Chevrolet 1977 light duty truck, Руководство по обслуживанию

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EGR TVS
PURPLE
STRIPE
Fig. 6E-22--EGR System-V8
5. ^ T o rq u e clam p bolt to 13-18 lb. ft.
6. C onnect c a rb u re to r vacuum signal line to tube
at top o f valve.
T H E R M A L V A C U U M S W IT C H (T V S )
Replacement
1. D isconnect vacuum lines (Figs. 6E-22 and 23)
from the th e rm al vacuum switch.
2. R em ove switch fro m th erm o sta t housing.
3. A pply a n a pproved sealer to th read e d p o rtio n o f
switch.
4. Install switch in th e rm o sta t housing an d torque
to 100 lbs. in.
5. R o tate switch head as re q u ired to align fo r
p ro p e r hose routing.
6. Install vacuum hoses to switch.
Functional Check
H ot
NO TE: This is to be perfo rm ed as p a rt o f the
em ission m ain ten an ce routine at 12,000 m iles or 12
m onths on heavy duty em ission vehicles.
The E G R T h erm al V acuum D elay Switch should be
open above coolant tem p eratu re 100 °F (38 “C ) on L6 and
120°F (49
°C)
on V8 p e rm ittin g the ported vacuum signal
to reach the E G R valve above th a t tem p eratu re. Check
as follows:
1. Rem ove E G R valve vacuum hose at E G R valve
an d connect hose to a vacuum gage.
2. S tart engine. W ith transm ission selector lever in
N e u tra l or P ark o pen throttle p artially. (D o not
overspeed engine.) As throttle is opened, the vacuum
gage should respond w ith an increase in vacuum reading.
(N ote: C oolant te m p eratu re m ust be above 120 °F (49 "C)
d u rin g this test. Allow ab o u t 3 m intues at idle to w arm
up a cold engine. If coolant is below 75 °F (24 ^C)) g reater
tim e m ay be req u ired .)
3. If o p eratio n is satisfactory, rem ove gage and
reconnect hose to E G R valve.
If gage does n o t respond to th ro ttle opening,
proceed to Step 4.
4. Rem ove C arb-to-sw itch hose from switch and
connect hose to vacuum gage. R ep eat Step 2.
5. If vacuum gage responds to throttle opening,
th en switch is defective. Rem ove switch an d replace w ith
new part.
If gage does n o t respond to throttle opening, then
check fo r plugged hose or defective carb u reto r.
Cold
N O TE: This check m ay be p erfo rm e d in diag n o s­
ing com plaint o f stall a fte r cold start o r p o o r
d riv eab ility im m ed iately a fte r cold start.
The E G R th erm al vacuum delay switch should be
closed below coolant tem p eratu re 100 °F (3 8 ' t ) on L6 on
120°F (49 "C) on V8, thereb y blocking the p orted vacuum
signal from reach in g the E G R valve below th at
tem p eratu re. Check as follows:
1. D ra in c o o la n t below level o f th e rm o sta t
housing.
2. D isconnect vacuum lines and rem ove switch
from th erm o stat housing.
3. Inspect switch to m ake sure it is in good
condition.
4. C onnect a vacuum hose to lower nipple o f
switch, m arked
" C "
o r "C A R B :. C onnect a vacuum gage
to u pper nipple, m arked " E " o r " E G R " .
5. Place switch in w ater at 8 5 °F ( 2 9 ^ ) and
subm erge com pletely fo r 2 m intues w hile a g ita tin g w ater
thoroughly.
6. A pply 12 in. hg. (-41 kPa) vacuum to hose on
lower nipple o f switch. U n d e r this condition, the switch
should be closed.
N O TE: L eakage o f up to 2in. hg. (-7kPa) o f