DETROIT DIESEL
SECTION 8
TROUBLE S H O O T I N G
Certain abnormal conditions which sometimes inter-
4. Start the engine and hold an injector follower down
fere with satisfactory engine operation, together with
with a screw driver to prevent operation of the
methods of determining the cause of such conditions,
injector. If the cylinder has been misfiring, there will
are covered on the following pages,
be no noticeable difference in the sound and operation
of the engine. If the cylinder has been firing properly,
Satisfactory engine operation depends primarily on:
there will be a noticeable difference in the sound and
operation when the injector follower is held down.
This is similar to short-circuiting a spark plug in a
1. An adequate supply of air compressed to a
gasoline engine.
sufficiently high compression pressure.
2. The injector of the proper amount of fuel at the
5. If the cylinder is firing properly, repeat the
right time.
procedure on the other cylinders until the faulty one
has been located.
Lack of power, uneven running, excessive vibration,
stalling at idle speed and hard starting may be caused
6. If the cylinder is misfiring, check the following:
by either low compression, faulty fuel injection in one
or more cylinders, or lack of sufficient air.
a. Check the injector timing (refer to Engine Tune-
Up Procedure).
Since proper compression, fuel injection and the
proper amount of air are important to good engine
b. Check the compression pressure.
performance, detailed procedures for their investiga-
tion are given as follows:
c. Install a new injector.
d. If the cylinder still misfires, remove the cam
follower and check for a worn cam roller,
locating a Misfiring Cylinder
camshaft lobe, bent push rod or worn rocker arm
1. Start the engine and run it at part load until it
bushings.
reaches normal operating temperature.
7. If installation of a new injector does not eliminate
2. Stop the engine and remove the valve rocker
misfiring, check the compression pressure.
cover(s). Discard the gasket(s).
3. Check the valve clearance. The clearance should be
Checking Compression Pressure
.009" (two valve cylinder head) or .024" (four valve
cylinder head).
Compression pressure is affected by altitude as shown
in Table 1.
Check the compression pressure as follows:
1. Start the engine and run it at approximately one-
half rated load until normal operating temperature is
reached.
Minimum Compression
Altitude, Feet
Pressure, psi
Above Sea Level
Std. Engine
"N" Engine
430
0
540
400
2,500
500
370
5,000
465
340
7,500
430
315
395
10,000
Fig. 1 - Checking Compression Pressure
TABLE 1
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