EPA-AA-TEB-81-20
Exhaust Emissions from High-Mileage,
Catalyst-Equipped Passenger Cars
by
Gary T. Jones
July 1981
Test and Evaluation Branch
Emission Control Technology Division
Motor Vehicle Emission Laboratory
U.S. Environmental Protection Agency
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Abstract
This report consolidates results from a number of emission testing
programs on in-use passenger cars. Vehicles from the 1975 through 1981
model years were involved. The purpose of this effort was to examine the
effect of "high mileage" on levels of exhaust emissions. The emission
levels from the vehicles involved were examined from four basic views:
1) "As received" results of the top 15% (by odometer) versus similar
results from the bottom 15% and 85%; 2) "as received" results of vehicles
with over 50,000 miles versus those with under 50,000; 3) the effects of
restorative maintenance on high mileage vehicles; and 4) the effects of
catalyst replacement on high mileage vehicles.
The results show that the high mileage vehicles exhibit higher average HC
and CO emissions than the lower mileage vehicles. The higher emission
levels appear to be due to an increased rate of maladjustments,
disablements and defective parts. It was also found that on the average,
catalytic converters remain active beyond a vehicle's statutory "useful
life" of 50,000 miles and that restorative maintenance is an effective
method to reduce average emission levels. Even further reductions were
possible, especially in HC, through replacement of the catalytic unit.
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Background
Federal Regulations which pertain to light duty vehicle (passenger car)
emissions define "the useful life" of a vehicle as 5 years or 50,000
miles, whichever occurs first. EPA surveillance studies of passenger
cars have demonstrated that even low-mileage, relatively new vehicles can
exhibit poor average emission performance when compared to applicable
standards (Reference 1). When this finding is combined with the fact
that many catalyst equipped vehicles have now exceeded the 50,000 miles
of their "useful life", it is clear that an assessment of these vehicles
must be made to evaluate their impact on air quality. This report
collects and presents the data from a number of programs in which high
mileage vehicles were tested.
Program Design
The data from a number of programs were consolidated and categorized Into
four groups. Table 1 is a listing of the programs from which these data
were gathered. Two of these data groups represent "as-received" results
only. These two groups use the same data base, but are subjected to
different analyses. The remaining two groups show both as-received
results and the effect of maintenance actions on the emission levels of
high mileage vehicles.
Table 1
Program Title
FY 75 Emission Factors
FY77 Emission Factors
FY79 Emission Factors
FY80 Emission Factors
Restorative Maintenance Testing
of High Mileage Vehicles at
High Altitude
Restorative Maintenance and
Catalyst Replacement on High
Mileage Passenger Cars
California Air Resources Board
High Mileage Catalyst Vehicle
Surveillance Test Program
A Study of Exhaust Emissions from
1975-1979 Model Year Passenger
Cars in Los Angeles
Sites '
Chicago, St. Louis, Houston, Denver,
Los Angeles, Washington, D.C., Phoenix
Chicago, St. Louis, Houston, Denver,
Washington, D.C., Phoenix
St. Louis, Houston, Denver, Washing-
ton, D.C., Phoenix, Los Angeles
San Antonio, Denver, Los Angeles
Denver
St. Louis
Los Angeles
Los Angeles
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Data from the FY75, FY77, FY79, and FY80 Emission Factor programs were
utilized for the two "as received" analyses. The first was in a format
of comparing the emissions from the top 15% (by odometer reading) of the
vehicles against the remaining 85%. Results from the bottom 15% were
also addressed in some cases. The 15% figure was chosen arbitrarily to
secure a reasonable sample size while still allowing a wide difference in
average odometer readings. The second method was to divide the vehicles
into two categories by a mileage cutpoint: odometer reading over 50,000
miles versus odometer readings under 50,000 miles. Because of the
different standards these vehicles were designed to meet, the data is
displayed as an average of the "percent of standards". This allows the
data to be grouped together for direct comparison. This method is
utilized in Figures 2, 3, 4, 6, 7 and 8. Shown in Table 2 is a listing
of the Federal Standards which apply to these vehicles.
