TM 5-3895-346-14
TROUBLESHOOTING
ENGINE OVERHAUL
TROUBLESHOOTING
ENGINE OPERATION
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 (refer to Exhaust Valve Clearance Adjustment).
4.
Start the engine. Then hold an injector follower down with a screwdriver 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 Fuel Injector Timing).
b.
Check the compression pressure.
c.
Install a new injector.
d.
If the cylinder still misfires, remove the cam follower (refer to Valve Operating Mechanism)
and check for a worn cam roller, camshaft lobe, bent push rod or worn rocker arm bushing.
Checking Compression Pressure
Compression pressure is affected by altitude as shown in Table 1.
Check the compression pressure as follows:
TABLE 1
Minimum Compression
Altitude Above
Pressure at 600 rpm
Sea Level
Std. Engine "N" Engine
psi
kPa
psi
kPa
Feet
Meters
430
2 963
540
3 721
500
152
400
2 756
500
3 445
2,500
762
370
2 549
465
3 204
5,000
1 524
340
2 343
430
2 963
7,500
2 286
315
2 170
395
2 722
10,000
3 048
441
