EPA-AA-IMS-ST-80-1
Analysis of In-House I/M Testing of a Three-Way Chevrolet
Citation and a Three-Way Dodge Aspen
January, 1980
NOTICE
Technical Reports do not necessarily represent final EPA decisions or posi-
tions. They are intended to present technical analysis of issues using data
which are currently available. The purpose in the release of such reports
is to facilitate the exchange of technical information and to inform the
public of technical developments which may form the basis for a final EPA
decision, position or regulatory action.
Inspection/Maintenance Staff
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air, Noise and Radiation
U.S. Environmental Protection Agency
-------
-2-
I. INTRODUCTION
This report is an analysis of the effectiveness of I/M-type "short tests" in
identifying grossly emitting vehicles. Specifically, this report examines
the question for two vehicles equipped with the technology to be introduced
nationwide in 1981. This technology incorporates a high degree of engine
control through the use of sensors, actuators and an on-board computer, and
allows the simultaneous conversion of HC, CO and NOx in a three-way cata-
lyst. .''
In a testing program performed in-house at the Motor Vehicle Emission Labor-
atory, Ann Arbor, Michigan, a 1980 Chevrolet Citation and a 1979 Dodge Aspen
were selectively disabled to simulate possible in-use vehicle conditions. A
wide range of testing was performed at each condition including FTP testing
and I/M short tests. In this report, the FTP results will be compared to
the results of two .I/M tests to examine their effectiveness in identifying
vehicles with gross FTP emissions. Each vehicle will first be discussed
separately and then an overall comparison will be given. Performance of the
two tests using the recently proposed 207(b) cutpoints will be evaluated
separately in Section IV. Full data sets for the two vehicles can be ob-
tained from the reports referenced at the end of this report.
II. 1980 CHEVROLET CITATION
A. Vehicle Description
The Citation was equipped with a 2.5 liter L-4 engine and the General
Motors "C-4" emission control system. The C-4 system incorporates an
oxygen sensor, digital on-board computer, and a solenoid operated
feedback carburetor. The Citation is equipped with EGR and a single
three-way catalyst for the conversion of HC, CO, and NOx. It is cali-
brated to meet the 1980 California standards of Q.41/9.0/1.0.
B. Analysis
For the Citation, the emissions from seven distinct vehicle conditions
were examined. The I/M tests were performed twice for each condition.
Two baseline test sequences were performed at the beginning and the end
of the test program. Three of the seven vehicle conditions had gross
FTP HC and CO emissions. These were:
I
- Mixture control solenoid disconnected
- Mixture control solenoid disconnected and EGR disconnected.
- Oxygen sensor disconnected and lead short-circuited.
The other vehicle conditions resulted in low FTP HC and CO emissions
and involved disconnecting such things as the coolant temperature
switch, the EGR valve, the closed throttle switch, and the oxygen
sensor (without short-circuiting the lead).
-------
To examine how well the I/M tests could identify the grossly emitting
vehicle conditions, the FTP emissions were plotted against the I/M
test's emissions. For the Citation, these plots can be seen in Figures
1-4. To be a successful screen in identifying gross emitters, while
not falsely identifying clean cars, an I/M test should yield values
which roughly correlate with the FTP emissions. Therefore, for a
successful test, plots such as Figures 1-4 should have a cloud of
points in the lower left hand corner from the "clean" cars and a cloud
of points in the upper right hand corner from the grossly emitting
cars. Conversely, any point in the upper left hand corner (above an
I/M test's cutpoint and below the FTP standard) would represent an
error of commission (i.e. a falsely identified vehicle) and any point
in the lower right hand corner (below the I/M cutpoint and above the
line representing gross FTP emissions) would represent an error of
omission (i.e. a vehicle with high enough FTP emissions to warrant
identification in an I/M program). Vehicles would routinely be tested
for both HC and CO, and failure for either pollutant (i.e. emissions
above a selected cutpoint) would be sufficient to identify the vehicle
as needing maintenance.
As can be seen in Figures 1-4, both the Loaded Two Mode test and the
non-loaded Two Speed Idle test were successful in identifying the gross
emitters. The scatter of points for the two tests are very similar,
the chief difference being that the emissions from the 2500 rpm mode of
the Two Speed Idle test were somewhat lower than all the other modes.
These emissions from the 2500 rpm mode are not normally used as a
criterion for evaluating whether or not a car would pass or fail an I/M
test.
It is also clearly evident that no errors of commission or omission
would result from either test. This is based on cutpoints^of 1% CO and
100 ppm HC and assumes the emissions from the 2500 rpm mode of the Two
Speed Idle test are not essential in determining failure as discussed
above.
III. 1979 DODGE ASPEN
A. Vehicle Description
The Aspen was equipped with a 225 CID engine, EGR, a vacuum operated
feedback carburetor, an oxygen sensor, an on-board computer and a
three-way catalyst for the conversion of HC, CO, and NOx. The Aspen
was also equipped with an oxidation catalyst and an air pump to provide
additional HC and CO control. It was designed to meet the 1979 Cali-
fornia standards of 0.41/9.0/1.5.
