Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSMITSUBISHI2004DIAMANTE V6-3.5L SOHCREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTTUNE-UP AND ENGINE PERFORMANCE CHECKSCOMPRESSION CHECKTESTING AND INSPECTION
2004 Mitsubishi Diamante V6-3.5L SOHC
Compression Check: Testing and Inspection
2004 Mitsubishi Diamante V6-3.5L SOHCSECTION Testing and Inspection
COMPRESSION PRESSURE CHECK
1. Before inspection, check that the engine oil, starter and battery are normal. Also, set the vehicle to the following condition.
- Engine coolant temperature: 80 - 95°C (176 - 203°F)
- Lights and all accessories: OFF
- Transmission: P range
2. Disconnect the spark plug cables.
3. Remove all of the spark plugs.
4. Disconnect the crankshaft position sensor connector.
NOTE: Doing this will prevent the engine control module from carrying out ignition and fuel injection.
5. Cover the spark plug hole with a rag, and after the engine has been cranked, check that no foreign material is adhering to the rag.
WARNING: Keep away from the spark plug hole when cranking.
WARNING: Do not let water, oil, fuel, etc. enter the cylinder through cracks, or these heated materials will gush out from the spark plug hole, which is dangerous.
6. Set the compression gauge to a spark plug mounting hole.
7. Crank the engine with the throttle valve fully open and measure the compression pressure.
Standard value: 1200 kPa (171 psi)/250 - 400 r/min
Limit: minimum 890 kPa (127 psi)/250 - 400 r/min
8. Measure the compression of all the cylinders, and check that the pressure differences of the cylinders are below the limit.
Limit: maximum 100 kPa (14 psi.)
9. If there is a cylinder with compression or a compression difference that is outside the limit, pour a small amount of engine oil through the spark plug hole, and repeat the operations in steps (6) to (8).
1. If the compression increases after oil is added, the cause of the malfunction is a worn or damaged piston ring and/or cylinder inner surface.
2. If the compression does not rise after oil is added, the cause is a burnt or defective valve seat, or pressure leaking from the gasket.
10. Reconnect the crankshaft position sensor connector.
11. Reinstall the spark plugs and spark plug cables.
12. Use the scan tool to erase the diagnostic trouble codes, or disconnect the negative battery cable for 10 seconds or more and then re-connect it.
NOTE: This will erase the diagnostic trouble code resulting from the crankshaft position sensor connector being disconnected.
1. Before inspection, check that the engine oil, starter and battery are normal. Also, set the vehicle to the following condition.
- Engine coolant temperature: 80 - 95°C (176 - 203°F)
- Lights and all accessories: OFF
- Transmission: P range
2. Disconnect the spark plug cables.
3. Remove all of the spark plugs.
4. Disconnect the crankshaft position sensor connector.
NOTE: Doing this will prevent the engine control module from carrying out ignition and fuel injection.
5. Cover the spark plug hole with a rag, and after the engine has been cranked, check that no foreign material is adhering to the rag.
WARNING: Keep away from the spark plug hole when cranking.
WARNING: Do not let water, oil, fuel, etc. enter the cylinder through cracks, or these heated materials will gush out from the spark plug hole, which is dangerous.
6. Set the compression gauge to a spark plug mounting hole.
7. Crank the engine with the throttle valve fully open and measure the compression pressure.
Standard value: 1200 kPa (171 psi)/250 - 400 r/min
Limit: minimum 890 kPa (127 psi)/250 - 400 r/min
8. Measure the compression of all the cylinders, and check that the pressure differences of the cylinders are below the limit.
Limit: maximum 100 kPa (14 psi.)
9. If there is a cylinder with compression or a compression difference that is outside the limit, pour a small amount of engine oil through the spark plug hole, and repeat the operations in steps (6) to (8).
1. If the compression increases after oil is added, the cause of the malfunction is a worn or damaged piston ring and/or cylinder inner surface.
2. If the compression does not rise after oil is added, the cause is a burnt or defective valve seat, or pressure leaking from the gasket.
10. Reconnect the crankshaft position sensor connector.
11. Reinstall the spark plugs and spark plug cables.
12. Use the scan tool to erase the diagnostic trouble codes, or disconnect the negative battery cable for 10 seconds or more and then re-connect it.
NOTE: This will erase the diagnostic trouble code resulting from the crankshaft position sensor connector being disconnected.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.