Issue Paper
Technical Feasibility of a 2.0 g/test SHED
Evaporative Emission Standard for Light Duty
Vehicles and Trucks
June 1976
Michael W. Leiferman
Standards Development and Support Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air and Waste Management
U. S. Environmental Protection Agency

-------
Technical Feasibility of a 2.0 g/test SHED Evaporative
Emission Standard for Light Duty Vehicles and Trucks
1. Statement of the Problem
Does the technology exist to meet a SHED evaporative emission
standard of 2.0 g/test for light duty vehicles and trucks?
2. Facts Bearing on the Problem
a.	Some 1974-76 production vehicles have evaporative emission
levels below 2 g/test as measured by the proposed 1978 SHED testing
procedure. Tests on 16 1975-76 2bbl Chevrolet Vegas showed that 10
of these vehicles averaged less than 2 g/test. Tests on a 1974
Plymouth Duster, a 1976 Datsun Pickup, a 1975 Volkswagen with fuel
injection (FI), a 1975 Cadillac with FI, a 1976 Vega with Fl, a
1976 Audi with FI and three Datsuns with FI have also yielded
results of less than 2 g/test. Available test information for
these eight types of vehicles is listed in Table I.
b.	Under EPA Contract No. 68-03-2172, Exxon Research and Engineering
modified the evaporative control systems and measured the evapora-
tive and exhaust emission levels of six vehicles . In the final
modified form, the SHED evaporative emissions, including background,
from each of these six vehicles averaged less than 2 g/test. For
only one of these vehicles was the exhaust emissions of CO or HC
significantly higher in the modified condition than in the stock
condition. The results of these tests are contained in Table II.
c.	Some manufacturer-developed experimental evaporative emission
control systems have given SHED evaporative emission levels, including
background, of less than 2 g/test. These systems and test data are
given in Table III.
d.	Tests have shown that well purged canisters substantially
reduce diurnal emissions. This program was conducted at the EPA
Vehicle Emissions Laboratory and results are shown in Table IV.
e.	Background SHED emissions were determined on 15 1973-75
production vehicles (all at least 90 days old) by Exxon under
Contract No. 68-03-2172. Seven of these vehicles had background
levels of 0.1 g/test or less, and the average value was 0.34 g/test.
These data are presented in Table V.
f.	Variability of the SHED evaporative test was evaluated for a
vehicle near the 2 g/test level in a recent MVMA-F.PA cross-check
test program. Within the five test sites, the standard deviation
ranged from 3% to 12%. The standard deviation of all tests at all
sites was 10%.
Clarke, P. J., "Investigation and Assessment of Light Duty Vehicle
Evaporative Emission Sources and Control," Exxon Research and Engineer
ing, EPA Contract it 68-03-2172, May 1976.

-------
-2-
TABLE I. SHED Evaporative Tests on Production Vehicles


Tested
No. of
Average
Average
Total,
£
Vehicle
Engine
By
Tests
Diurnal, g
Hot Soak,
g Range
Average
'75 Vega
140-2 bbl
ARB
1
0.4
1.5

1.9
'75 Vega
140-2 bbl
ARB
1
0.4
1.1

1.5
'75 Vega
140-2 bbl
ARB
1
0.6
1.2

1.8
'75 Vega
140-2 bbl
ARB
3
0.2
0.9
1.2-1.3
1.2
'75 Vega
140-2 bbl
ARB
1
0.3
0.8

1.1
*75 Vega
140-2 bbl
GM
5
1.37
1.02

2.39
175 Vega
140-2 bbl
GM
2
0.40
1.59

1.99
'75 Vega
140-2 bbl
Exxon
2
0.27
4.48
3.82-5.67
4.75
'75 Vega
140-2 bbl
EPA
7
0.61
0.78
1.15-1.61
1.39
'76 Vega
140-2 bbl
EPA-MVMA
22
0.94
1.06
1.59-2.45
2.00
'76 Vega
140-2 bbl
GM
1
0.80
0.60

1.40
*76 Vega
140-2 bbl
GM
1
0.88
2.87

3.75
17 6 Vega
140-2 bbl
GM
2
1.14
2.01
2.30-3.99
3.15
'76 Vega
140-2 bbl
GM
1
1.35
2.71

