Compression check (Nissan Bluebird T12)

The compression test in the engine cylinders is carried out as part of a periodic technical inspection of the engine cylinder-piston group and (sometimes) to determine the cause of a specific malfunction, the presence of which is manifested by a decrease in compression in the cylinders. A decrease in compression may be accompanied by various external manifestations: a decrease in engine power and responsiveness, smoky exhaust, knocking in the cylinder-piston group, etc. The test is carried out on an engine warmed up to normal operating temperature. Disconnect the high-pressure fuel pipes from the injectors, having previously loosened their fastening on the side of the high-pressure fuel pump (loosen the fastening nuts carefully: there is high fuel pressure in the pipes). Disconnect the fuel drain pipe from the injectors. Unscrew all the injectors. Using an adapter, connect the pressure gauge to the hole under the injector of the cylinder being tested.



Disconnect the connector from the fuel shut-off solenoid valve (to prevent fuel from being supplied during the test).



Press the gas pedal all the way down and turn the engine crankshaft with the starter. The crankshaft rotation speed during the test should be about 250 rpm, which requires a normal battery charge during the test. Determine the highest pressure value using the pressure gauge readings. Perform the test as quickly as possible; do not turn the crankshaft with the starter for more than 10 seconds. The compression value in the cylinders is an individual parameter for each engine. The crankshaft rotation speed during the test is not so critical, but it is given for each engine as a test condition under which the specified compression value must be ensured.

If the pressure in the cylinders is lower than required, pour 15-20 cm³ of engine oil into the cylinder through the injector holes and recheck. If the pressure increases during the second measurement, the cause of low compression is in the piston-cylinder coupling (wear of piston, cylinder or piston rings). If the pressure in the cylinder has not changed during the repeated check, the reason for low compression is a loose valve seat. If the pressure in two adjacent cylinders is lower than in the others and does not increase during the repeated check, there is a leak in the cylinder head gasket.