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