Compression check (Opel Frontera B)

The condition of the engine can be checked by measuring the compression in the cylinders. If this check is carried out regularly, it is possible to know in advance the beginning of engine wear, without waiting for the moment when wear manifests itself in low engine efficiency. Based on the results of the check, it is possible to judge the condition of the valves or pistons (piston rings), and also whether the engine has exhausted its service life and is subject to replacement or major repairs.

To check the compression, you need a compression tester with a rubber cone tip with a measurement range of up to 40 bar.

The engine must be warmed up to a temperature of 90°C and the battery fully charged.

Remove all spark plugs.

Disconnect the wiring harness connector from the ignition control unit, thereby disabling the ignition system.

Remove the fuel pump relay.

Turn on the starter and check that the engine crankshaft rotates at approximately 300 min⁻¹.

Insert the tip of the compression tester into the spark plug hole of the first cylinder.

The assistant must press the accelerator pedal all the way down (i.e. fully open the throttle valve) and turn the engine crankshaft with the starter for 4 seconds. Write down the result obtained.

Note: When checking compression, do not stand in front of the spark plug holes, as when the crankshaft is turned by the starter, engine oil and fuel may be ejected from the cylinders through the spark plug holes.

Check the pressure in the remaining cylinders in the same way.



All cylinders should have approximately the same pressure, greater than 10 bar (145 psi). A pressure difference of more than 1 bar between any two cylinders indicates a fault.

Note that the compression value should increase quickly on a healthy engine; low compression on the first revolution of the crankshaft, followed by a gradual increase on subsequent revolutions of the crankshaft, indicates wear of the piston rings. A low compression value on the first revolution of the crankshaft, which increases slightly later, indicates a loose valve fit, a broken cylinder head gasket, or a crack in the cylinder head. Carbon deposits on the valve backs can also cause low compression.

If the compression in one cylinder is low, then perform the following test. Pour some engine oil into the cylinder through the spark plug hole and check the compression.

If pouring oil into the cylinder increases compression, this indicates that the cylinder or piston rings are worn out. The lack of an increase in compression indicates that there may be a leak through burnt valves or a blown head gasket.

Low pressure in two adjacent cylinders indicates a burnt-out gasket between the cylinders, and engine oil should appear in the coolant.

If the pressure in one of the cylinders is 20% lower than in the other cylinders and the engine runs unsteadily at idle, then the camshaft cam is worn out.

If the compression pressure is too high, this indicates that the combustion chamber is covered with a thick layer of carbon deposits. In this case, it is necessary to remove the cylinder head and remove the carbon deposits.



After checking, screw in the spark plugs, tighten them to a torque of 18 N·m and restore the functioning of the ignition system.

Install the fuel pump relay.