Note: An appropriate compression tester must be used to carry out this check.
If engine performance deteriorates, intermittent operation occurs that cannot be attributed to malfunctions of the ignition or fuel system, a compression test will provide an idea of \u200b\u200bthe condition of the engine.
Note: The engine must be at operating temperature and the battery must be fully charged. Exercise caution when working on vehicles equipped with a catalytic converter.
Remove the spark plugs from the engine.
Disconnect the wires from the ignition coil (on models with separate low voltage wires to the coil, disconnect the wire from the terminal "15" on a reel), and on models with fuel injection, remove the fuel pump relay.
Connect a compression tester to the #1 spark plug hole.
Let the assistant press but stop the accelerator pedal. while cranking the crankshaft for about 4 seconds using the starter. After one or two turns, the arrow of the device will show the maximum compression level, then stop. Record these instrument readings.
Repeat tests while recording data.
All cylinders should show almost the same pressure; deviation indicates that there is some kind of problem. Pay attention to that. that in a serviceable engine, pressure builds up quickly. Low pressure on the first piston stroke, followed by a gradual increase in pressure on subsequent strokes, indicates wear on the piston tracks. Low pressure on the instrument during the first piston stroke. which does not increase during the last strokes of the piston, indicates leakage through the valves or a rupture of the gasket between the cylinder head (a cracked cylinder head can also be the cause of this). Carbon deposits on the bottom of the valve head can also be the cause of low pressure.
If the pressure in one of the cylinders is significantly lower than in the others, carry out the following test to determine the cause. Pour a teaspoon of clean engine oil into the appropriate cylinder through the spark plug hole and retest.
If the addition of oil temporarily improved compression. this indicates that the cylinder or piston is worn. If there is no improvement, then this indicates a leak or sooted valves, as well as a suggestion that the cylinder head gasket has cracked.
Low pressure levels in two adjacent cylinders definitely indicate that. that here the fault is a crack in the cylinder head gasket; the presence of coolant in the engine oil confirms this fact.
If one cylinder reads 20% lower. than others, and the engine knocks slightly at idle, the cause may be wear on the camshaft cam.
If the reading is unusually high, then the combustion chambers are probably covered with a layer of soot. It is necessary to remove the cylinder head and remove it.
After completing the test, replace the spark plugs and connect the wires to the ignition coils.
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