As the drive to lower emissions and improve fuel efficiency continues, proper maintenance of the fuel injection system is essential for optimal fleet engine performance. The fuel injection system is responsible for delivering fuel to the cylinders of an engine. To operate correctly, the timing and amount of fuel used during the injection process must always be precise and controlled.

When a fuel injection system issue arises, it can lead to poor vehicle performance. To avoid any inconveniences, fleets can educate themselves on some of the latest technologies, signs that indicate when there is an issue and the equipment needed to address it, as well as how to maintain fuel injection systems.  

Latest technologies

Cylinder deactivation, or CDA, is a technology used to reduce fuel consumption and vehicle emissions, especially at low speeds and/or low loads.

CDA disables cylinders (can be one or more) by deactivating the intake and/or exhaust valves, closing them off completely. As a result, the reduction in the number of cylinders firing reduces fuel demand to improve fuel economy, and the remaining active cylinders will operate at a higher temperature. This design can also help to improve the efficiency of the aftertreatment system by allowing the system to reach the optimum operating temperature for a passive diesel particulate filter (DPF) regeneration.

All diesel engines require a fuel injection system because of how fuel and air mix to initiate the combustion process. Common rail fuel injection is the type of fuel injection system found in all modern diesel engines. Fuel is dispersed to each injector using a high-pressure rail where the electronically controlled injectors can allow multiple injections at any pressure at any time. Higher injection pressures allow for better fuel atomization which produces more power and fewer emissions.

With high injection pressure and control over injectors, the common rail injection system offers reduced emissions, noise, and vibrations, as well as increased fuel efficiency and engine performance.

Manufacturers have taken the common rail fuel injection system technology even further by making modifications to increase its performance.

According to Dave Needham, diesel product engineering director at Delphi Technologies, the company’s F2 common rail system includes low static injector leakage and dynamic leakage features. The company is currently working to develop the F3 generation that will feature a DFI 21 injector. The DFI 21 injector will be fitted with a 1mm diameter nozzle control valve to reduce leakage and allow for higher injection pressures. The F3 system will also offer embedded closed-loop control electronics that will monitor the operation of each injector and adjust performance in real-time.

Volvo Trucks’ common rail system is completely contained under the valve cover and consists of three pumping and three non-pumping injectors, says John Moore, product marketing manager at heavy duty original equipment manufacturer Volvo Trucks North America. The three pumping injectors are directly connected to a rocker arm that rides a double lobe cam, allowing for two pumping sequences for each injector during every full rotation of the camshaft.

This design not only optimizes the efficiency of the pumping injectors due to less surface area on pumping surfaces but also lowers the clamping load on the injector from the rocker. Pumping twice per revolution of the cam enables a smaller diameter pumping piston to be used to generate a maximum rail pressure of 35,000 psi. It also delivers the volume of fuel necessary under a full load. The smaller piston diameter requires less force from the rockers to generate the same pressure required for a larger diameter piston.

Volvo’s common rail system also reduces weight by not running high-pressure lines up the side of the block from a transfer pump to the common rail. The pumping injectors are directly connected to the rail and can directly inject fuel into the cylinder with the fuel under pressure from the common rail.

Determining when there’s an issue

There are several different ways to verify whether there is an issue with the fuel injection system, some more visual than others. One such way is to track fuel economy.

Fleets that monitor each of their vehicle’s fuel consumption and mileage will notice when there is a fluctuation in fuel economy.

“Say you have a fuel injector that is leaking or delivering more fuel than it should be, you would track that if you were tracking fuel economy,” says Mike Cleary, owner and ASE master heavy truck technician of Cleary Automotive. Cleary also manages and teaches courses for Automotive Technical Support Services (ATSS), a training organization offering technician training for drivability and electronics diagnostics.

Another indicator of a fuel injection issue is checking the air-fuel ratio by using a scan tool. If the air-fuel ratio is running too rich or too lean – meaning there is too much fuel or too little fuel, respectively – this can cause the combustion process to be less efficient.

“If ‘X’ amount of air goes in the engine, the fuel is supposed to match that depending on the load that is being delivered,” says Barry Hoyland, owner of Vehicle Service Solutions of California (VSSCA), a repair center that specializes in emissions and diagnostic services. “If there’s an air-to-fuel ratio problem, it’s likely due to the fuel is not being delivered properly. That’s an indicator that there’s a problem with the injection.”

