environmental facts
REMOVAL OF EMISSION CONTROLS
The Environmental Protection Agency has made a study
to evaluate the feasibility of improving fuel economy on
emission-controlled cars by reversing or disconnecting
emission control features on the engines.
Late in 1973, the advent of the fuel shortage created
extensive public interest in whether the fuel economy of
cars subject to emission controls could be improved by
eliminating such controls. The EPA made public its technical
judgment that any mass program to remove emission controls
from cars would most likely result in no net fuel economy
gain, and might even result in a fuel economy loss.
To check out its technical judgment, the EPA, during
December and January, ran a test'program on this question.
Ten late-model cars (1973/74 models) were obtained for this
experiment. EPA engineers tuned up most of these cars to
obtain baseline emissions and fuel economy values; some cars
were not initially tuned up but were baseline tested in as-
received condition. EPA engineers then made all feasible
adjustments and disconnections that did not require the use
of redesigned carburetor or distributor components (which
are not realistically available to the service industry or
to EPA) for the purpose of maximizing fuel economy. Emissions
and fuel economy were then measured on each car, and each
car put back to manufacturers' specifications.
These tuned-up cars were then taken to service stations
and garages with a request that the emission control systems
be removed. In most cases the service mechanics did not
know that they were participating in an EPA study. After
being worked on by the independent service industry, the
cars were returned to the EPA laboratory, and the emissions
and fuel economy were again measured.
In three cases, the cars were delivered to the service
industry in as-received condition, to see if materially
different results would be obtained. A total of 13 garage
tampering episodes were evaluated with the ten cars; some
cars were used more than once in the program.
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In general terms, this test program found that highly-
skilled emission control technicians who are equipped with
the best tools available (like the EPA technicians who worked
on these cars), were able to improve the fuel economy of
the cars in most cases. The increases found ranged from a
low of 2.2% to a high of 17.8%, with the average increase
being 7%. Emissions of all regulated pollutants increased
substantially in most of these cases.
When worked on by service garages of various types, in
most cases the cars showed fuel economy"1osses; only one out
of the 13 cars showed a significant fuel economy improvement,
while three showed • negligible improvements. The range of
results was from a loss of 15.5% to a gain of 9.9%; the average
1oss for these cars was 3.5%. Again, emissions increased
greatly.
The numerical values cited above cannot be represented
as valid for the entire car population on the road today,
for the following reasons:
(1) The test cars were all 1973 and 1974 models,
which are the most stringently controlled cars
on the road today. Thus, if competently modified,
these cars would show the greatest fuel economy
gains, and older cars would have lower fuel economy
gains;
(2) The sample of 13 tampering episodes on 10 cars
was too small to permit reliable quanti tative
extrapolation to the vehicle population as a
whole. However, the study does identify the
di recti on of the fuel economy changes likely
to be experienced at the hands of highly skilled
emission control specialists, and at the hands
of ordinary spurce industry personnel.
From the data in this test program," as supplemented by
extensive other data, available from other EPA and industry
tests, onie can generalize that on the average the motorist
could avoid a fuel economy loss of about 6% through annual
tune-ups; in other words, about the same gain in fuel economy
can be achieved through keeping a .car in proper tune as was
experienced when experts defeated the emission controls.
It is the EPA's view that this study- confirms its
earlier technical conclusion on the impracticability of
significantly improving fuel economy of cars in the field
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by attempting to remove emission controls. It is especially
interesting that two cars in this test program were modified
by a large specialty garage that widely advertises its
emission control removal service; in both cases their attempt
to improve fuel economy was not successful.
In the interest of both fuel economy and clean air,
the EPA urges motorists to keep their cars in proper tune;
such action stands a much higher chance of improving fuel
economy of cars than does an effort to remove emission controls
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^WASHINGTON, D.C. 20460
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