Compression check (Mitsubishi Lancer 9)

1. Before checking, check the level and condition of the engine oil, the condition of the starter and the battery.

2. Before starting the inspection procedure, prepare the vehicle (see section "Checking the idle speed").

3. (MPI engines) Disconnect the spark plug wires.

4. Remove the ignition coils and remove all spark plugs.

5. Disconnect the crankshaft position sensor connector.

Note: This operation is necessary to prevent the engine control unit from sending commands for fuel injection and ignition.

6. Cover the spark plug holes with a clean rag and, after turning the crankshaft with the starter, check that there are no foreign particles on the rag.

Attention:

• Stay clear of the spark plug holes while cranking the engine with the starter.
• If coolant, oil, fuel, etc. gets into the cylinder during compression measurement (as a result of cracks), these substances will heat up and fly out of the spark plug hole under pressure, which is a dangerous phenomenon.

7. Install the compression gauge into the spark plug hole.







8. Turn the engine crankshaft with the starter at fully open throttle and measure the compression.

Compression:

Engine 4G15-GDI:

• nominal - 1755 kPa
• minimum permissible - 1275 kPa
• rotation speed when cranking with starter - 250 rpm

Engine 4G93-GDI:

• nominal - 1720 kPa
• minimum allowable - 1334 kPa
• rotation speed when cranking with starter - 300 rpm

Engine 4G15-MPI:

• nominal - 1608 kPa
• minimum permissible - 1275 kPa
• rotation speed when cranking with starter - 300 rpm

Engine 4G93-MPI:

• nominal - 1226 kPa
• minimum allowable - 1030 kPa
• rotation speed when cranking with starter - 300 rpm

Note: Compression values shown are valid only at the specified crankshaft speed.

9. Measure the compression in all cylinders and check that the difference in compression between the cylinders is less than the maximum permissible value. The maximum permissible value is no more than 98 kPa

10. If the compression in any cylinder is below the minimum permissible value or the difference in compression between cylinders exceeds the maximum permissible value, then pour some engine oil into the spark plug hole of that cylinder and repeat the measurements according to points "8" and "9".

Attention:

• 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.
• 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.

11. Connect the wire harness connector to the crankshaft position sensor.



12. Install the spark plugs and ignition coils.

13. (MPI engines) Connect the spark plug wires to the spark plugs and ignition coils.

14. Clear the fault codes that appeared as a result of disconnecting the crankshaft position sensor connector from the engine control unit memory (see the corresponding section in the chapter "Fuel injection system").