4.06
'7 6 Vega
140-2 bbl
GM
13
0.64
1.44

2.08
'76 Vega
140-2 bi?l
GM
5
0.69
1.16

1.85
'76 Vega
121-FI^
GM
1
0.64
0.87

1.51
'74 Ply.
225-1 bbl
Exxon
2
0.47
1.03
1.23-1.76
1.50
Duster







75 Cad.
500-FI
GM
2
0.25
1.07

1.32^2)
2.01
'75 VW
97-FI
Exxon
3
0.67
1.34
1.55-2.61
'75 VW
97-FI
EPA
11
0.83
1.90
2.44-3.42
2.73
'75 VW
97-FI
ARB
1
-
2.90
3.8- 5.8

'75 VW
97-FI
VW
3-5
-
-
—
'76 Audi
97-FI
VW
3-5
-
—
0.8 - 2.4
-
'76 Datsun
]68-FI
Nissan
1
0.51
0.69

1.20
'76 Datsun
168-FI
Nissan
1
0.29
1.06

1.35
'76 Datsun
16S-FI
Nissan
1
0.38
1.13

1.51
'76 Datsun
119-2 bbl
Nissan
1
0.26
1.67

1.93
(1)	FI = Fuel Injected
(2)	Includes a background level of 1.5 grams.

-------
TABLE II. SHED Evaporative Tests on Vehicles Tested Under Contract No. 68-03-2172.

ECS
Evaporative Emissions, g
Exhaust
Emissions
, g/mi^

Condi-
No. of
Average
Average
Total



Vehicle
Engine tion
Tests
Diurnal
H. Soak
Range
Average
HC
CO
NOx
'75 Ford
351-2bbl Stock
2
3.4
3.2
6.2 -7.1
6.7
0.54
6.75
1.62

Modified
2
0.2
1.0
1.2 -1.3
1.2
0.52
4.44
1.87
'75 Pontiac
400-4bbl Stock
2
0.4
7.1
7.2 -7.8
7.5
0.80
6.95
1.31

Modified
3
1.2
0.7
1.6 -2.5
1.9(2!
0.68
4.05
1.36
'74 AMC
232-lbbl Stock
2
0.5
10.3
10.8 -10.8
10.8
1.50
24.5
1.24

Modified
2
0,3
0. 9
1.2 -1.3
1.2
1.51
26.9
1.13
'74 Mazda
80-4bbl Stock
2
0.2
10.4
10.5 -10.7
10.6
2.11
11.7
0.88

Modified
2
0.6
0.9
1.3 -1.8
1.5
1.82
9.90
0.65
'74 Volvo
121-FI Stock
2
4.7
3.2
7.1 -8.7
7.9
0.91
13.3
2.15

Modified
2
0.7
0.4
0.4 -1.7
1.1
1.24
22.6
1.58
'75 Chrysler
440-4bbl Stock
2
5.3
8.6
13.4 -14.6
13.9
2.32
23.2
00

Modified
2
1
0.6
'
1.3
1.-9 -2.0
1.9
1.10
13.3
1.83
^ Average of 2 or more tests
(2)
This data is for an underhood ventilating fan system. A PCV-purged canister system was later
tested on this vehicle and average 1.6 g/test for 2 tests.

-------
-4-
TABLE III. Manufacturer's SHED Evaporative Tests on Experimental
Control Systems.
Vtehicle


No. of
Average Emissions,
g
No. Make
Engine, CID
Carburetor
Tests
Diurnal
Hot Soak
Total
1 Oldsmobile^^
455
4 bbl
1
0.33
1.17
1.50
2 Chevelle(2)
250
1 bbl
1
0.64
1.23
1.87
3 Chrysler(3)
318
2 bbl
1
0.42
1.31
1.78
4 Chrysler^
225
1 bbl
7
0.72
1.05
1. 78
5 Ford(5)
302
-
3
-
-
1.45
6 Ford(5)
400
-

