EPA-AA-TAEB 76-21
Emission Testing of 1974 Pontiac V-8 with
Defective Thermal Vacuum Valves
June 1976
Technology Assessment and Evaluation Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Protection Agency
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Introduction
The EPA recently became aware that there were problems with the
Thermal Vacuum Valve (TW) installed in 1974 Pontiac V-8's. To confirm
the existence of the problem, functional tests were conducted on TW's
collected from in-service Pontiac vehicles. These tests consisted of
applying a controlled vacuum to the valves while raising their temperature
in a stepwise fashion and observing when they actuated. The majority of
the valves tested failed to meet their design specifications. The
functional tests are described in Appendix A.
Next, in order to quantify the effect of the failed valves on
emissions, exhaust emissions tests were conducted with the TW's installed
in a 1974 Pontiac. However due to a heavy test schedule in the Motor
Vehicle Emission Laboratory, only a limited test program was undertaken.
This report describes the exhaust emission test program and presents the
data and results.
The conclusions drawn from these tests are necessarily of limited
applicability. A complete evaluation of the degradation of the emission
control system caused by defective TVVs on the 1974 Pontiac V-8's requires
a much larger sample of test vehicles than is economically feasible in
the in-house test projects conducted by EPA. To fully evaluate the
system degradation, it is necessary that a more extensive test program
be carried out.
The conclusions drawn from this test can be considered to be
quantitatively valid only for the specific vehicle used in the test
program. Although it is reasonable to extrapolate the results from the
test to other 1974 Pontiac engine/powertrains in a directional or
qualitative manner, tests of the TVVs on other such vehicles would be
required to reliably quantify the results on other engine/powertrain
combinations. However, because of the magnitude and consistency of the
directional trend for NOx emissions found in this test, one can
reasonably conclude that a failed TW can cause NOx increases
substantial enough to create a high probability that the vehicle would
fail to meet the applicable NOx standard.
System Description
The 1974 Pontiac V-8 uses an emission control system that employs a
transmission controlled spark (TCS) to control distributor advance and
exhaust gas recirculation (EGR). Engine vacuum signals supplied at the
carburetor are used to control the EGR valve and distributor advance.
The sending of these signals is controlled in part by the TVV.
The valve, Figure 1, is a dual function thermal switch. It is
activated by intake manifold air temperature. The valve allows a vacuum
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Seal
Cricn
Manifold Vacuum
Port on
Carburetor
Distributor
rj Vacuum
EGR Port on
Carburetor
EGR Valve
Upp-?r Housing
Figure 1 1974 Pontiac V-8 Thermal Vacuum Valve (Dole)
Specifications: Harrison
Dole
EGR starts to open 57 + 5F
between normally closed port C to E
Distributor closed 62°F + 5°F
between normally open port M to D
Calibrated EGR on and dis-
tributor off at 62°F + 3°F
EGR on < 57°F
EGR off> 67°F
Distributor on < 57°F
Distributor off > 67°F
Note: Dole and Harrison valves are functionally identical.
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signal to be sent to the EGR valve at temperatures above 62 F. It
simultaneously shuts off the direct vacuum signal to the distributor.
The typical installation schematic is shown in Figure 2.
The test vehicle was a 1974 Pontiac LeMans Sport (the vehicle is
described in detail on the following page). To ensure that the test
results would be representative, the vehicle was thoroughly checked out
and tuned up prior to testing. Major items checked were cylinder compres-
sion, dwell, timing, idle rpm, idle CO, exhaust system, cooling and fuel
systems. Air, oil, and fuel filters were replaced. New sparkplugs,
points, condenser and PCV valve were installed and the oil was changed.
The EGR valve and the carburetor on the vehicle were malfunctioning, and
were replaced with new units. The vehicle was then tuned to manufacturer's
specifications.
Test Procedure
Exhaust emission tests were conducted according to the 1975 Federal
Test Procedure ('75 FTP), described in the Federal Register of November 15,
1972 except that no evaporative emissions tests were conducted. All
testing was conducted using an inertia weight of 4500 pounds (2041 kg)
with a road load setting of 14.0 horsepower (10.4 kw) at 50 miles per
hour (80.5 km/hr).