B. Analysis
For the Aspen, the emissions from five distinct vehicle conditions were
evaluated as well as two baseline tests at the beginning of the program
and one baseline test at the end of the program. The five vehicle
conditions were:
-------
-4-
- oxygen sensor disconnected
- coolant temperature sensor disconnected
- mixture control vacuum solenoid disconnected
- air injection bypassed
- EGR disconnected
As with the Citation, two sets of I/M tests were run for each condi-
tion. Unlike the Citation, however, none of the conditions had truly
gross FTP HC and CO emissions. Even those conditions which involved a
loss of feedback control did not result in high HC/CO emissions on
either the FTP or the I/M tests. This is due primarily to the addi-
tional oxidation capacity provided by the extra oxidation catalyst in
series with the three-way catalyst. This oxidatioi catalyst is sup-
plied with oxygen by an air pump which leans out the- exhaust stream in
the oxidation catalyst even when a rich mixture is bein,? provided by
the carburetor. Thus, the catalyst is better able to .leal with the
higher levels of HC and CO which would normally result from a loss of
engine feedback control. The only vehicle condition with emissions
significantly above the standard is that with the air pump disconnected
(FTP HC = 1.03 gm/mi, FTP CO = 29.8 gm/mi). This underlines the issue
discussed above, that is, with the air pump disabled and much of the
additional oxidation capacity lost, the Aspen's emission performance
begins to resemble the Citation's more closely.
As with the Citation, the I/M test's emissions were plotted against the
FTP emissions. It is important to note the different scales used on
these plots as opposed to the Citation's plots. Both the I/M emissions
and the FTP emissions have different scales. These plot 5 can be seen
in Figures 5-8.
As can be seen in Figures 5-8, the single vehicle condition with higher
FTP emission levels was essentially separated from the other points.
This is especially true for CO (Figures 5 and 7). It is important to
note, however, that a relatively low I/M cutpoint would have been
needed to identify this car as needing maintenance (approximately .5%
CO). For HC, the FTP emissions for the one higher condition were not
as grossly above standards as for the FTP CO emissions, and the corre-
sponding I/M tests' emission levels were also not as high. As can be
seen in Figures 6 and 8, however, the emission levels at idle were
essentially separate for the one higher point.
As can also be seen in Figures 6 and 8, one point (representing a
disconnected EGR with FTP HC emissions at 0.4 gm/mi and with I/M tests'
emissions of 70 ppm and 90 ppm for the Loaded Two Mode and the Two
Speed Idle respectively), could possibly have caused an error of com-
mission. This would depend of course on the I/M cutpoint used.
One data point for the Aspen was dropped as it was an apparent data
collection error.
-------
-5-
IV. PERFORMANCE OF THE TWO I/M TESTS USING 207(b) CUTPOINTS
A. Description of 207(b) Outpoints
Section 207(b) of the Clean Air Act provides for the establishment of
I/M cutpoints which could be used in warranty claims against the auto
manufacturers. In this portion of the report, the currently proposed
cutpoints (Reference 3) will be applied to the data from the Aspen and
the Citation.
For the Two Speed Idle test, the 207(b) cutpoints are 1.0% CO and 200
ppm HC. The lower of the emission levels from the two idle modes
and/or the emission levels from the 2500 rpm mode can be selected as
the criteria by a state or municipality to determine whether or not a
vehicle passed the test. Thus, the idle emissions alone, the 2500 rpm
emissions alone, or the two combined can be used as a basis for deci-
sion. It is also important to note that if a vehicle fails any section
of the test and for either CO or HC, it fails the whole test.
For the Loaded Two Mode test, the cutpoints are 1.2% CO and 220 ppm HC
for both modes of the test. Here too, a state or municipality can
choose the emissions from either or both of the modes as the basis for
decision, and if a vehicle fails any section of the test for either CO
or HC, it fails the whole test.
B. 1980 Citation
For the Citation, both the Loaded Two Mode test and the Two Speed Idle
test demonstrated perfect performance (i.e. no errors of commission or
errors of omission) using the 207(b) cutpoints in all possible config-
urations of the test criteria. All of the failures were for high CO
levels.
C. 1979 Dodge Aspen
For the Aspen, none of the I/M tests' emissions were above the 207(b)
cutpoints, so there were therefore no errors of commission possible.
The failure rate for correctly identified vehicles was also therefore
zero.
In looking at errors of omission, points to the right of (i.e. above)
the FTP standard in Figures 5-8 must be identified. For the Aspen, the
applicable standards are 0.41/9.0/1.5 for 1979 California vehicles.
Using these standards, three of the eight vehicle conditions could be
called "errors of omission", however in terms of significance, only the
vehicle condition with the disconnected air pump could be termed a
significant error of omission. The other two conditions had FTP emis-
sions only marginally over the standard.