-
-
1.54
7 01dsmobile(6)
455
4 bbl
1
0.85
1.07
1.92
8 01dsmobile(7)
455
4 bbl
1
0.74
0.96
1.70
9 Oldsmobile^^
-
-
1
0.80
0.92
1.72
10 31dsmobile(9)
-
-
2
0.48
1.18
1.66
(1) Dry canister, closed air cleaner snorkel during hot soak and float bowl
vented to canister.
/"?) Vapor purge valve, float bowl vented to canister and internal vent closed.
) 2-way carburetor bowl vent.
v<+) Carburetor bowl vent to canister.
(5)	Bowl vent valve,PCV purged enlarged canister, auxiliary canister, electronic
air cleaner door and new gas cap.
(6)	Proposed production ECS design with manually operated carburetor bowl switch.
(7)	Proposed production ECS design with vacuum operated carburetor bowl switch.
(8)	Experimental V-8 engine with bowl vent and air cleaner door, 1978 prep.
(9)	Experimental V-8 engine with manual bowl vent switch, 1976 prep.
TABLE IV. Effect of Pre-purged Canister on SHED Diurnal
Emissions from 1975 Model Vehicles
Model
Engine, CID
Carburetor
Proposed
Procedure, g
Procedure with
Pre-purged canister, g
Camaro
350
2
bbl
0.92
0.25
Vega
140
2
bbl
0.54
0.35
New Yorker
440
4
bbl
5.1
0.48
Matador
360
4
bbl
4.5
0.85
jrage
1



2.77
0.48

-------
-5-

TABLE V.
SHED Background Measurements
or Production
Vehicles
Vehicle
Background Emissions, g
Year
Make
Model
Cold
Hot
Total
'75
Chrysler
¦New Yorker
0.0
0.1
0.1
'75
Ford
Country Squire
0.0
0.1
0.1
'75
Mercury
Monarch
0.0
0.0
0.0
'75
Chevrolet
Vega
0.0
0.6
0.6
'75
Buick
LeSabre
0.1
0.3
0.4
'75
VW
Beetle
0.7
0.8
1.5*1*
'74
AMC
Hornet
0.0
0.1
0.1
'74
Dodge
Dart
0.0
0.1
0.1
'74
Mercury
Comet
0.0
0.1
0.1
'74
Ford
Pinto
0.0
0.2
0.2
'74
Chevrolet
Nova
0.0
0.1
0.1
74
Oldsmobile
98
0.2
0.3
0.5
'74
Datsun
610
0.1
0.2
0.3
'74
Mazda
RX-4
0.5
1.1
1.6<2)
'74
Volvo
144
0.1
0.1
0.2
'73
Plymouth
Fury III
0.1
0.7
0.8

<3>
Average

0.09
0.25
0.34
(1)	Source tests indicate the emissions are coming from the external enamel
paint.
(2)	Evidence of gasoline spillage in trunk.
(3)	Omitting the 1974 Mazda.

-------
-6-
3. Discussion
a.	Table I indicates that most 1975 Vegas have evaporative emis-
sions of less than 2 g/test. The evaporative control system (ECS)
used on this vehicle is unique in the automotive industry. It uses
the charcoal canister to store carburetor bowl vapors and the
canister purges through a line into the PCV system during off-idle
operation. Since this ECS was highly effective on its first applica-
tion, the successful use of this system on other vehicles looks
very encouraging. There is no technical reason why this basic
purge system cannot be installed on other engines.
, The ECS used on the Plymouth listed in Table I purges the
canister through a line into the carburetor. Since data on only
one of these production vehicles is available, the effectiveness of
this particular engine-ECS combination is not as well established
as that of the Vega. Similarly, there are only limited data on the
carbureted Datsun listed in Table I. The Cadillac, VWs, Audi, 168
Datsuns and 121 Vega in Table I are fuel injected, so induction
system losses are markedly reduced over non-controlled carbureted
engines.
b.	The purpose of Contract No. 68-03-2172 with Exxon Research and
Engineering was to determine the amount of evaporative emissions
from late model production vehicles, the source of these losses,
and the hardware required to minimize these losses. The vehicles
tested were obtained from rental fleets or from private owners.
The Exxon data listed in Table I are from this program. Twenty
vehicles were tested for the specific sources of evaporative losses
and the largest source was found to be the engine air cleaner
during the hot soak. Most of these vapors were emitted through the
snorkel; however, some leaks were found at seams in the air filter
housing and between the housing and the carburetor. These losses
could be prevented by using a vapor tight air filter housing,
fastening the housing securely to the carburetor, equipping the
snorkel with a vapor eight door which would close vhen the engine
is not running or cranking, and venting the carburetor float bowl
to a carbon canister.
The second greatest source of vapor losses found by the
Exxon study was the carburetor during hot soak. Most of these
losses were emitted around the accelerator pump shaft. Some
losses were also detected around throttle shafts. The losses
around the accelerator pump shafts could most simply be prevented
on most carburetors by fastening a vapor tight flexible boot around
the shaft and against the carburetor. Such a device has already
been used on some production carburetors. Another fix would be to
switch from plunger to diaphram type accelerator pumps. These also
are standard on some production carburetors. Leaks around throttle
shafts would probably best be prevented by an improved fitting

