3-6 82E-5 – 98E-5 SERIES
3. TROUBLESHOOTING
3.3 Troubleshooting by Measuring Compression Pressure
Compression pressure drop is one of major causes of increasing blowby gas (lubricating oil contamination or
increased lubricating oil consumption as a resultant phenomenon) or starting failure. The compression pres-
sure is affected by the following factors:
1) Degree of clearance between piston and cylinder
2) Degree of clearance at intake/exhaust valve seat
3) Gas leak from nozzle gasket or cylinder head gasket
In other words, the pressure drops due to increased parts wear and reduced durability resulting from long use of
the engine.
A pressure drop may also be caused by scratched cylinder or piston by dust entrance from the dirty air cleaner
element or worn or broken piston ring. Measure the compression pressure to diagnose presence of any abnor-
mality in the engine.
(1) Compression pressure measurement method
1) After warming up the engine, remove the
fuel injection pipe and valves from the
cylinder to be measured.
2) Crank the engine before installing the
compression gauge adapter.
*1 Perform cranking with the stop handle
at the stop position (no injection state).
*2 See 12.2 - 18 in Chapter 12 for the com-
pression gauge and compression gauge
adapter.
3) Install the compression gauge and
compression gauge adapter at the cylinder
to be measured.
*1 Never forget to install a gasket at the tip
end of the adapter.
4) With the engine set to the same state as in
2)-*1, crank the engine by the starter motor
until the compression gauge reading is
stabilized.
(2) Standard compression pressure
Engine compression pressure list (reference value)
Engine mode
Compression pressure at 250 rpm
MPa {kg/cm
2
}
Deviation among cylinders
MPa {kg/cm
2
}
Standard Limit
3D82AE 3.16 ± 0.1 {31 ± 1} 2.45 ± 0.1 {25 ± 1}
0.2 – 0.3 {2 – 3}
3D84E, 4D84E 3.24 ± 0.1 {33 ± 1} 2.55 ± 0.1 {26 ± 1}
S3D84E, S4D84E 2.94 ± 0.1 {30 ± 1} 2.45 ± 0.1 {25 ± 1}
4D88E – (S)4D98E 3.43 ± 0.1 {35 ± 1} 2.75 ± 0.1 {28 ± 1}
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