Two baseline tests were run with the vehicle adjusted to manu-
facturer's specifications. After completion of the baseline tests, mal-
functioning TWs were installed on the test vehicle. Two tests were run
on the test vehicle with each TW. The TWs tested were selected to be
representative of the types of failures noted during the previous bench
checks. The valves tested were:
TVV Number Fault
32 New valve, no malfunctions
6 No EGR, no vacuum advance shutoff
14 Late EGR (170 F), no vacuum advance shutoff
1 No EGR, late vacuum advance shutoff (150°F)
•2 No EGR, late vacuum advance shutoff (150°F)
Test Results
Exhaust emissions data, summarized below, showed that the defective
TWs caused the NOx emissions from the test car to exceed the standard
for the 1974 model year. Results are expressed as '74 FTP emissions,
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TO AIR CLEANER
EGR VALVE
TO MANIFOLD VACUUM
PORT ON CARBURETOR
DISTRIBUTOR SPARK &
E.G.R. THERMAL VACUUM
VALVE
TO EGR PORT ON
CARBURETOR
DISTRIBUTOR VACUUM SPARK
DELAY VALVE
IGNITION SWITCH
DISTRIBUTOR VACUUM
DIAPHRAGM
DISTRIBUTOR VACUUM
ADVANCE SOLENOID
240°
HOT COOLANT
SWITCH
COLD FEED
SWITCH
TCS
SWITCH
IDLE STOP
SOLENOID
Figure 2 Typical Emission Control System for 1974 Pontiac V-8
Typical Specifications:
EGR Valve 2" Hg starts to open
5" Hg fully open
.7 to .8 Ib./min exhaust flow
Distributor Advance 7" Hg 0° Advance
14" Hg 20° Advance
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TEST VEHICLE DESCRIPTION
Chassis model year/make - 1974 Pontiac LeMans
Emission control system - EGR, Transmission Controlled Spark (TCS)
Engine
type 4 stroke, Otto cycle, OHV, V-8
bore x stroke 3.875 x 3.746 in.
displacement 350 cu. in.
compression ratio 7.6:1
maximum power @ rpm
fuel metering . single 2 barrel carburetor
fuel requirement regular unleaded (tested with
indolene HO, unleaded)
Drive Train
transmission type 3 speed automatic
final drive ratio ......... 2.73:1
Chassis
type body-on-frame, front engine, rear drive
tire size HR 78 x 14
curb weight 4140 pounds
inertia weight .... 4500 pounds
passenger capacity 5
Emission Control System
basic type . EGR, transmission controlled spark
advance (TCS)
durability accumulated on system . 27,850 miles
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the procedure used to certify the vehicle. This test is a cold start
LA-4 driving cycle and consists of the first two test phases of the '75
FTP (Bag 1 and Bag 2). Detailed results appear at the end of this
report.
'74 FTP Mass Emissions
grams per mile
(grams per kilometre)
average of two tests
TW No.
HC
CO
C02
NOx
Fuel Economy
(Fuel Consumption)
32
6
14
1
2
74 Federal
Standards
2.16
(1.34)
2.89
(1.80)
3.10
(1.92)
2.50
(1.55)
2.47
(1.54)
3.4
21.84
(13.57)
17.97
(11.17)
18.62
(11.57)
21.34
(13.26)
19.71
(12.25)
39.0
838
(517)
749
(465)
719
(447)
796
(495)
758
(471)
1.51
(.94)
4.45
(2.77)
4.56
(2.83)
4.19
(2.60)
3.99
(2.48)
3.0
10.1 miles/gal.
(23.2 litres/lOOkm)
11.3 miles/gal.
(20.9 litres/lOOkm)
11.7 miles/gal.
(20.2 litres/ 100km)
10.6 miles/gal.
(22.2 litres/lOOkm)
11.1 miles/gal.
(21.1 litres/lOOkm)
Expressed as a percentage change from baseline, the results showed:
'74 FTP Mass Emissions
Percent change from Baseline*
TW no.
6
14
1
2
HC
CO
C02
NOx
Fuel Economy
34%
44%
16%
14%
-18%*
-15%*
- 2%*
-10%*
-11%*
-14%*
- 5%*
-10%*
195%
202%
178%
164%
12%
16%
5%
10%
A negative sign indicates a decrease in emissions/fuel economy.
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Thus, although the defective valves improved CO emissions and fuel
economy, they increased HC and NOx emissions. The increase in NOx emis-
sions was sufficient to cause the vehicle to fail to meet the 1974
emission standards. While there was an improvement in fuel economy,
comparative certification data for the 1975 and 1976 equivalent vehicle
showed fuel economies of 10.8 and 12.9 miles per gallon respectively,
even though these cars met more stringent exhaust emissions standards.
For one test on valves number 2 and 14 a thermocouple was attached
to the valve body. The time/temperature trace showed a gradual rise
from ambient (70 F) conditions to operating temperatures (150 F); at
between 50% and 80% of the '74 FTP driving cycle the temperature would
stabilize at 150 F. Since this is probably representative of the warmup
cycle each valve would experience, a comparison of the valve faults and
emission test results leads to several additional conclusions about the
valves' effects on emissions. The change in HC and CO emissions was
largely the result of late vacuum shutoff. The change in NOx emissions
is largely the result of lack of EGR.
Conclusions
Thermal vacuum valves which failed to meet specifications in the
functional tests caused high NOx emissions (in excess of the 1974
standard) when installed in the test vehicle, a 1974 Pontiac 350.
Installation of the defective valves also caused hydrocarbon
emissions to increase significantly, carbon monoxide emissions to
decrease slightly and fuel economy to improve slightly.
