Fuel Filters And Frequency Cycles

On most import vehicles, the three components with the highest manufacturing tolerances are ABS brake modulators, direct injection high-pressure fuel pumps and fuel injectors. All of these components are at the mercy of the fluids that circulate inside their respective systems. While the brake system is closed, a fuel system will pump thousands of gallons of gasoline in the first 100,000 miles.

Filtering out dirt and debris from the gasoline is essential to both the life of the fuel system and engine. Even a small speck of dirt, the size of the width of a human hair, can impair the spray pattern of a fuel injector or damage the surfaces inside a fuel pump. Fuel filters and screens inside injectors and pumps prevent damage from occurring.  

You may have noticed that some late-model Asian and European imports now lack a fuel filter between the pump and fuel rail. In theory, many imports should not need an inline fuel filter because of internal and external factors. 

One of the internal factors is plastic fuel tanks. By not having metal fuel tanks, corrosion inside the tank is eliminated. But it does not mean tanks are impervious to debris entering the tank from the filler neck. The other internal factor is that manufacturers are doing more filtration before the fuel enters the pump. Externally, underground fuel tanks have been improved to prevent internal corrosion and leaks. In the late 1980s, the EPA started to mandate better tanks to prevent ground water contamination. Also, modern gas pumps filter the fuel before pumping it into the tank. 

The new filtration strategy is to trap contaminates before the fuel pump pressurizes the fuel. Older socks or strainers were designed to catch contaminates between 50-100 microns in diameter. Forty microns is equivilant to the size of a human hair. Newer pre-pump strainers or socks can now capture smaller debris and more of it.

If a vehicle has a fuel filter, replace the filter after the pump has been replaced. It sounds simple, but this is often forgotten. The old filter can restrict flow and make the new pump work harder. Restrictions caused by a clogged filter makes for a hotter running pump because most modern systems use a pulse-width modulated voltage to the pump. If the engine management system is not seeing enough fuel pressure at the rail or the fuel trim is too lean, the computer will increase the frequency and duty cycle to the pump to increase fuel pressure. 

Courtesy of Brake & Front End.


Identifying And Fixing Heavy Duty Filter Issues

Today’s heavy-duty engines have evolved to incorporate modern technology and adhere to emissions regulations—which means their components have had to evolve with them. For technicians, this means that when an engine problem comes up, it’s not so simple to determine the root cause.

Say, for instance, you think there’s an issue with a filter; first you need to determine whether that’s true by figuring out which filter is behind the issue, and then you need to take the necessary steps to fix the issue. Tomorrow’s Technician reached out to Edward Covington, director of quality at WIX Filters, to talk us through identifying and addressing these issues.

When a filter-related concern is suspected, Covington says that the first step is to “consider the indicators: engine computer codes, visible leak of filtered fluids, fluid analysis reports, poor engine performance, fluid color or condition or visible exhaust gas emissions.”

“It’s important to note that filters remove contaminants,” he adds. “As this happens, the restriction across the filter increases. This is normal, but if the contaminant load is higher than previous service intervals, filters can reach loading or termination pressure more quickly. A restricted filter may indicate a change in how the engine is operating, a change in the operating conditions, duty cycle of the equipment or vehicle, or an overdue service interval.”

The next step is to identify the specific problem and whether it’s being caused by the air, oil or fuel filter—or none of the above.

Different problems crop up with different types of filters. Covington identified the following common issues with each:

  • Air filters may become clogged or restricted from higher concentrations of airborne dust. In extreme circumstances, water ingestion by an air filter heavily loaded with dust can create a mud cake, further increasing restriction. Built up snow or freezing moisture on an air filter can create higher air flow restriction until the ice is melted and subsequent water drained from the filter.
  • Fuel filters can clog from microbiological growth or gelation in fuel storage tanks due to colder-than-normal fuel temperatures.
  • Fuel water separator units can create a computer code to drain water. Older models without a water level sensor need regular draining, and more often, with higher concentrations of water in the service fuel. For off-road fuel storage tanks, monitoring the amount of water in the fuel is necessary to stop it from draining into the engine.
  • Oil filters can prematurely plug from combustion byproducts if the engine load significantly increases, EGR system imbalances or coolant passage clogs in the oil cooler, which could result in high oil temperature during operation.

Once you determine the type of filter causing the problem, Covington notes that there are a couple of questions you will need to answer before you proceed:

  • Is the filter being used recommended by the manufacturer for that specific engine and application?
  • Are the correct fluids being used? For engine lubricating oil, verify base oil type, viscosity and API rating. For coolant, verify type and chemistry. For fuel, verify gasoline, diesel or bio fuel.
  • Also, what is the duty cycle of the truck? Is the truck often used in harsh or severe conditions? If so, this will accelerate the service interval, which will need to be noted once the truck goes back on the road.

“Most lubricating oil filters require new seals or o-rings and specific installation torque values,” he notes. “Reuse of single-use seals or use of an alternate filter seal can create a leak path. Air filter differential pressure sensors need to be reset with each filter change. Engines equipped with intelligent oil life calculators need to be reset at oil and filter changes as well. These calculators rely on correct base oil, viscosity and rating, and a filter rated for the service interval and duty cycle to accurately inform when service is due.”

Lastly, for circumstances in which the filter is believed to have caused engine damage, be sure to follow the warranty submission requirements from the filter manufacturer; opening or altering the filter to self-diagnose the problem could void the warranty.