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) 3-6 82E-5 – 98E-5 SERIES Engine mode Compression pressure at 250 rpm MPa {kg/cm2} Deviation among cylinders MPa {kg/cm2} 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}