The TITAN XD incorporates a robust fuel delivery system to feed the powerful Cummins 5.0L V8 Turbo Diesel engine. Through its two-stage filtering and low-to-high-pressure design, the fuel is clean, highly pressurized, and precisely metered when it reaches the cylinders.

The fuel system components (fuel pumps, fuel lines, fuel rails, injectors) contain high-pressure fuel. To avoid personal injury or fire:

DO NOT LOOSEN ANY FUEL FITTINGSs while the engine is running or the ignition is turned ON.

WAIT AT LEAST 10 MINUTES after shutting down the engine and turning the ignition OFF before loosening any fuel fittings in the fuel system to allow pressure to decrease to a lower level.

WEAR APPROPRIATE EYE PROTECTION and protective equipment as high-pressure fuel spray can penetrate the skin.

FOLLOW ALL WARNINGS AND CAUTIONS in the Electronic Service Manual (ESM) when working with any fuel system components.

Although the high pressure side of the fuel system is designed to not hold pressure following engine shutdown, make sure to wait at least 10 minutes after the engine has shut down to allow pressure to decrease to a lower level before loosening any fittings.

STAGE 1 FUEL FILTER/WATER SEPARATOR & LIFT PUMP

The stage 1 fuel filter, fuel water separator, and electric lift pump are all one assembly that is mounted on the driver’s side frame rail near the fuel tank.

This assembly is part of the low-pressure portion of the fuel system and incorporates a fuel pressure relief valve to prevent overpressure in the system.

The pressure relief valve will open a pre-filter passage at approximately 102 psi, which directs fuel back to the filter inlet.

FUEL FILTER/WATER SEPARATOR

The fuel filter element also acts as a fuel and water separator.

The housing incorporates a drain valve to remove water from the collection container.

An anti-siphon valve is built into the assembly to prevent draining the fuel tank during routine maintenance.

Refer to the Owner’s Manual or the ESM for water draining information.

The water-in-fuel (WIF) sensor sends a signal to turn ON the water-in-fuel warning light when it detects the presence of water in the bottom of the stage 1 fuel filter, indicating that the collection container must be drained.

LIFT PUMP

The lift pump features a check ball to ensure a filter is installed. The fuel filter is equipped with a plastic needle that inserts into the bottom of the lift pump, keeping the check ball from being able to seat against the inlet of the lift pump.

If no fuel filter is installed, the ball will be drawn by the lift pump against the inlet causing the engine to not start.

The electric lift pump runs continuously while the engine is running to ensure a steady supply of fuel to the stage 2 filter and injection system at all times.

Fuel is drawn from the fuel tank, pressurized to between 65 and 101 psi, and then exits to the stage 2 filter.

Within the lift pump is a thermal recirculating valve. At start up, return fuel headed for the fuel tank is diverted back through the stage 1 fuel filter, and then back to the engine (stage 2 fuel filter). Diverting the fuel in this way heats the fuel more quickly, as opposed to allowing it to return and mix with the cold fuel in the fuel tank. Once the fuel temperature reaches approximately 100ºF, the thermal relief valve closes and recirculation is stopped.

STAGE 2 FUEL FILTER

The stage 2 fuel filter, located on the engine, continues the low-pressure part of the fuel system.

The stage 2 fuel filter element features a supply/return seal that keeps the supply fuel, in the upper sections of the filter housing, separated from the return fuel passages in the bottom. If the filter is not installed or seated properly, the engine will not start.

A manifold in the stage 2 fuel filter directs fuel, coming from the lift pump, to the high-pressure pump (injection pump).

Return fuel from the injection pump, injectors, and fuel rails is routed to the stage 2 fuel filter.

The stage 2 filter assembly houses a temperature sensor and a pressure sensor that are used by the ECM for fuel system management.

CONSTANT PRESSURE VALVE

The constant pressure valve is located on the injector return line between the injectors and the stage 2 fuel filter.

The constant pressure valve is a permanent part of the injector return line and is not serviceable separately.

During normal operation, the injectors continuously release fuel into the return lines. This fuel pressure pushes on a check ball inside the constant pressure valve. The pressure in the line increases to the point necessary to move the ball off its seat. At that point (between 160 and 200 psi), fuel will pass through the constant pressure valve and into the stage 2 fuel filter.