-------
-7-
between the throttle shaft and the carburetor wall. Many of the
vehicles tested did not have losses from around the carburetor
throttle shafts. Therefore, preventing these losses on all car-
buretors should present no major problem.
The final source of emissions which contributed a substantial
amount to the total loss from the production vehicles
was the carbon canister. The quantity of emissions from this
source was about equally divided between the diurnal and hot soak
phases. These losses can be prevented by increasing the working
capacity of the canister as previously discussed.
The next step in Exxon's contract was to modify or change the
evaporative systems on 6 of the production vehicles they had tested
and then evaluate the effect of these alterations on evaporative
and exhaust emissions. The final results of these tests were pre-
viously presented in Table II. As shown, the six vehicles selected
represent the four major U.S. vehicle manufacturers and two foreign
manufacturers. Final modifications resulted in an average level,
for each vehicle of below 2.0 g/test, including background. Only
one of the final 13 tests gave an emission of greater than 2.0 g
(the 2.5 g result on the Pontiac).
A listing of the specific modifications and corresponding
emission levels for each vehicle is contained in Attachments 1
through 6 of the Appendix. As listed, several different modi-
fications were evaluated on some of the vehicles. A summary of
these modifications is listed in Table VI. As shown in Table VI,
canister purge into the intake manifold via the PCV line was
installed on three of the vehicles and worked effectively. It was
expected that a PCV purge would also be effective on the Chrysler
and Pontiac, but other types of modifications were used on these
vehicles in order to investigate other types of control systems.
An underhood ventilating fan was used on the Pontiac; however, this
is a more complex solution than a PCV purge system. After the
originally scheduled tests were conducted on the modified vehicles,
the Pontiac was equipped and tested with a PCV purge system (with-
out the ventilating fan). Two evaporative tests gave results of
1.52 g and 1.75 g.
As shown by the vehicle descriptions in Attachment 1 through 6 of
the Appendix, the six vehicles which were modified by Exxon were
representative of popular models sold by major automotive
producers. The engines in the cars produced by the three largest
U.S. manufacturers were all medium or large V-8s, two of which had
four barrel carburetors. Evaporative emissions from large engines
with large carburetors are generally the most difficult to control.
This is because the amount of vapors generated by these vehicles
is large. So the level of control which was achieved by the Exxon
program, should be more easily accomplished on vehicles with smaller
engines. Consequently, results of this study strongly indicate that
essentially all vehicles can be modified to give evaporative emissions
of less than 2.0 g/test.

-------
-8-
TABLE VI. Vehicle Modifications Under Contract No. 68-03-2172.
Vehicle
Modifications
1975 Ford
Canister replacement with PCV purge
Seal-carb. leak
Barrier-snorkel base
Air cleaner leak sealing
Canister bottom cap
1975 Pontiac
Bowl vent to canister
Seal-carb. leak
Canister bottom cap
Air cleaner leak sealing
Fan
1975 Chrysler
Canister replacement
Canister bottom caps
Bowl ven,t to canister
Barrier-snorkel base
Seal-carb. leak
Air cleaner leak sealing
1974 Hornet
Canister replacement with PCV purge
Seal-carb. leak
Bowl vent to canister
Air cleaner sealing
Canister bottom cap
Barrier-snorkel base
1974 Mazda
Bowl vent to canister
Canister with PCV purge
Fan
Canister "bottom cap
1974 Volvo
Canister Replacement
Baffel between tank and muffler

