issues like a clogged filter, air leaks, or a failing pump. High pressure could suggest a restriction in the fuel lines. Address any discrepancies before prolonged operation.
Initial Engine Start-Up and Monitoring
After priming and verifying fuel pressure, proceed with the initial engine start-up. Turn the ignition key and allow the engine to crank; it may take slightly longer than usual to start as the system fully pressurizes. Once running, closely monitor the engine for any unusual noises, vibrations, or smoke.
Pay particular attention to the fuel pressure gauge during the first few minutes of operation. Ensure it remains stable within the specified range. Inspect all fuel line connections and the Fass pump itself for any signs of leaks.
Allow the engine to idle for a period, gradually increasing RPMs to observe performance. A smooth idle and responsive acceleration indicate a successful installation. Continue monitoring for at least 30 minutes, checking for any developing issues.

Troubleshooting Common Issues
Addressing problems like no fuel delivery, low pressure, or leaks post-installation requires systematic checks of wiring, connections, and the Fass pump itself.
No Fuel Delivery
If the Fass system isn’t delivering fuel, begin by verifying the power supply to the pump motor. Check the wiring connections, fuses, and the relay responsible for powering the Fass pump. Ensure the ground connection is secure and free from corrosion, as a poor ground can prevent proper operation. Next, inspect the fuel lines for any kinks or obstructions that might be blocking fuel flow from the tank to the pump.
Confirm the fuel tank isn’t empty and the fuel shut-off valve (if equipped) is open. Listen for the pump motor running; if it’s silent, further electrical diagnosis is needed. If the motor runs but no fuel is delivered, the pump itself may be faulty and require replacement or professional inspection. Finally, double-check the priming procedure was correctly followed.
Low Fuel Pressure
Experiencing low fuel pressure after Fass system installation indicates a potential restriction or component malfunction. First, inspect the primary fuel filter and water separator for excessive contamination; a clogged filter drastically reduces flow. Verify the Fass pump is receiving adequate voltage – low voltage results in reduced pump output. Examine the fuel lines for any kinks, collapses, or restrictions that could impede fuel delivery to the injection pump.
Check for air leaks in the fuel lines, particularly at connections. Air ingestion lowers system pressure. Confirm the Fass pump is correctly configured for your engine’s fuel pressure requirements. If the issue persists, the Fass pump itself may be failing and require testing or replacement. Accurate fuel pressure testing is crucial for diagnosis.
Fuel Leaks After Installation
Post-installation fuel leaks demand immediate attention to prevent fire hazards and fuel loss. Thoroughly inspect all fuel line connections – fittings, clamps, and the pump itself – for tightness. Ensure proper sealing surfaces are clean and undamaged before reconnecting lines. Check the Fass fuel tank sump installation; improper sealing can cause leaks at the tank. Examine the fuel filter housing and water separator for any cracks or loose fittings.
Pay close attention to the injection pump connection, verifying a secure and leak-free seal. A small leak can quickly escalate, so address it promptly. Use fuel-resistant sealant on threaded connections if necessary. After repairs, run the engine briefly and re-inspect all areas for leaks.






































































