Diesel Tech readers are always
trying to get the most performance out of their trucks. As technology
has improved over the years and decades, more and more information
has become available about how to tweak and refit a truck to get
better fuel mileage, more power and consistent stability from a
One area that has received a lot of
attention over the years is the effect of air/vapor and other fuel
contaminants. A leader in this industry is FASS, which stands for
Fuel Air Separation System, and the engineers and other minds at this
company seek to minimize the negative effects of air on your truck's
fuel system, to improve fuel mileage save your injectors,
reduce engine noise, improve throttle response and improve
other areas of performance.
Brad Ekstam represents FASS, and has
been working on diesel engines since as early as 1991.
"I was working on this out of my
garage back then," Ekstam said.
As the FASS system was not developed
until 2003, at this time Ekstam was developing a similar fuel system.
"We had a Cummins 444 engine that was
operating inconsistently," he explained. "Sometimes it'd run real
good, sometimes it wouldn't, and when it wouldn't, it'd fall flat on
its face, the clatter was louder and the performance was much worse."
As the Cummins 444 was supposed to be
the engine of its time for semi trucks, the truck was taken into
Cummins for these issues and warranty work.
"Cummins kept checking for loose
fittings, loose lines and leaks," Ekstam said. "The downtime was
killing us, but eventually the shops told use they were looking for
air in the fuel."
That was the breakthrough they were
looking for. Eckstam and his coworkers took this information and
applied it to the knowledge that when a suction side fuel filter is
removed it is hardly ever full of fuel. This told them they going to
always have this problem with conventional filter systems.
Fortunately, a call to the Cummins Technical and Warranty Department
would open a gold mine of information through a guy named Harold
Webb supplied them with a service topic
written in 1965, on the subject of air in fuel.
"I used to be able to quote this word
for word," Ekstam said.
The service topic explained that the
source of vapor is fuel itself.
"Like water, fuel contains a certain
amount of dissolved air," the service topic read. "Depending on
fuel temperature, pressure on the fuel, specific gravity and the
amount of aeration which the fuel has been subject to." This
information told Eckstam that diesel engines have an inherent problem
when it comes to fuel delivery in a real world environment. Fuel
starvation is air and/or vapor in fuel
These many factors make the process of
separating air and vapor from fuel a very difficult one, and a work
that has been in progress for years.
One problem FASS has faced in dealing
with this issue is that the test conditions for manufacturers'
engines are not exactly real-world. For example, in a test
environment, a fuel tank may be suspended 15-25 feet above the engine
being tested, a far cry from the actual setup of the average diesel
truck. These unrealistic conditions allow manufacturers to get great
performance results, which are then published, leading people to
believe there is no need for further changes to their truck's system.
Positive Flow vs. Vacuum
The boiling point of liquid, in this
case diesel fuel, is directly related to the specific gravity
(vacuum) which it is subjected to. As fuel is subjected to any kind
of vacuum, vapor will be produced. As fuel is subjected to various
degrees of specific gravity, vacuum vapors will be produced in
various amounts and engine performance deteriorates as a result.
"For example, a dirty fuel filter
vacuum, increases the vapor being produced," Ekstam explained.
An engine performs best with clean fuel
filters, and as they restrict little by little, engine performance
deteriorates little by little. Once the filter reaches a point of
restriction to where the engine's maintenance guide indicates
changing, or when you decide the lack of performance is intolerable,
you'll change the filter, gaining back the lost performance.
Even with a clean filter flow is
restricted, everyone understands this.
"Did you know that every 90-degree
angle of fuel line fitting is worth about 13 feet of fuel line
restriction?" Ekstam said.
This is why Ekstam suggests you should
be using mandrel bent fittings especially when the FASS system is not
being incorporated into your application. A 90-degree or "T"
fitting introduces what is referred to as a liquid eddy current,
which creates a restriction while introducing more entrained air and
vapor. When the inside diameter is doubled, the flow is quadrupled.
Manufactures have reduced the amount of air and vapor by simply
enlarging the size of fuel lines along with fuel filters.
Stationary vs. Agitated
Fuel agitation is another major cause
of air in fuel. This is one reason why a diesel engine performs
better after the truck has been sitting for some time.
It is easy to notice how much smoother,
stronger and quieter an engine feels at the start of a drive compared
to other times when the engine has been running for hours upon hours.
Studies from FASS have shown the amount of entrained air in fuel
after 1.5 hours of traveling is equivalent to the vapor being
produced from a filter with 11.5 inches of vacuum/restriction. Most
engine manufacturers don't want to experience more than approximately
7 inches of restriction in a worst-case scenario.
Air and vapor steal lubricating
properties of fuel to the injection system. Fuel creates a barrier
between the metal surfaces, like oil creates a barrier between the
connecting rods and the crank shaft. Whenever there is a lack of
lubrication, galling and scoring will occur from metal-to-metal
contact. Some metal-to-metal contact will completely seize the
operation of that component.
"Have you ever heard of a hung
plunger?" Ekstam asks. "Lack of lubrication is the major cause of
A lot of people just buy the FASS
filtration system for filtering dirt and water, but they're starting
to learn the importance of air. Some models of diesel truck seem to
go through injectors one right after another, but after installing
the FASS system, they discover that in addition to improved
performance, they almost never have to replace their injectors.
"You never know where you're going to
be when that injector goes, so making that last longer is a big
deal," Ekstam said.
FASS is working hard to convey their
message to the diesel truck industry, and what drives them is their
belief that their product is superior and always improving.
"At one time our product was loud,
because we didn't care much about sound coming off of semis,"
Ekstam remembered. "But now we're much, much quieter for consumer
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