-------
-9-
c. Table III showed results of manufacturer's evaporative tests
on non-production engine-ECS combinations which have given total
evaporative levels of less than 2 g/test. On the Oldsmobiles,
carburetor venting to the canister is part of the production ECS.
The various modifications to these vehicles consisted of closing
the carburetor to canister vent line during engine operation, use
of a dry (well-purged) canister and blocking the air cleaner snorkle
during the hot soak. The dry canister effect can be achieved in
normal vehicle operation by either better purging of the current
canister (assuming its dry capacity is sufficient) or by increasing
the size of the current canister. Trapping vapors in the air
cleaner consists of making the air cleaner essentially vapor-tight
when the engine is not running or cranking. The experimental
system used on the Chevelle (1.87 g/test) does require some changes
to the production carburetor as listed in Table III.
The data on the 225 CID Chrysler Corporation vehicle consisted
of seven tests on one vehicle with various configurations of
carburetor bowl venting to the canister. The average of all seven
tests was 1.78 grams, so it appears that this type of modification
is sufficient to achieve a 2 g/test emission level, ^ata from one
test was reported on a vehicle equipped with a 318 in engine and a
2-way carburetor vent. The result of this test was 1.78 g as
listed in Table III. The engine modification used on this vehicle
was similar to that on the Chevelle listed in the same table. The
2-way carburetor bowl vent consists of a valve which vents the
carburetor bowl to the carburetor throat during engine operation
and to the canister when the engine is not running.
The system used on the Ford vehicles listed in Table III is a ...
system which has already been developed to meet a 6 g/test standard.
Ford supplied test data on many vehicles which were equipped with
this control system. Although most of these vehicles had evaporative
emission levels greater than 2 g/test, the two listed vehicles did
give emission levels below 2.0 g/test on all six tests (three tests
per vehicle).
d. Table IV listed results of tests to determine if the
working capacity of carbon canisters used in production evaporative
systems was sufficient for the diurnal test. The first part of
this experiment consisted of testing the production vehicles according
to the proposed SHED procedure. Then the procedure was repeated,
except that a well purged canister (same size and configuration as
the standard unit) was placed on the vehicle following the cold
soak period and just prior to the diurnal test. As Table IV shows,
the pre-purged canisters lowered the diurnal emissions of all four
vehicles. The amount of this reduction ranged from 0.2 g on the
Vega "to about 4 grams on the New Yorker and Matador. This indicates
that the working capacity of the canisters was not sufficient. As
(2) Ford Motor Company, "Comments in Response to the Notice of Proposed
Rulemaking Published in Fed. Reg. 2022 et. seq., dated Jan. 13, 1976,"
Feb. 27, 1976.

-------
-10-
demonstrated by the above discussed Exxon test program, this capacity
can be increased by either improved purging of the present canister,
use of a large canister or a combination of these two methods.
e.	Table V listed the background emissions for 16 of the 20
vehicles tested by Exxon. Gasoline spills had occurred from an
auxiliary fuel tank in the interior of the first four vehicles
tested, and therefore realistic background data is not available
for those cars. All vehicles were at least 90 days old. From
Table V it does not appear that background emissions were related
to vehicle age. In fact, except for the VW and the Mazda, the
oldest vehicle had the highest background emissions. One-half
of the 1975 vehicles had background levels of 0.1 g or less. From
this data it appears that the variation in background level is
dependent on characteristics of the specific vehicles. Limited testing
for the source of emissions from the VW indicated that it originated
from the exterior of the vehicle and probably from the paint. The
enamel paint used on this vehicle apparently drives slower than the
paint typically used on U.S. manufactured cars.
f.	Attachment 7 in the Appendix lists the results of SHED evapora-
tive emissions on a 1976 Chevrolet Vega. These data are from a
cross-check program in which AMC, Chrysler, EPA, Ford and GM partic-
ipated. At least three tests were conducted at each facility. For
all tests conducted on this vehicle the standard deviation was 0.20
grams or 10% of the mean value. With this combined test-to-test
and lab-to-lab variability of 10%, the maximum mean emission level
a particular vehicle can have in order to be at or below 2.00 g on
a single test at a 90% confidence level is 1.77 grams. Also, in
the certification process, a retest can be requested if a vehicle
fails the first test. For a 90% probability of passing at least one
of two tests, again assuming a standard deviation of 10%, the
vehicle mean is 1.90 g/test.
To compare the variability of these SHED tests with current
exhaust emission variability, results of an exhaust correlation
test between EPA.and Ford are presented in Attachment 8 of the
Appendix. This program consisted of 5 tests at each facility
conducted according to the federal exhaust emission testing proce-
dure. The car used was a 1977 Ford durability vehicle.
As shown by Attachments 7 and 8, the variability-of the SHED
evaporative tests was typical of the variability encountered in
exhaust emission testing. The percent standard deviation for all
evaporative test results is 10%, and the standard deviation for all
exhaust HC, CO, and NOx test results is 14%, 13% and 6% respectively.
Since relatively little experience has been gained with the SHED
evaporative test as compared to the exhaust test, SHED variability
should decrease with improvements and refinements in the procedure.

