2. Disconnect the high-tension spark plug wires.
3. Remove all spark plugs.
4. Disconnect the crankshaft position sensor connector.
Note: This measure will prevent the Engine Control Unit (ECU) from commanding fuel injection and ignition.
5. Cover the spark plug holes with a clean rag and, after turning the crankshaft with the starter, check for foreign particles on it.
Caution: Stay clear of spark plug holes while cranking the engine with the starter.
Caution: If during the compression measurement in the cylinder (as a result of cracks appearing) coolant, oil, fuel, etc. got into it. and, the above mentioned substances will heat up and be ejected under pressure from the spark plug hole, which can be dangerous.
6. Install the pressure gauge into the spark plug hole.
7. Turn the crankshaft with the starter at fully open throttle and measure the compression.
Model with 6V31 engine:
- Nominal value (at 200 min⁻¹): 1460 kPa.
- Maximum permissible value (at 200 min⁻¹): minimum 1050 kPa.
Model with 6G7 engine:
- Nominal value (at 200 min⁻¹): 1710 kPa
- Maximum permissible value (at 200 min⁻¹): minimum 950 kPa
Model with 4M4 engine:
- Nominal value (at 280 min⁻¹): 2800 kPa
- Maximum permissible value (at 280 min⁻¹): minimum 2500 kPa
8. Measure the compression in all cylinders and check that the difference in compression between the cylinders is less than the maximum permissible value.
Maximum permissible value:
- Model with 6V31 engine: no more than 98 kPa.
- Model with 6G7 engine: no more than 98 kPa
- Model with 4M4 engine: no more than 300 kPa
9. If the compression in any cylinder exceeds the maximum permissible value or the difference in compression between cylinders exceeds the maximum permissible value, then pour a little motor oil into the spark plug hole of that cylinder and repeat the measurements in points 7 and 8.
1) If the compression has increased after adding oil, the cause of the malfunction is wear or damage to the piston ring and/or cylinder bore.
2) If the compression does not increase after adding oil, the reasons are burnt or damaged valve seat, or gas (pressure) leakage through the cylinder head gasket.
10. Connect the crankshaft position sensor connector.
11. Install the spark plugs, tighten them, and connect the high-voltage wires to them.
12. To erase the fault code, use MUT-III.
[The material was borrowed from the website: MitsubishiMan]
Note: This operation will erase the fault code resulting from disconnecting the crankshaft position sensor connector from the ECU memory.