DETROIT DIESEL
Trouble Shooting
CRANKCASE PRESSURE
EXHAUST BACK PRESSURE
(max. in inches of water)
(max. in inches of Mercury)
Speed (rpm)
No-Load Speed (rpm)
Engine
Engine
2000
2200
1800
2500*
2800*
1800
2000
2200
2500*
2800*
3-53
.5
.5
1.0
.5
.9
1.7
2.1
1.3
3-53
2.7
2.7†
4-53
1.0
.5
.9
.5
.5
2.1
3-53
1.3
4-53
2.7
2.7†
1.0
--
--
--
--
4-53T
--
--
--
--
4-53T
1.8
6v-53
--
--
.9
--
1.0
--
--
6V-53
--
2.7
2.7†
*Engines with four valve cylinder head(s).
*Engine! with four valve cylinder head(s).
†3.8 far Marine engines.
TABLE 3
TABLE 4
fuel will indicate air being drawn into the fuel system
on the suction side of the pump.
If air is present, tighten all fuel line connections
AIR BOX PRESSURE
between the fuel tank and the fuel pump.
(min. in inches of Mercury)
If the fuel flow fails to meet the amount specified, the
Max. Exhaust Rack Pressure (Full Load)
fuel strainer, filter or pump should be serviced.
Speed (rpm)
Engine
1800
2000
2200
2500*
2800*
Crankcase Pressure
6.9
9.3
8.0
3-53
5.5
8.6
6.9
8.0
4-53
5.5
8.6
9.3
The crankcase pressure. indicates the amount of air
33.5
--
4-53T
--
--
--
passing between the oil control rings and the cylinder
--
--
--
6v-53
9.3
8.0
liner into the crankcase, most of which is clean air
from the air box. A slight pressure in the crankcase is
(Zero Exhaust Rack pressure)
desirable to prevent the entrance of dust. A loss of
4.8
6.1
3.8
4.9
6.2
3-53
engine lubricating oil through the breather tube,
6.1
4.8
3.8
4.9
6.2
4-53
crankcase ventilator or dipstick hole in the cylinder
31.5
--
--
--
--
4-53†
block is indicative of excessive crankcase pressure.
4.8
6.1
--
--
--
6V-53
*Engines with four valve cylinder head(s).
The causes of high crankcase pressure may be traced
to excessive blow-by due to worn piston rings, a hole
or crack in a piston crown, loose piston pin retainers,
worn blower oil seals, defective blower, cylinder head
TABLE 5
or end plate gaskets, or excessive exhaust back
pressure. Also, the breather tube or crankcase
scavenging, which results in poor combustion and
ventilator should be checked for obstructions.
higher temperatures.
The crankcase pressure may be checked with a
Causes of high exhaust back pressure are usually a
manometer connected to the oil level dipstick opening
result of an inadequate or improper type of muffler,
in the cylinder block. Check the readings obtained at
an exhaust pipe which is too long or too small in
various engine speeds with the specifications in
diameter, an excessive number of sharp bends in the
Table 3.
exhaust system, or obstructions such as excessive
carbon formation or foreign matter in the exhaust
system.
Exhaust Back Pressure
The exhaust back pressure, measured in inches of
A slight pressure in the exhaust system is normal.
mercury, may be checked with a manometer, or
However, excessive exhaust back pressure seriously
pressure gage, connected to the exhaust manifold.
affects engine operation. It may cause an increase in
Remove the 1/8" pipe plug, which is provided for that
the air box pressure with a resultant loss in the
purpose, from the manifold. If there is no opening
efficiency of the blower. This means less air for
provided, one can be made by drilling an 11/32" hole
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