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'75 FTP Mass Emissions
grams per mile
Valve
Number
32
32
6
6
14
14
1
1
2
2
Test Number
77-1683
77-1727
77-1728
77-1800
77-1804
77-2070
77-1801
77-2071
77-1985
77-2070
HC
2.94
2.45
3.06
3.06
3.29
3.35
3.15
3.57
3.15
3.31
— oag a. v
CO
36.72
31.33
29.35
29.01
27.23
31.02
28.22
36.19
29.97
29.18
C02
859
866
758
784
722
722
725
802
722
739
NOx
1.78
1.67
4.95
5.46
5.16
5.73
4.78
6.34
5.15
5.82
Fuel
Eco.
MPG
9.6
9.6
10.9
10..6
11.4
11.4 '
11.4
10.2
11.4
11.2
HC
1.83
1.47
2.78
2.68
3.04
2.74
1.70
1.71
1.85
1.70
— Dag t. i
CO
10.37
11.17
7.34
8.03
9.02.
8.91
12.80
9.90
11.21
10.09
10 L OLc
C02
.788
822
725
732
715
718
794
859
775
793
ju-Lj.j.zet
NOx
1.48
1.16
3.58
3.92
3.49
3.99
2.16
3.69
2.50
2.72
i —
Fuel
Eco.
MPG
11.0
10.5
11.9
11.8
12.0
12.0
10.8
10.1
11.1
10.9
HC
2.25
1.75
: 2.61
2.48
3.07
. 2.64
1.93
.. 1.82
1.97
1.86
oag j
CO
14.61
15.78
8.46
7.90
13.03
10.00
12.27
11.94
13.90
11.36
not i]
C02
663
710
650
660
620
620
622
736
665
685
ransieni
NOx
1.93
1.49
5.70
.6.16
4.26
6.03
3.64
5.78
4.00
4.48
Fuel
Eco.
MPG
12.8
12.0
13.2
13.1
13.6
13.8
12.9
11.7
12.8
12.5.
Valve Number
'75 FTP Composite Mass Emissions
grams per mile
Test Number
HC
CO
C02
NOx
Fuel Eco. MPG
32
32
6
6
14
14
1
1 .
2
2
77-1683
77-1727
77-1728
77-1800
77-1804
77-2070
77-1801
77-2071
77-1985
77-2140
2.18
1.75
2.79
2.71
3.10
2.84
2.06
2.60
2.12
2.08
16.95
16.58
12.17
12.31
13.86
13.76
15.83
15.87
15.81
14.37
769
800
711
723
691
692
744 '
813
734
753
1.67
1.35
4.44
4.85
4.04
4.90
3.10
4.80
3.45
3.84
11.1
10.7
12.0
11.8
12.3
12.3
11.4
10.5
11.6
11.3
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Appendix A
Functional Tests
of Pontiac Thermal Vacuum Valves
Twenty-eight Thermal Vacuum Valves (TW's) removed from in-use
Pontiac V-8 automobiles were tested at the EPA Motor Vehicle Emission
Laboratory to determine whether the valves actuated as they are
designed to do.
The tests consisted of applying a controlled vacuum to the valve
at the proper port, while raising the actuation temperature in a
stepwise fashion and observing when the valve actuated by measuring
the vacuum at another port. For instance, referring to Figure A-l:
vacuum applied to port 'M' was observed with a vacuum gage at port 'D1.
Likewise, a vacuum applied at port 'C1 was observed at port 'E'. The
valves were also checked for leaks.
Vacuum test results are depicted in Figure A-2 in which valve
actuation temperature for each function is shown for each valve. Of
the twenty-eight valves tested (number 10 was broken and not tested),
twenty-five did not provide the required vacuum signal at the design
temperature.- Principal faults were late cutoff of distributor manifold
vacuum, late EGR actuation and early EGR actuation.
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. 10
A-2
Seal
Crliap
Manifold Vacuum
Port oa
Carburetor
Distributor
EGR Port oa
Carburetor
EGR Valve
Upper Housing
Figure A-l 1974 Pontiac V-8 Thermal Vacuum Valve (Dole)
Specifications: Harrison
EGR starts to open 57 + 5°F
between normally closed port C to E
Distributor closed 62°F + 5°F
between normally open port M to D
Dole
Calibrated EGR on and dis-
tributor off at 62°F + 3°F
EGR on < 57°F
EGR off> 67°F
Distributor on < 57°F
Distributor off > 67°F
Note: Dole and. Harrison valves nre functibnallv identical.
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11
A-3
2io°-
190°-
170° -
150°.
130°.
110°-
90°
?n°
/u -
50°-
1 5
Lai
— «^— i
Le
.EG
1
10 '
R
—
"1
15'
Early
20'
1
i
EGR
25
New
Valve
X
' ' ' 30
Valve Number
EGR Valve Actuation
210°-
190°.
170"
150" H
130°
110C
90C
r
Late Distributor Cutoff
L
New Valve,**
Early Distributor Cutoff
/e/H
10
15 20
Valve Number
25
30
Direct Distributor Vacuum Advance
Figure A-2 Summary of Functional Test Results
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