Chevrolet DB90 Series, Service Manual

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S ec. 6C -76
53 AND 71 SERIES DIESEL ENGINES
M A N O M E T E R
[ (C o n n e cte d to e x h a u s t to
I test e x h a u s t b a c k p re s su re )
T # «
M A N O M E T E R
(Connected to air inlet to
test air intake restriction)
Figure
20
—A ir Inlet and Exhaust Pressure Check (TypicalI
A reading higher than sp ecifica tio n s indicates
the following:
1. D irty air c lea n ers.
2. Damaged air clea n ers.
EXHAUST BACK PRESSURE
(R efer to Figure 20)
A sligh t p r e ssu r e in the exhaust sy ste m is
norm al. H owever, e x c e s s iv e exhaust b a ck p ressu re
se r io u sly a ffects engine operation. It may cau se an
in c r e a se in the a ir box p r e ssu r e with a resultant
lo s s of efficien cy of the blow er. This m eans le s s
a ir for scavenging which r e su lts in poor com bus­
tion and higher tem p eratu res. The maximum ex ­
haust back p r e ssu r e (no-load) is shown in the fo l­
lowing chart:
NOTE: Due to variation s in exhaust sy ste m s
(horizontal or v ertica l stacks) the above chart is
typical.
EXHAUST BACK PRESSURE - NO LOAD
(Max. in Inches of Mercury)
Engine
6V-53
6-71
V-71
1 2 0 0
1.2
.09
SPEED (RPM)
1800
2.8
2.1
2000
3.5
2. 6
2100
3.5
2.6
2600
~ 2 7
r
The exhaust b a c k p r e s s u r e , m easured in inch­
e s of m ercury, may be checked with the m anom eter
in the Engine D iagn osis T est Kit (J-9531-01 or
J-22506) (fig. 20). The m anom eter or p ressu r e
gauge is connected to the exhaust m anifold by r e ­
moving the 1/8" pipe plug which is provided for
that purpose. If there i s no opening provided, one
can be m ade by drilling an 1 1 /3 2 ” hole in the ex ­
haust m anifold companion flange and tapping a 1/8"
pipe thread.
Check the readings obtained at variou s sp eed s
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL SUPPLEMENT