-------
-11-
g.	The proceeding parts of this discussion have shown that there
are two basic methods of reducing evaporative losses from vehicles.
The first method is reducing the amount of gasoline which evaporates,
and the second method is preventing the gasoline which has evaporated
from entering the atmosphere.
The amount of gasoline which evaporates from a fuel system
is determined mainly by the volume of gasoline and the increase in
temperature of the gasoline. Therefore, techniques for reducing
evaporative losses by the first method are reducing fuel tank size,
reducing carburetor gasoline bowl volume, heat shielding the fuel
tank from exhaust and engine heat, and reducing carburetor tempera-
tures by heat shielding and external cooling (ventilating underhood
area with fans, louvers, etc.). The second method of vapor control
consists of capturing and disposing of gasoline vapors. When the
vehicle is operating, this is accomplished by ducting the vapors
into the engine induction system. However, when the engine is not
operating the vapors must be stored if they are to be disposed of by
the engine. Locations where vapors can be stored are in the
engine crankcase or induction system or in an external container such as
an activated carbon canister. For maximum effectiveness, it is
important that these storage devices do not leak gasoline vapors. As
demonstrated by the previously referenced Exxon study, hydrocarbon
leakage from vapor storage devices (air cleaners and carbon canisters)
was the major source of evaporative emissions.
Most production and experimental vehicle evaporative control
systems consist mainly of the second method of control (capture
and disposal of generated vapors). This method has generally shown
to have greater feasibility and be less expensive than preventing
gasoline vaporization. The particular system which has currently
shown to be most effective is the one used on the Chevrolet Vega.
This system stores both fuel tank and carburetor vapors on activated
carbon. These vapors are subsequently purged into the engine
induction system at a rate which is determined by engine load
(intake manifold vacuum signal). This system, even when used
without closing the internal carburetor bowl vent or sealing the
air cleaner snorkel during engine-off condition, has given SHED
evaporative test results of less than 2 g/test on many production
Vegas and on several modified vehicles. The use of sealed air
cleaners or internal vent valves would be expected to reduce these
emissions to even lower levels. There is no reason why this type
system cannot be adopted to all carbureted engines.
h.	An area of concern in regards to low evaporative emission levels
is the effect on exhaust emission levels. In the Exxon contract
study, the vehicles having lowest exhaust emissions were not adversely
affected by the ECS modifications. However, at exhaust levels
necessary to meet the statutory standards (.41 g/mile HC .and 3.4
g/mile CO) there could be a significant interaction effect between
evaporative and exhaust emissions. The size of any such effect
would depend on the particular type of evaporative-exhaust control
system combination.

-------
-12-
The evaporative systems that might be expected to have the
greatest effect on exhaust emissions are those which store a large
portion of the vapors in the engine induction system. During
engine cranking and/or start-up these vapors are drawn into the
engine and can have a large effect on the air-fuel ratio. This
type of interaction can be minimized (and perhaps essentially
eliminated) by not using the induction system for vapor storage.
Vapors stored in a canister can be purged into the engine during
periods of relatively high air flow rates when the effect on over-
all air-fuel ratio should be negligible. This type of purging is
used most effectively by the current production Vegas.
For catalyst equipped vehicles, the level of HC and CO exhaust
emissions are very low under warmed-up conditions. For this reason
it may be desirable to time delay canister purging until the
catalyst bed is up to operating temperature. Another possible
purging technique for catalyst equipped vehicles would be to inject
the canister stored vapors into the exhaust system during warmed-up
operation. Such an exhaust purge system should essentially elimin-
ate evaporative-exhaust interactions.
4. Conclusions
The above discussion strongly indicates that existing technology
can be applied to meet an evaporative standard of 2.0 g/test by the
proposed SHED procedure. Based on recent variability tests, a
vehicle which has a true SHED evaporative level of 1.90 g/test has
a 90% probability of passing a 2.0 g/test standard. The data cited
in this issue paper cover a wide range of vehicle types. The
results show that some current production vehicles are below a 1.9
g/test level. Other vehicles have met a 1.9 g/test level after
receiving some modifications to the production evaporative control
system.

