DETROIT DIESEL 53
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 injection 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 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).
3. Check the valve clearance.
4. Start the engine. Then hold an injector follower down with a screw driver to prevent operation of the
Fig. 1 - Checking Compression Pressure
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. Provided the injector operating mechanism of the faulty cylinder is functioning satisfactorily, remove the fuel injector
and install a new one.
7. If installation of a new injector does not eliminate the misfiring, check the compression pressure of the cylinder in
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.
Pressure (psi) at 600 rpm
Above Sea Level
Stop the engine and remove the fuel pipes from the injector and fuel connectors of the No. 1 cylinder.
Remove the injector and install adaptor J 7915-02 and pressure gage and hose assembly J 6992 (Fig. 1).
Use a spare fuel pipe to fabricate a jumper connection between the fuel inlet and return manifold connectors. This
permit fuel from the inlet manifold to flow directly to the return manifold.
Start the engine and run it at a 600 rpm. Observe
November, 1973 SEC. 15.2