Mitsubishi 6M70 - On-Vehicle Inspection and Adjustment; Measuring Compression Pressure

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1. Measuring Compression Pressure
Service standards
Special tools (Unit: mm)
• A drop in compression pressure can be used as a guide to determine when the engine should be overhauled.
• Measure the compression pressure at regular intervals. Keeping track of its transitions can provide a useful tool
for troubleshooting. On new vehicles and vehicles with newly replaced parts, the compression pressure will be
somewhat higher depending on the break-in condition of piston rings, valve seats, etc., but this will return to nor-
mal as the parts wear down.
• Before the compression measurement, confirm that the engine oil, starter, and battery are in normal condition.
• Place the vehicle in the following cond
itions.
• Warm up the engine until the coolant temperature reaches approximately 75 to 85°C.
• Turn off the lights and accessories.
• Place the transmission in N range.
• Turn the steering wheel in neutral position.
• Remove the fuse (M25) from the fuse box in the cab to prevent
fuel from being injected while the engine is cranked using the
starter.
CAUTION
• When cranking the engine, never shut off the power sup-
plied to the engine electronic control unit by disconnecting
the engine electronic control unit connector or other similar
methods. If the engine is cranked with the power to the en-
gine electronic control unit shut off, the supply pump will
not be controlled by the electronic control unit, causing the
supply pump to be malfunctioned.
Location Maintenance item Standard value Limit Remedy
–
Mitsubishi 6M70
Compression press
ure
Each cylinder (at 200 rpm)
2,940 kPa
{30 kgf/cm
2
}
1,960 kPa
{20 kgf/cm
2
}
Inspect
Pressure difference be-
tween each cylinder
–
390 kPa
{4 kgf/cm
2
}
or less
Inspect
Mark Tool name and shape Part No. Application
MH062180 Measuring of compression pressure
Compression gauge
adapter
A
M14 × 1.5
ON-VEHICLE INSPECTION AND ADJUSTMENT