-------
APPENDIX

-------
APPENDIX \
TABLE I
Summary of evaporative emissions from modified vehicles
Make:	Ford "LTD"
Year: 75
No. : 1
Displ. cu. in./Litre: 351/5.75
Evap. Emissions,
Modifications		g/SHED Test		Remarks
I.a. Purge from inside air cleaner element.
b.	Barrier in air cleaner at base of snorkel.	6.1
c.	Chcke shaft passage sealed.
II. Steps a, b, c
d.	Air horn to body gasket modified to allow more bowl	9.6
vapors to be stored in air cleaner.
IlI.e. Purge to air cleaner snorkel as well as air cleaner.
Measurements were made of purge rates for both an air cleaner and a snorkel purge system. Next, a curve
of grans Temoved from canister vs. total purge volume was made. From these data it was estimated that a3
combination air cleaner-snorkel purge system would remove 13 to 15 grams from the canister during the SHED
preconditioning period (4-LA-4s). This is not an adequate system because the combined diurnal and hot soak
input to the canister is about 23 grams for the modified vehicle. Consequently, a PCV purge system was Installed
using a 1974 Vega canister which had been in daily usage up to this time.
IV. PCV purge with Vega canister. The bottom of the	1.3
canister is capped. An unmodified carburetor body	1.2
to air horn gasket used along with modifications
b and c above.

-------
Attachment 2
Table II
Summary of Evaporative Emissions from Modified Vehicles
Make: Pontiac
Year: 75
No. : 2
Displ. cu. in./Litre: 400/6.56
Modifications
Evap. Emissions,
g/SHED Test
Remarks
I.a. Vented carb. bowl to canister.
b.	Sealed leak around accel.
pump shaft.
II. Steps a and b
c.	Restriction in line from
bowl to canister.
10.5 (diurnal)
3.4
Canister dried up
before run.
III. Steps a, b, c
d.	Underhood ventilated with
a fan.
e.	Bottom on canister.
1.6
2.5
1.7
Fan lowers carb.
temp, about 30°F
NOTE: Upon completion of these tests, a Vega canister was installed,
and tests were conducted without use of the underhood ventilating
fan. Two repeat tests were performed and results were 1.52 and
1.75 g/test.

-------
APPENDIX V
TABLE IV
SUMMARY OF EVAPORATIVE EMISSIONS FROM MODIFIED VEHICLES
Make: Chrysler
Year 75
No.: 21
Displ. cu. in./Litres 440/7.21
Modificationo
I Original ECS
Original ECS
Evap. Emissions,
g/SHED Test
13.4
14,6
Remarks
Diurnal - 6.3 g, H.S. - 7.1 g
Diurnal - 4.4 g, H.S. - 10.2 g
II Modified ECSJ	1
t"
(a)	Two canisters in parallel used	i
(b)	Second carbl bowl vented directly to canister	^
(c)	Bottom on each canister	2*0
(d)	Barrier at base of snorlcel
(e)	Accel, pump shaft leak sealed
o
n*
3
(I)
P

-------
APPENDIX V
TA3LE V
SUMMARY OF EVAPORATIVE EMISSIONS FROM MODIFIED VEHICLES
Make:	Hornet
Year: 74
No.: 11
Displ.	cu. in./Litre: 232/3.80
Eva p. Emis 9 ions,
Modifications	r/SHED Test
I.a. Carb. bowl vented to the canister.	3.9
b.	Accel, pump shaft leak sealed.
II. Steps a and b above - restriction in line from carb.	3.1
bowl to canister.
c.	Barrier installed In air cleaner at base of snorkel.
III. Steps a, b, c above
d.	Bottom of canister closed.	2.5
IV. ECS modified to a PCV purge system using a 1974 Vega ^	1.2
canister. Steps a, b, c, and d above also continued. r	1.3

