Question:How can I tell if my fuel filter needs to be
replaced?
Answer:The only way to tell for sure is to remove the
filter and blow through it. If there's little resistance, the
filter is still okay and does not need to be replaced. But if
there's more than minimal resistance, the filter is dirty and
should be replaced.
CAUTION: Gasoline is poisonous, does not taste very good and
may burn sensitive lips. So don't hold the filter to your mouth
to blow through it. Instead, attach a short piece of clean rubber
hose to the filter and then blow through the hose to test the
filter.
FILTER PROBLEMS
A completely plugged fuel filter will stop your engine cold
by choking off the flow of fuel to the carburetor or injectors.
The engine may not start, or it may start, then stall and die.
Some filters have a spring-loaded bypass, however, that allows
fuel to bypass the filter element if it becomes clogged. Fuel
continues to flow, but it may carry dirt to the carburetor or injectors,
which can create additional problems.
A partially restricted filter will usually pass enough fuel
to keep the engine running at idle or low speed, but may starve
the engine for fuel at higher speeds or loads. So your engine
may run fine putting around town, but sputter and lack power when
you try to drive at highway speeds or pass someone.
TANK FILTER
Located inside the fuel tank is a screen or mesh sock that
acts like a prefilter to keep big pieces of dirt and rust from
being drawn into the fuel pickup tube or tank-mounted electric
fuel pump. If the screen becomes clogged with debris, it can
have the same effect as a plugged or dirty fuel filter. Therefore,
if you've been experiencing a fuel starvation problem and have
replaced the fuel filter -- and it didn't help -- the screen in
the tank is probably the culprit. To clean or replace it, the
fuel tank usually has to be removed.
WARNING: The fuel tank must be drained prior to removal.
The fuel must be stored in a sealed "approved" container.
The battery should also be disconnected to prevent any accidental
sparks from an in-tank electric fuel pump connection from igniting
the vapors. Do not smoke when working on the fuel tank, filter
or fuel lines, and keep all other sources of ignition away (electric
heaters, pilot lights, etc.) from the work area.
FILTER REPLACEMENT
Replacing the fuel filter periodically (every year or so)
for preventative maintenance can reduce the risk of filter-related
driveability problems. Most vehicle manufacturers, however, no
longer specify a replacement interval for the fuel filter. Or,
if they do it's some incredibly long interval like once every
five years or 50,000 miles. Many mechanics feel this is unrealistic.
Waiting that long to change the filter is asking for trouble,
especially if you drive on gravel or dirt roads, buy the cheapest
gas you can find from "cut-rate" stations, use gas with
alcohol in it, or your vehicle is more than six or seven years
old and may have rust in the tank.
The fuel filter on carbureted engines is usually located at
the inlet fitting of the carburetor, or an "in-line"
filter is used between the fuel pump and carburetor.
When replacing a filter that screws into the inlet fitting
on the carburetor, be careful not to overtighten the filter.
The threads in the carburetor are relatively soft and can be easily
stripped. But also make sure the filter is snug so that it doesn't
leak. It's okay to apply some gasket sealer to the filter threads
to assure a leak-free connection. But do not use RTV silicone
sealer (which gasoline dissolves) or teflon tape (pieces of which
can flake loose and end up in the carburetor).
When replacing an in-line filter, most filters come with two
new rubber hoses that go on either side of the filter. Use them.
Don't reuse the old hoses because rubber hoses deteriorate over
time and can leak or shed small flakes or rubber that can end
up in the filter or carburetor. Also, make sure the hose clamps
are properly positioned and tight.
NOTE: Most in-line filters have an arrow showing the direction
fuel should flow through the filter. Install the filter so the
arrow points toward the carburetor.
FUEL INJECTION FILTERS
Fuel filters on fuel injected engines are usually larger and
have a finer filter element than those on carbureted engines.
Consequently, they are usually more expensive.
The filter may be located anywhere between the fuel tank and
injector fuel supply rail or throttle body. On many cars, light
trucks and minivans, the filter is located underneath the vehicle
along a frame rail. On some, the filter is part of the electric
fuel pump assembly inside the fuel tank! Refer to a shop manual
for your fuel filter's location.
CAUTION: Fuel injected engines usually have a lot of residual
pressure in the fuel line, even when a vehicle has sat overnight.
So either follow the manufacturer's recommended procedure for
relieving pressure in the line prior to removing the filter (applying
vacuum to the fuel pressure regulator manifold fitting, or cranking
the engine with the ignition disabled), or wrap a rag around the
hose connections and slowly loosen them.
If the filter has an arrow indicating the direction of flow,
it should be installed with the arrow pointing toward the engine
and away from the fuel tank.
If the filter is located inside the tank, the tank will probably
have to be removed. Follow the same precautions as previously
described for replacing a plugged pickup screen.