Table 2 - Exhaust Emission Standards for Passenger Cars (grams/mile)
Federal
HC
CO
NOx
California-
HC CO NOx
1975
1976
1977
1978
1979
1980
1981
1.5
1.5
1.5
1.5
1.5
0.41
0.41
15 3.1
15 3.1
15 2.0
15 2.0
15 2.0
7.0 2.0
3.4(a) l.O(b)
0.9
0.9
0.41
0.41
0.41
0.41(c)
A 0.41(c)
B 0.41(c)
9.0
9.0
9.0
9.0
9.0
9.0
3.4
7.0
2.0
2.0
1.5
1.5
1.5
l.O(d)
l.O(d)
0.7
(a) Waiver up to 7.0 gm/mi possible.
(b) Waiver up to 1.5 gm/mi possible for diesel or innovative technology.
(c) .39 gm/mi standard for hydrocarbons other than methane if methane is
actually measured.
(d) 1.5 gm/mi allowed with 100,000 mile durability.
Note: For the 1981 model year, manufacturers may choose options A or B
separately for their gasoline and diesel product lines in California.
The option chosen in 1981 must be retained for the 1982 model year.
The third group of data dealt with the effects of maintenance on emission
levels. This phase of the high-mileage testing incorporated the same
basic philosophy as earlier Restorative Maintenance (RM) Programs, i.e.,
testing in as-received condition followed by successive stages of
maintenance and retesting until the vehicle either meets its applicable
standards or receives a major tune-up with replacement of any defective
emission-related components (except the catalyst).
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The fourth and final data group examined was restorative maintenance with
catalyst replacement. The catalyst replacement was performed after the
final test in the standard RM procedure. This allowed a direct
comparison of catalyst efficiency.
Discussion of Results
The first group of data utilizes the results from the FY75, FY77, and
FY79 Emission Factors programs. The vehicles were sorted by model year,
and each model year was divided into three categories on the basis of
odometer reading. The first category consisted of the top 15% (by
odometer) of the vehicles and the second and third consisted of the
bottom 15% and 85%. Although this method results in decreasing
differences as the model years progress, there is still a substantial
spread in the average odometer reading. Figure 1 displays this trend
along with the number of vehicles tested in each category. Overall, the
average odometer was 42,400 for the top 15%, 17,700 for the bottom 85%
and 7200 for the bottom 15%. Because of many very small differences
between the bottom 15% and the bottom 85%, the results from bottom 15%
are not displayed graphically, but are discussed in the narrative.
Figures 2, 3, and 4 display the average HC, CO, and NOx emission levels
for the top 15% and bottom 85% by model year. As shown in Figure 2,
every model year, with the exception of 1980, displayed higher average HC
levels on the high mileage vehicles than on the vehicles with lower
mileage. One explanation for the unexpected results in the 1980 model
year is that the average odometer for the bottom 85% was only 4100
miles. Thus, some "green engine effect" may still be evident. The small
sample sizes may also have an effect. On an overall basis, the average
HC of the high mileage group was 160% of standard, the 85% group averaged
120% of the standard and the bottom 15% averaged 96% of the standard.
Figure 3 displays average CO. In each model year, the CO level was
higher for the higher mileage vehicles. Overall, the average CO was 220%
of standard for the high mileage vehicles, 160% of standard for the 85%
group and 140% of the standard for the bottom 15%. Figure 4 shows no
clear trend for the average NOx emissions. On an overall basis, there
does not appear to be a significant difference in average NOx between the
high and low mileage vehicles. A reason for this is that EGR problems
which may cause higher NOx values are offset by problems which result in
richer mixtures and, thus, supress formation of NOx.
This method of grouping was also applied to a sample that contained only
three-way catalyst vehicles. This sample consisted of 428 late model
vehicles in which there was little difference in the average odometer of
the bottom 15% and the bottom 85%. For this reason, only the top 15% and
the bottom 85% were compared. Listed in Table 3 are the "percent of
standards" results for these vehicles. The clear trend toward higher
emissions with higher mileage does not appear as evident here as it was
with the earlier systems.
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Table 3
Vehicles Equipped with 3-Way Catalysts
Model
Year
1978
1979
1980
1981
N Average Odometer
—Percent of Standard—
HC
Top 15%
Bottom 85%
7
35
Top 15% 26
Bottom 85% 143
Top 15%
Bottom 85%
12
65
Top 15% 23
Bottom 85% 117
Overall Top 15% 68
Bottom 85% 360
35384
17158
20419
8181
22006
8899
10702
4486
18953
7983
98
166
165
134
187
117
100
110
140
126
C_0
77
80
74
90
168
116
213
217
138
135
NOx
89
69
89
73
66
74
64
55
76
67
As shown, there are many inconsistences present in the model year
breakdown. On an overall basis, average emissions were slightly higher
in the top 15%.