At start-up, the constant pressure valve allows fuel to flow in the opposite direction from the stage 2 filter directly up to the low pressure chamber of the injectors. This is done so the injectors will more quickly receive sufficient back pressure to operate efficiently.

INJECTION PUMP (HIGH-PRESSURE PUMP)

The injection pump, located at the front of the engine between the cylinder heads, has two pumping chambers and is chain-driven from the crankshaft.

A high-pressure check valve built into the pump prevents damage from over pressure.

A cascade overflow valve built into the pump regulates fuel supply to the fuel pump actuator, fuel pump lubrication, and fuel return.

A fuel pump actuator mounted on the high-pressure fuel pump at the inlet to the two pumping chambers regulates the volume of fuel that is allowed to enter the pumping chambers. The fuel pump actuator is controlled by a Pulse Width Modulation (PWM) signal from the ECM. Using the fuel pump actuator to regulate the volume of fuel that enters the pumping chambers is one of the controls that the ECM uses to regulate fuel pressure within the high-pressure system.

The high-pressure portion of the fuel system operates between 3,625 and 29,000 psi.

COMMON RAILS AND SUPPLY LINES

After leaving the injection pump, the high-pressure fuel routes through the supply lines to the left and right bank fuel rails on its way to the injectors.

A rail-to-rail fuel supply line directs fuel from the right bank fuel rail to the left bank fuel rail.

The fuel rails act as fuel manifolds accumulating and distributing fuel to each of the injector supply lines.

The high-pressure fuel supply lines are NOT reusable.

If loosened, the fuel line MUST be replaced with a new line.

FUEL RAIL PRESSURE SENSOR

The right bank fuel rail contains a fuel rail pressure sensor that monitors the pressure provided to the fuel rails from the high-pressure fuel pump.

FUEL RAIL PRESSURE RELIEF VALVE

The left bank fuel rail contains a fuel rail pressure relief valve.

The fuel rail pressure relief valve is controlled by a Pulse Width Modulation (PWM) signal from the ECM.

Using the fuel rail pressure relief valve to regulate the fuel pressure in the high-pressure system is one of the controls that the ECM uses to regulate fuel delivered (injected) into the engine.

Bleed off fuel from the fuel rail pressure relief valve is routed to the return manifold in the bottom of the stage 2 fuel filter.

When the engine shuts down and the ignition is turned OFF, the fuel pressure relief valve will open, allowing the fuel pressure inside the rails to depressurize. Before opening any high-pressure components, make sure to wait a minimum of 10 minutes for fuel pressure and temperature to decrease.

NOTE: If the fuel pressure relief valve is replaced, the “Fuel or Timing System Table Reset” MUST be performed using CONSULT-III plus. Refer to the ESM for details on this procedure.

FUEL INJECTOR OPERATION

1 High-pressure fuel is supplied to the high-pressure control chamber of the injector.

2 High-pressure fuel pushes down on the top of the needle and holds the needle closed.

3 The ECM commands injection with an electrical signal to the piezo crystal stack, which opens the control valve.

4 When the control valve is opened, high-pressure at the top of the needle is relieved, allowing high-pressure at the bottom of the needle to overcome the needle spring pressure and inject fuel into the engine; some fuel (excess fuel from the high-pressure chamber) flows into the low pressure chamber.

5 Fuel in the low pressure chamber flows back through the injector drain lines to the constant pressure valve and into the stage 2 fuel filter.

NOTE: If an injector return line is restricted or blocked (such as a pinched return line), the pressure in the low pressure chamber will rise, which may cause damage to the injector. Normal operation pressure in the low pressure chamber is approximately 160-200 psi. The amount of fuel that is injected is controlled by increasing or decreasing the fuel pressure in the high-pressure side of the fuel system, and by injector pulse duration.

Fuel Injector Service Tips

Each injector has an alphanumeric “trim code” that is matched to the cylinder within the ECM from the factory. If an injector is removed, make sure it is reinstalled in the same cylinder. If a new injector is installed, the trim code on the new injector must be matched to the cylinder using CONSULT-III plus.