Hoyland also provides consulting services for fleets and government agencies to improve their operational efficiencies.

Visible and audible signs that indicate fuel injection system issues include an illuminated malfunction indicator lamp (MIL) sometimes referred to as a “check engine” light; rough or loud vehicle idling; hard starting, engine misfires, visible smoke, acceleration issues, and/or loss of performance. Additionally, increased emissions, engine oil dilution, or fuel in the engine crankcase would also indicate a fuel injection system issue.

When one or more of these signs are noticed, it is important to inform the fleet’s technician to properly check and diagnosis the issue.

In late-model trucks with aftertreatment systems, if the issue is too severe the truck will derate and eventually shut down, Hoyland notes.

Equipment needed to diagnose

Technicians may use a variety of tools to diagnose issues with the fuel injection system, depending upon the symptoms the vehicle is showing and the model year of the vehicle.

Vehicles built before 2000 generally don’t have extensive vehicle computer technology, whereas models manufactured after 2000 do. These newer vehicles allow technicians to use a modern-day scan tool, VSSCA’s Hoyland says.

In addition to a scan tool, to test fuel injection issues technicians may need an oscilloscope, digital voltmeter, and thermal imaging camera, as well as exhaust gas sampling and fuel pressure and volume testing.

A scan tool with bidirectional control allows technicians to perform a cylinder balance test, but a cylinder cutout test would be most useful, Hoyland says. These tests allow the technician to disable, or cut out, a cylinder while the engine is running at a specified rpm to find the one that has a fault.

“Some scan tools will actually give you a cylinder contribution all the time so you can see how each cylinder is operating,” Hoyland says. “[The scan tool] does that by measuring crankshaft speed. If you have one cylinder that is not contributing as much, then the crankshaft actually slows down after that cylinder is fired, so you can see what cylinder is misfiring based on crankshaft revolution.”

A thermal imaging camera enables the technician to look at the exhaust manifold and each cylinder at the exhaust port. The tool measures the temperature of the exhaust coming out. If a cylinder is being over- or under-fueled, the thermal imaging camera will indicate a difference in temperature.

In addition to equipment, using the vehicle’s information such as wiring and repair diagrams as well as fuel pressure requirements is also important to review, Hoyland adds. This information is available through the engine and/or truck manufacturers, as well as many repair information sources.

Maintaining fuel injection systems

“Maintaining the [fuel injection] system can result in reduced operating costs,” says Simon Lynch, diesel aftermarket sales manager at Delphi Technologies. “Also, preventive maintenance reduces unexpected downtime that can result in dissatisfied customers.”

It is important for fleets to adhere to best practices when maintaining fuel injection systems. Not only to follow a standard routine but to keep each vehicle running at peak performance.

Both Hoyland and Cleary agree that the two most important aspects to proper fuel injection system maintenance are using clean filters and quality diesel fuel.

“Change the primary and secondary fuel filter with a premium filter every time the oil is changed,” Volvo Trucks’ Moore recommends. “Replace the fuel tank ventilation filter every two years and run overhead-valve adjustments at proper intervals.”

For diesel fuel, make sure the fuel is from quality sources, and ensure there are no contaminants or moisture in the fuel.

If using biodiesel, fleets should inspect the tanks and filters for algae contamination regularly, Moore adds.  

“The major cause of failure on [fuel injection] systems, is lack of maintenance or some kind of self-induced failure where [technicians] were changing the fuel filter and debris entered the system,” Cleary says.

When handling any kind of fuel injection system, Cleary advises technicians “need to, as best as you can, make sure you’re working in a clean environment because these systems are very, very intolerant of debris.”

Hoyland also suggests completing fuel injection system service and repairs when a fuel injector or fuel pump needs to be replaced to avoid contaminating the injectors.

“If [what you’re replacing has] got a supply line to it, make sure that there’s no rust or anything going through the fuel lines that can contaminate the new injectors,” he says. “It’s doing a complete repair to make sure that you’re not going to continue a problem after a specific repair.”

Another best practice is to train new drivers on proper techniques for refueling and the proper use of fuel additives.

Fuel additives should be used at the ratio recommended by the manufacturer. Keep in mind there may be differences in additives for diesel and biodiesel as well.

“Every now and then I hear of a driver that accidentally adds DEF solution into the diesel, which really wreaks havoc on the fuel injectors,” Moore says.