Question:My mechanic says my injectors are dirty and
need to be cleaned. What does that mean?
Answer:"Dirty" is actually a misnomer. Rarely
are injectors clogged with dirt. Rather, they are usually clogged
or restricted by a buildup of fuel varnish deposits. This reduces
the amount of fuel that the injector sprays, which in turn may
cause the engine to run lean and misfire, hesitate or stall.
A fuel injector is nothing more than spray nozzle. With mechanical
injectors, a spring loaded valve allows fuel to squirt out of
the nozzle when line pressure overcomes spring tension that holds
the valve shut. With electronic injectors, a spring-loaded solenoid
pulls open a pintle valve or ball type valve when the injector
is energized by the computer. This allows the pressurized fuel
in the fuel rail to flow through the injector and squirt out the
nozzle.
Injectors come in a variety of styles. Early Bosch style
injectors have a pintle valve and are the ones most prone to clogging.
In 1989, General Motors introduced its new "Multec"
style injectors which have a ball valve design and are claimed
to be more resistant to clogging. Other injectors have a disc-valve
design that is also said to resist clogging.
The truth is ANY injector can clog. Nobody's injectors are
immune to this kind of problem, but some are obviously better
than others.
Problems can occur even with a slight buildup of deposits.
Because the injector orifice is so small, it doesn't take much
crud to restrict the flow of fuel or to disrupt the spray pattern.
For good combustion, the injectors must produce a fine cone-shaped
mist of fuel vapor. Wear or deposits in the nozzle can create
"streamers" of liquid fuel that vaporize and burn poorly.
This, in turn, can cause hesitation, emissions and performance
problems.
INJECTOR CLEANING
The cure for a set of clogged injectors is cleaning -- or replacement
if they're too badly clogged to respond to cleaning. Injectors
are expensive to replace. New domestic injectors sell for
to each, with new import injectors fetching to
each. Injectors should only be replaced as a last resort.
If your injectors are clogged, they can be cleaned with pressurized
solvent, or removed for off-car cleaning. There are also fuel
tank additives that claim to clean clogged injectors, but
the cleaning such products do is usually minimal. So save your
money and put it towards a professional cleaning.
There are do-it-yourself on-car injector pressure cleaning
kits that are similar to the equipment professionals use. But
some of these kits can be tricky or even dangerous to use. Our
advice is to let a professional do it.
On-car injector cleaning involves feeding solvent under pressure
into the injector fuel rail or supply line. The concentrated
solvent passes through the injectors and loosens and washes away
the accumulated varnish deposits. The results are usually good,
and make a noticeable difference in idle smoothness, emissions
and fuel economy.
If your injectors are really clogged and fail to respond well
to on-car cleaning, off-car cleaning using special fuel injection
cleaning equipment would be the next logical option. Some of
this equipment is designed to "reverse" flush the injectors
so any debris that's trapped inside the injector or above the
inlet screen will also be removed. Off-car cleaning also allows
a mechanic to observe the spray pattern of the injectors to make
sure there aren't any streamers or problems. Off-car cleaning
is more expensive because of the labor involved to remove the
injectors, but the results are usually better.
KEEPING INJECTORS CLEAN
The best way to minimize or eliminate the need for injector
cleaning is to use a quality brand of gasoline that contains sufficient
detergent to prevent varnish buildup. Most brand name gasolines
today have enough detergent to do this. As a rule, premium grades
usually contain a somewhat higher concentration of cleaners.
You can also use fuel tank additives to keep your injectors
clean. Such products really aren't necessary if you're using quality
gasoline. But if you're buying the cheapest gas you can find,
using an additive might be good insurance.