The second group of results used the same data base as the first group.
However, instead of breaking down each model year into a percentile
grouping, a division point of 50,000 miles was used. This reduced the
number of model years because of the lack of any 1979 or newer vehicles
with over 50,000 miles in the data base. Figure 5 provides information
on the average odometer and the number of vehicles in each category. The
overall average odometer reading for the high mileage group was 62,200
miles while the average for the lower mileage vehicles was 23,200. In
each model year, average HC from the high mileage group exceeded that of
the low mileage vehicles (Figure 6). The overall average HC for the high
mileage vehicles was twice their standards. The average HC for the lower
mileage vehicles was 30% over their standards. Figure 7 displays the
average CO results of these vehicles. The 1978 model year group showed
the only unexpected results with slightly lower CO levels for the high
mileage group which contained only 9 cars. Overall, the high mileage
vehicles displayed an average CO level that was 250% of standard while
the low mileage vehicles displayed 180% of standard. As in the 15-85-15
data group, NOx did not display a clear trend.. In fact, it was an
identical 92% of standard for the overall average on both the high and
low mileage groups (Figure 8). Although it appears the overall average
should be different, the sample sizes of the groups with largest apparent
differences were relatively small.
The third group of data consisted of 133 high-mileage vehicles (average
odometer: 66,500) that underwent RM testing in St. Louis, Denver and Los
Angeles (Reference 2, 3, 4, 5). The majority of the vehicles were 1975
and 1976 models although a few 1977 models were included. The collective
results from these programs are shown in Figure 9. As in other RM
programs on vehicles with lower mileage, substantial improvements in
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emission levels were displayed after maintenance. However, only average
NOx was reduced below its standard. When compared to lower mileage
vehicles tested in other RM programs, the percentage reductions in the
emission levels appear similar although the final levels achieved were
not as low. These results are further confirmed by an earlier
Restorative Maintenance retesting program in the Detroit area
(Reference 6) in which thirteen 1975 model year vehicles received three
RM testing sequences over a two year period. The time interval for the
second and third tests were approximately twelve months and eighteen
months after the first test. The average odometer for each test point
was 9,900 (first test), 27,000 (second test), and 36,000 (third test).
The results from this program show deterioration in the average emission
levels of the retested vehicles in both their "as-received" and
"tuned-up" condition. Restorative Maintenance reduced the levels in the
second and third tests to close to the lowest levels of the first test
point. However, as the mileage increased on these vehicles, the average
HC and CO emission levels of the "tuned-up" vehicles never quite achieved
the levels of the preceding tests. Between the first and last test
(approximately 26,000 miles) the average "tuned-up" HC and CO increased
29% and 53% respectively.
No significant findings were obtained upon sorting the 133 car group by
manufacturer. The highest "as-received" HC was achieved by the Ford as
227% of the standard. The highest CO was 311% of standards achieved by
GM vehicles. The highest NOx was 199% of standard achieved by the
Chrysler vehicle average. Chrysler achieved the lowest as-received HC
and CO values (137% and 188%, respectively). As a group, imported
vehicles displayed the lowest as-received NOx value (101% of standard).
After undergoing maintenance, vehicles from all manufacturers displayed
decreases in each of the regulated pollutants. However, on the average,
none of the manufacturer groups passed their standards for all three.
The fourth and final group of data consisted of twenty-one 1975 and 1976
model year vehicles (average odometer: 87,000 miles) that underwent
restorative maintenance procedures in St. Louis and Denver (Reference 7,
and 8). After the final test in the standard RM procedure, the catalyst
was replaced with a new unit and the vehicle was retested.
Figure 10 displays the emission reductions which occurred during the
different phases of this testing. As expected, a drop in the emission
levels occurred after the major tune-up and component replacement were
performed, although only NOx was reduced to below its standard. After
replacing the catalyst, HC dropped 43% and CO dropped 14%. This brought
average HC below its standard while CO was still above. The new catalyst
obviously had an impact on reducing the emission levels of these
vehicles. However, the replacement catalysts were new and had not been
conditioned in any way. The efficiency of these fresh units would likely
decrease slightly and level off after some mileage accumulation.
