GMC 1982 Light Duty Truck, Service Manual

Page: 949 / 1435

ENGINE EMISSION CONTROLS 6E-5
EGR DIAGNOSIS
CONDITION POSSIBLE CAUSE CORRECTION
E n g in e idles a b n o rm a lly rough
a n d /o r stalls.
EGR valve vacu u m hoses
m isro uted.
Leaking EGR valve.
EGR valve gasket failed or loose
EGR attaching bolts.
EGR-TVS.
Im p ro p e r vacu u m to EGR valve
at idle.
Check EGR v alve v ac u u m hose
routing . C orrect as requ ired.
Check EGR v alve fo r correct
o p eratio n .
Check EGR attach ing bolts fo r
tigh tn ess. T ig h ten as requ ired .
If not loose, rem o v e EGR v alve
and inspect gasket. R eplace as
requ ired.
P erform EG R -TV S fu n ctio n al check.
Check vac u u m fro m c arb u reto r
EGR po rt w ith en g in e at stab ilized
o p eratin g te m p e ra tu re and at
curb idle speed. (See checking EGR
valve.)
E n g in e runs rough on light
th ro ttle acceleratio n and has
p o o r p a rt load p e rfo rm an c e .
EGR valve v ac u u m hose
m isro u ted .
Check for loose valve.
Failed EG R-TVS
(TVS open b e lo w 130°F.)
Sticky or binding EGR valve.
W ro n g or no EGR gasket(s)
a n d /o r Spacer.
Check EGR v alve vacu um hose
routing . C o rrect as requ ired.
T o rq u e valve.
S a m e as listing in "E n g in e Idles
A b n o rm a lly R ough a n d /o r
S talls ” c o n d itio n.
Clean EGR passage deposits.
P erform EGR S ystem check.
Install n e w gasket(s), install spacer
(if used), to rq u e attaching parts.
E n g in e stalls on d eceleration s. Tran sd u cer control valve blocked
or air flo w restricted.
Restriction in EGR vacu u m line or
v acu u m signal tube.
Sticking or binding EGR valve.
Check tran sd u cer control v alve
o p eratio n (See Checking Back
Pressure EGR V alve).
Check EGR vacu u m lines fo r kinks,
bends, etc. R e m o ve or replace
hoses as req u ired . (See Checking
EGR V alve).
Check EGR v alve for excessive
deposits causing sticky or b in d in g
o p eratio n .
Perform EGR S ystem Check.
P art th ro ttle en g in e d eto n a tio n .
(N O T IC E : N o n -F u n c tio n in g EGR
v a lv e co u ld c o n trib u te to part
th ro ttle d e to n a tio n . D e to n a tio n
can also be caused by several
o th e r e n g in e varia b le s . P erfo rm
ig n itio n and c a rb u re to r related
d iag n o sis.)
Tran sd u cer control valve blocked
or air flo w restricted.
In sufficient exhau st gas
recirculation flo w during part
th ro ttle accelerations.
C ontrol valve blocked or flo w
restricted.
Check in ternal control v alve
o p eratio n (See Checking EGR
V alve).
Check EGR valve hose rou tin g .
Check EGR v alve o p e ratio n . R ep air
or replace as req u ired. Check EGR-
TV S as listed in "E n g in e Idles
A b n o rm a lly R ough a n d /o r
S talls" section. Replace v a lv e as
req u ired . Check EGR passages and
v alve for excessive deposit.
Clean as requ ired.
Check EGR per service p roced u re.
E n g in e starts but im m e d ia te ly
stalls w h e n cold.
(N O T IC E : S talls a fte r start can
also be caused by carb u reto r
p ro b le m s .)
EGR valve hoses m isrouted.
EG R -TVS system m alfu n ction in g
w h e n en g in e is cold.
Check EGR valve hose routing s.
P erform EG R -TVS fu n ctio n al check.
Fig. 6E-6--EGR Diagnosis