In summary then, analysis of the Aspen's emissions using 207(b) cut-
points is inconclusive, since to properly evaluate the issue, a wider
spread of data would be needed. There were no errors of commission and
there was one significant error of omission.
-------
-6-
V. CONCLUSIONS
Both the Loaded Two Mode and the Two Speed Idle tests demonstrated their
ability to identify the grossly emitting vehicle conditions. This depends
of course on the cutpoints used and what is defined as grossly emitting.
For CO, the issue is clear, and especially so for the grossly emitting
conditions from the Citation. For HC, the issue is clear for the Citation
and somewhat clouded for the Aspen. In general, the results from the Aspen
are of limited value, since the central question involves whether I/M tests
can identify gross emitters or not, and the Aspen had generally very clean
emissions. One thing that can be said for both the Citation and the Aspen
is that the vehicle conditions with low FTP emissions also had low I/M test
emissions, i»e., there were no significant errors of commission. This is
especially true for CO and generally true for HC except for the one ques-
tionable point from the Aspen discussed above.
-------
-7-
References:
1. Evaluation of Applicability of Inspection/Maintenance Tests on a Dodge
Aspen Prototype. August 1979, Thomas J. Penninga, Technology Assessment and
Evaluation Branch, Emission Control Technology Division, OANR, U.S. EPA.
2. Evaluation of Applicability of Inspection/Maintenance Tests on a Chevro-
let Citation. October 1979, Thomas J. Penninga. Technology Assessment and
Evaluation Branch, Emission Control Technology Division, OANR, U.S. EPA.
3. Light Duty Vehicle and Light Duty Truck Emission Performance Warranty;
Short Tests and Standards. December 1979, Inspection/Maintenance Staff,
Emission Control Technology Division, OANR, U.S. EPA.
-------
-8-
Figure 1
CITATION
FTP CO vs. Loaded Two Mode CO
01
13
O
S
o
"$.
H
cd
O
8.0
7.0
6.0
5.0
4.0
3.C.
2.C.
l.C.
25
50
75
+
D
D
D
FTP CO
(gm/mi)
+ =
100
30 mph.
Idle"
B
125
-------
240
220
200
180
160
140
*
0.
CL,
g~ 120
T3
cfl
O
100
80
60
40
20
-9-
Figure 2
CITATION
FTP HC vs. Loaded Two Mode HC
B
B
D
D
0.5
1.0
1.5
FTP HC
(gm/mi)
2.0
30 mph.
Idle
2.5
3.0
-------
-10-
Figure 3
CITATION
FTP CO vs. Two Speed Idle CO
7.0
6.0
8 5.0
M
^N
0) S-'
01
w* 4.0
o
H
3.0
2.0
1.0
0
D
A
A
A
A A
A
0 25 50 75 100 125
FTP CO + = 1st Idle
(gm/mi) A = 2500 rpm
O = 2nd Idle
-------
-11-
Figure 4
CITATION
FTP HC vs. Two Speed Idle HC
240
220
200
180
160
140
0)
H
/-N
0 S
aj p<
0) P.
w ^ 100
80
60
40
20
0
C
-
-
Ifa
D Q
m
A
A
A
A
' -f
^
) 0.5 1.0 1.5 2.0 2.5 3.0
FTP HC + = 1st Idle
(gm/mi) A = 2500 rpm
O = 2nd Idle
-------
-12-
Figure 5
ASPEN
FTP CO vs. Loaded Two Mode CO
J..U
0;9
0.8
0.7
o
u
a) 0.6
-a
s
o
H &5
a ^ 0.5
cu
n)
O
0.4
0.3
0.2
0.1
0
r +
n
a
a
0 5 10 15 20 25 30 35
FTP CO Q = 30 mph
(gm/mi) + = Idle
-------
-13-
Figure 6
ASPEN
FTP HC vs. Loaded Two Mode HC
J.OU
140
120
o 100
a
0)
1
^~\
o S
££
3~ 8°
n)
0
60
40
20
0
-
+
+ +
D 4H- +
° D D
+
Ifc D
i i -i -1 - j i i i i i i
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
FTP HC O = 30 mph
(gm/mi) + = Idle
-------
-14-
Figure 7
ASPEN
FTP CO vs. Two Speed Idle CO
I.U
0.9
0.8
0.7
0.6
o
o
0)
-------
-15-
Figure 8
ASPEN
FTP HC vs. Two Speed Idle HC
J.VJVS
140
120
K 100
0)
'S ^
"O CX
Q) CX
Q)
£ 8°
1
60
40
20
0
D
a
a
EB
D
at*
Bu
+ la 1
A n A
/\
A /\
| i | i ( | | 11 i
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
FTP HC + = 1st Idle
(gin/mi) A = 2500 rpm
O = 2nd Idle
* VS. GOVERNMENT POINTING OFFICE: 1980- 651-112/0168
------- |