  • When replacing an injector, an injector removal tool (J-54402) must be used to prevent injector damage.
  • Each injector has a flat sealing washer and a sealing O-ring that are replaced anytime an injector is replaced. Make sure the old sealing washer is not left in the injector bore. Double-stacked or missing sealing washers can cause fuel leaks and possibly affect vehicle performance.
  • Make sure to follow all ESM information when servicing the fuel injectors.

    • DO NOT electrically disconnect an injector while the engine is running, doing so could:

  • Cause electrical shock from injector circuits. (Injectors circuits operate at up to 250 volts and up to 19 amps).
  • Damage the injector. A damaged injector could cause a free flow condition. A free flow condition could cause engine damage and/or physical injury.

FUEL SYSTEM ALERTS AND WARNINGS

WATER-IN-FUEL WARNING LIGHT

  • Displays “dripping water from fuel filter” icon light
  • Indicates that water must be drained from the stage 1 fuel filter.
  • Refer to the Owner’s Manual or the ESM for water draining procedures Low Fuel Pressure warning light
  • Displays “Low Fuel Pressure, Please Service Fuel System”
  • Indicates low fuel pressure has been detected.

The ECM may alter engine performance.

Likely causes:

  • Fuel gelling due to cold ambient climate – winter blend fuels and anti-gelling additives can aid in mitigating low fuel pressure in cold climates.
  • Restricted fuel filters – refer to the ESM for recommended service and repair.

    • Fuel System Priming Procedure

    It is not necessary to vent air from the high-pressure fuel system before starting the engine.

    When the ignition is turned ON, the electric lift pump will run until the fuel system is primed or 90 seconds, whichever comes first.

    PURGE AIR OUT OF THE FUEL SYSTEM AFTER SERVICING THE FUEL SYSTEM, OR AFTER REFILLING A COMPLETELY EMPTY FUEL TANK BY THE FOLLOWING PROCEDURE:

    1. Turn the ignition ON (foot off brake, push ignition twice), and wait for 90 seconds to prime the fuel system. After 90 seconds, crank the engine for a maximum of 30 seconds or until the engine starts. If the engine does not start, repeat this step.
    2. When the engine does start, it may operate erratically and with increased noise levels for a few minutes. This is a normal condition as air is being removed from the system.

    NOTE: It is possible for a warning or indicator light to illuminate due to air entering the fuel system.

    MAINTENANCE INTERVALS

    FUEL-WATER SEPARATOR – CHECK/DRAIN

    NOTE: Water-in-Fuel warning light – Indicates that water must be drained from the stage 1 fuel filter.

    10,000 MILES (16,000 KILOMETERS) OR 12 MONTHS, WHICHEVER COMES FIRST

    STAGE 1 FUEL FILTER – REPLACE

    When installing a new filter, also install a new filter housing O-ring, which is included with the replacement filter element. Apply clean petroleum jelly or white lithium grease on the filter housing O-ring and the inner filter element O-ring before installation.

    After a fuel filter replacement or service, it is possible that air introduced into the system may set DTCs. Be sure to operate the engine until air is purged and then check and clear any DTCs.

    STAGE 2 FUEL FILTER – REPLACE

    Apply clean petroleum jelly or white lithium grease on the O-ring and the inner seal of the filter element before installation. When installing the new filter, insert the filter onto the standpipe first and properly seat it, then screw the cap down. If the O-ring sealing the supply chamber from the return chamber is damaged, performance issues or a no-start condition could occur.

    After a fuel filter replacement or service, it is possible that air introduced into the system may set DTCs. Be sure to operate the engine until air is purged and then check and clear any DTCs.

    20,000 MILES (32,000 KILOMETERS) OR 2 YEARS, WHICHEVER COMES FIRST

    HIGH-PRESSURE FUEL SUPPLY LINES

    Refer to the ESM for recommended maintenance inspection.

    • Clean all fuel fittings, filter housings, and other fuel system components before disassembly. Dirt or contaminants can damage the fuel system.
    • Cap Plug Kit - Fuel System: Whenever components are removed for testing, orifices should be immediately covered with clean care cap plugs.

    Cap Plug Kit - Fuel System (J-54427)