-------
APPENDIX V
TABLE VI
SUMMARY OF EVAPORATIVE EMISSIONS FROM MODIFIED VEHICLES
Make: Mazda
Year: 74
No.; 15
Displ. Cu In./Litre: 80/1.31 (Rotary)
Evap. Emissions
Step	Modifications		g/SHED Test		Remarks
I	Both carburetor bowls vented to	4.8, 3.8	Hydrocarbon vapors escaping from
a 3 tube canister (Chrysler).	snorkel.
Purge is through existing purge
line to PCV. Original ECS used
for diurnal.
II	Next, the modifications indicated below were tested. In each case, the hydrocarbon level from the
SHED test exceeded 2.0 grams.
1.	Canister moved outside of engine compartment to a cooler environment.	•
2.	Canister dried up on vacuum pump prior to diurnal and hot soak.	g
3.	Air cleaner canister closed off and 3 Lube canister used for both diurnal and not soak.**	t
At this point, additional' source determination tests indicated hydrocarbon vapors emanating from
carburetor throat due to fuel drippage. To alleviate pressure in the carburetor bowl, a fan
installed to lower bowl temperature by ventilating the underhood engine compartment.
Ill	Modifications for Step I0	2.8
Underhood fan to ventilate
underhood.
At this point, the 3 tube canister was changed to a 4 tube Vega with a purge control valve. (Used
canister from 1974 Vega.) High diurnal losses in above runs due to tank vapors passing into engine
crankcase, then through PCV purge line into 3 tube canister. Vapors then moved out of the canister <-t
into the carburetor bowl and air cleaner through the vent line from the bowl to the canister. The	J
purge control valve prcvancs this migration of vapors into the carburetor bowl and air cleaner.	g.
3
IV	Modifications for Step I with	1.8, 1.3	3
exception of replacing 3 tube	^
canister with a 4 tube unit.
Fan to ventilate underhoou.

-------
APPENDIX V
TABLE VII
SUMMARY 0? EVAPORATIVE EMISSIONS FROM MODIFIED VEHICLES
Make:	Volvo
Years 74
No.: 17
Displ. cu. in./Litre; 121/1.98
Modifications
I.a. Equalizing valve modified so as to relieve fuel tank
pressure at 0.5 psig.
Evap. Emissions,
g/SHED Test
0.4
Remarks
CO and HC exhaust levels
higher with modified ECS,
b. Baffle installed between fuel tank and muffler.
c. American Motors canister used.	1,7	^
0?
o
%
(i)
3
ON

-------
Actachment 7
MVMA'SIIED CROSS-CHECK RESULTS
3 97G Chevrolet Vega #76008
Test Laboratory
SITED Emissions (Grams)
Diurnal
Hot Soak
Total
American Motors
Mean
S.D.
.98
1.06
.84
.86
1.03
.95
.10
1.18
1.12
1.06
.93
1.19
1.10
.11
2.16
2.18
1.90
1.79
2.22
2.05
.19 (9%)
Chrysler Corporation
Mean
S.D.
.78
.76
.71
.75
.04
1.12
1.10
1.05
1.09
.04
1.90
1.86
1.76
1.84
.07 (4%)
EPA
Mean
S.D.
.77
.86
.78
.80
.05
1.19
1.16
1.28
1.21
.06
1.96
2.02
2.06
2.01
.06 (3%)
Ford Motor Company
Mean
S.D.
1.21
.92
1.15
1.09
1.09
.12
1.24
1.05
1.19
.85
1.08
.17
2.45
1.97
2.34
1.94
2.17
.26 (12%)
General Motors
Mean
S.D.
.89
.82
1.19
1.25
1.05
.91
.69
.97
.20
.92
1.18
1.04
.84
.99
.89
.90
.97
.12
1.81
2.00
2.23
2.09
2.04
1.80
1.59
1.94
.22 (11%)

-------
Attachment 8
EPA-Ford Correlation Program with Durability Vehicle
7A1-400-5A1NP and 1977 FTP
Test Lab

Exhaust
Emissions
(g/mi)

EPA

HC
CO
NOx



.376
5.55
1.86



.390
5.21
1.86



.356
6.15
1.75



.386
5.97
1.68



.379
4.97
1.68


Mean
.377
5.57
1.77


S.D.
.013
.50
.090


S.D., %
4%
9%
5%

Ford

.464
5.94
1.54



.419
5.38
1.60



.449
6.20
1.63



.556
7.64
1.76



.420
5.23
1.79


Mean
.462
6.08
1.66


S.D.
.056
.96
.107


S.D., %
12%
16%
6%

EPA-420-S-76-100

-------