An additional area of evaluation involved eight vehicles tested in St.
Louis that had an average odometer of 104,000 miles. This step consisted
of replacing the old catalyst with a plain section of pipe (with
restrictions to duplicate the back pressure). The test performed after
these actions showed evidence of the old catalyst's activity because of
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the emission increases witnessed Average HC was up 87%, average CO was
up 66%, and average NOx remained virtually unchanged. This indicates
that the converters displayed catalytic activity well beyond their
"useful life". When the new catalysts were installed on these eight
vehicles, average HC and CO emission levels fell below the best levels
achieved with the old catalysts. This implies that although the old
units were still active, they were not as efficient as the new units.
Cause Analysis
The data presented has established a definite correlation between higher
mileage and increased emissions. Two possible reasons behind the
increases are a higher rate of defective parts and/or an increase in the
number of maladjustments and disablements. Upon examination of the data
from the underhood inspection forms, it was determined that both of these
factors were predominant. On the 15-85 vehicle group, it was revealed
that 92% of the high mileage vehicles were maladjusted and/or disabled
compared to 80% of the lower mileage vehicles. The rate of defective
parts was 25% for the high mileage vehicles versus 10% for the low
mileage vehicles. The higher- rate of defective parts is probably due to
greater deterioration caused by the increased usage factors. Shown in
Table 3 are the pass-fail rates of the individual control systems. In
each case, the high mileage group displayed higher failure rates than the
lower mileage vehicles. This data suggests that as mileage increases, so
does the rate of maladjustments, disablements, and defective parts. The
ability to reduce the emission levels of these vehicles through
restorative maintenance was clearly shown in the RM programs mentioned
earlier.
Table 3
System Inspection Failure Rates*
System Bottom 85% Top 15%
Induction 17 30
Fuel 75 88
Choke 42 55
Ignition 33 48
Air Pump 3 22
EGR 8 19
PCV 11 18
Evap. 4 . 11
Exhaust 0 2
*Note: A maladjustment/disablement and/or a defective part are the
criteria for failing a system. Numbers are expressed as a percentage of
system failures on vehicles equipped with the subject system.
Conclusions
The results of the above analysis show that the higher mileage vehicles
had significantly higher average HC and CO emissions "as-received" than
similar vehicles with lower mileage. NOx emission levels were
approximately the same. The higher emission levels on the high mileage
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vehicles appear to be due to a higher rate of maladjustment/disablement
actions and defective parts.
Restorative maintenance was effective in reducing the average emission
levels on the high mileage vehicles. However, only average NOx was
reduced to below its standard. Catalyst replacement was effective in
further reducing emission levels after standard RM procedures. Even
though the new catalysts displayed an improvement over the old catalysts,
the original units were still reasonably effective beyond their defined
"useful life". Overall, the results of these programs display the
durability of emission control systems and the ability of high mileage
vehicles to respond favorably to proper maintenance.
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References
1. An Evaluation of Restorative Maintenance on Exhaust Emissions
from In-Use Automobiles, J.T. White, SAE Paper 780082,
March, 1978.
2. Evaluation of Restorative Maintenance and Catalyst Replacement
on Exhaust Emissions from Eight Very High Mileage Passenger Cars
in St. Louis, G.T. Jones, Report #79-10, June, 1979.
3. A Study of Exhaust Emissions from 1975-1979 Model Year Passenger
Cars in Los Angeles, Lawrence Moore and Donald C. Unger, Jr.,
EPA-460/3-79-004, July, 1979.
4. Restorative Maintenance Testing of High Mileage Vehicles at High
Altitude, Automotive Testing Laboratories, Inc., Work Effort
No. 3, Contract No. 68-03-2612, August, 1978.
5. Final Report of the High Mileage Catalyst Vehicle Surveillance
Test Program, California Air Resources Board, MS-80-002,
December, 1979.
6. Evaluation of Restorative Maintenance Retesting of Passenger
Cars in Detroit, G.T. Jones, Report #79-5, January, 1979.
7. Op. Cit. #4
8. Op. Cit. #2
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Figure 9: Restorative Maintenance on 133
1975,1976 and.1977 High Mileage Vehicles
Average Odometer: 66,500
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Figure 10: Restorative Maintenance and Catalyst
Replacement on 21 1975 and 1976 High MileageVehicles
Average Odometer: 87,000
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------- |