Certain abnormal conditions which sometimes interfere
4. Start the engine and hold an injector follower down
with satisfactory engine operation, together with
with a screw driver to prevent operation of the injector.
methods of determining the cause of such conditions,
If the cylinder has been misfiring, there will be no
are covered on the following pages.
noticeable difference in the hound and operation of the
engine. If the cylinder has been firing properly, there
Satisfactory engine operation depends primarily on:
will be a noticeable difference in the sound and
operation when the injector follower is held down. This
An adequate supply of air compressed to a
is similar to short-circuiting a spark plug in a gasoline
sufficiently high compression pressure.
The injector of the proper amount of fuel at the
5. If the cylinder is firing properly, repeat the procedure
on the other cylinders until the faulty one has been
Lack of power, uneven running, excessive vibration,
stalling at idle speed and hard starting may be caused
6. Provided that the injector operating mechanism of
by either low compression, faulty fuel injection in one or
the faulty cylinder is functioning satisfactorily, remove
more cylinders, or lack of sufficient air.
the fuel injector and install a new one by performing the
removal and installation procedure outlined in Fuel
Since proper compression, fuel injection and the proper
amount of air are important to good engine
performance, detailed procedures for their investigation
7. If installation of a new injector does not eliminate
are given as follows:
Locating a Misfiring Cylinder
Checking Compression Pressure
Start the engine and run it at part load until it
Compression pressure is affected by altitude as shown
reaches normal operating temperature.
in Table 1.
Stop the engine and remove the valve rocker
Check the compression pressure as follows:
cover(s). Discard the gasket(s).
1. Start the engine and run it at approximately one-half
Check the valve clearance. The clearance
rated load until normal operating temperature is
should be .009" (two valve cylinder head) or .024" (four
valve cylinder head).
2. Stop the engine and remove the fuel pipes from the
No. I injector and the fuel connectors.
3. Remove the injector and install adaptor J 7915-02
and pressure gage and hose assembly J 6992 (Fig. I).
4. Use a spare fuel pipe and fabricate a jumper
connection between the fuel inlet and return fuel
Above Sea Level
Fig. 1 Checking Compression Pressure