Knock, Knock.  Fuel System Calling.

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There's probably nothing more critical to maximum fuel performance and engine longevity than clean, uncontaminated fuel. Without regular fuel system maintenance and high-quality fuel filtration, you may face engine downtime as well as costly repairs.

If you're having problems with equipment knocking, vibrating excessively, lacking in power, smoking, operating erratically, losing fuel, or not starting at all, it may be because you're giving too little attention to fuel system maintenance.

It's important to understand why fuel systems should be so high on your maintenance priority list. Diesel engines have evolved dramatically over recent decades to deliver higher power, better efficiency and greater reliability. Fuel systems are precision-machined to close tolerances, and even a little dirt in the fuel or from the outside environment can do severe damage.

At the source

Fuel injection component suppliers recommend fuel entering the injection system meet certain quality levels, yet studies have indicated that more than half of the fuel sold today does not meet ISO fuel-cleanliness standards.

Even before the fuel reaches your supplier and you fill up, fuel sits in tanks at the refinery, unused for perhaps months or even years, and is already starting to degrade.

Several years ago, changing emissions regulations and increasing fuel costs led to the creation of ultra-low sulfur diesel (ULSD) fuel and biodiesel blends. Both of these create additional maintenance challenges for fuel systems and make finer filtration a critical engine requirement.

You're not alone in having to deal with these issues: They're knocking at the doors of diesel equipment operators around the world. Here are some basic fuel system maintenance guidelines drawn from a variety of authoritative sources, including equipment and fuel system manufacturers and machinery service providers.

Avoid contamination

Fuel systems include the fuel pumps and injectors, transfer pumps, filters, governors, timing devices and fuel lines. Water and dirt can destroy these components, which is why avoiding contamination is vital to maintaining engine uptime, maximizing engine power and minimizing future maintenance costs.

Water in the fuel tank may result from machine heating and cooling during normal operation or daily and seasonal temperature changes. Condensation inside the tank may occur when the temperature drops while the equipment is not operating – either while a job is in progress, overnight or on weekends.

One of the easiest ways to avoid condensation is to fill up fuel tanks at the end of each day – that helps drive out any moist air in the tank. Make it a regular practice to drain water and sediment accumulated at the bottom of the tank about 10 minutes after refueling, and before beginning to operate equipment each day.

Some fuel tanks use supply pipes that allow water and sediment to settle below the end of the fuel supply pipe, but most have a valve on the bottom of the tank for draining water and sediment. After draining, be sure to properly close the drain valve to prevent air from entering the system and hindering performance.

Out with dirt

Dirt and debris cause the most damage to fuel systems. Avoiding problems from these abrasive contaminants starts with a practice as simple as always replacing the nozzle back on the refueling pump instead of letting it fall on the ground.

It is more important than ever to ensure that the cap and filler neck area are cleaned periodically and that both the vent tube and fuel tank caps are tightly sealed after each refueling. Whenever possible, further reduce the chance of introducing dirt and dust by changing filters or making repairs indoors.

If you have your own refueling tanks, it's a good idea to clean them periodically and change their filters, too. Draining water and sediment from the storage tank weekly or whenever it is refilled helps prevent water or sediment from being pumped into the engine fuel tank.

Although the internal baffles in bulk tanks should help trap sediment, if you move your tank for any reason, allow adequate time for the sediment to settle before filling up your equipment.

Regular care pays off

The rewards of being disciplined about maintenance are many: optimal fuel atomization, improved engine performance, lower fuel consumption, and reduced fuel system component wear. Equipment experts estimate that contaminants cause more than 85 percent of fuel system failures and can reduce engine life by up to 50 percent.

When debris interferes with the sliding movements of inner and outer valves, nozzle needles and seats, and command piston sliding portions, wear is accelerated. Dirt and dust are particularly harmful at the interface between the injector barrel and the plunger, and on the control valves.

One of the first signs of dirt in the system may be loss of engine power at higher speeds or heavier loads. It's essential to replace both the primary and secondary fuel filters regularly. The primary fuel filter is a very fine screen upstream of the fuel pump. The secondary filter, downstream of the fuel pump, catches contaminants before they go into the injection pump. Depending on the equipment, some systems have one or both filters.

Avoid introducing dust when changing the main filter by waiting to fill the filter element with fuel until filter installation is done. Don't forget to check the O-ring to ensure proper fit. Then proceed to fuel the new filter with the priming pump.

Conversely, fill the pre-fuel filter cartridge with fuel before installing it. Make sure the cap is attached to the new filter cartridge, then pour the fuel into the cartridge itself (not through the center hole). Discard the cap once the cartridge is filled, apply a thin layer of engine oil to the cartridge packing surface before installing it into the filter holder. Once the packing surface comes in contact with the sealing surface of the holder, tighten the cartridge only one-half to three-quarters turn.

Stay on schedule

To avoid diminished engine performance and accelerated component wear, stick to a regular fuel system maintenance schedule. Always follow manufacturer guidelines using mileage, fuel consumption, service hours or calendar time to determine necessary maintenance intervals.

The sidebar lists general recommendations for fuel system maintenance. Check to ensure they are part of your current maintenance schedule. Note that equipment used in severe operating conditions may require more frequent maintenance.


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