Checking the compression in the cylinders (Nissan Murano Z50)

Checking the compression in the cylinders will show the condition of the upper part of the engine (i.e. pistons, rings, valves, head gasket). Specifically, this test will tell you if low compression is caused by a leak due to worn piston rings, faulty valves and seats, or a bad head gasket.

Caution: The engine must be at normal operating temperature and the battery must be fully charged when performing this check.

Start by cleaning the areas around the spark plugs before you remove them. If you have a source of compressed air, you should use it for this purpose, but a soft brush or even a regular bicycle pump will also work. The point of this is to prevent dirt from getting into the cylinders when performing a compression test.

• Relieve the fuel pressure in the fuel system and do not install the fuel pump fuse during the inspection.
• Remove the engine cover.
• Remove the ignition coils and spark plugs from all cylinders.
• Lock the throttle valve in the fully open position.
• Insert the tip of the compression tester into the hole of the first spark plug.

Compression tester for gasoline engines

Caution: The diameter of the compression tester tip must be less than 20 mm, otherwise the compression tester will get stuck in the cylinder head.

• Crank the engine shaft with the starter for at least seven compression strokes, monitoring the compression gauge readings.

• The pressure should build up quickly in a healthy engine. Low pressure during the first stroke, accompanied by a gradual increase in pressure during subsequent strokes, indicates worn piston rings. Low pressure during the first strokes, which does not increase during subsequent strokes, may be due to leaking valves or a damaged cylinder head gasket (the cause could also be a crack in the head). Low pressure can also be caused by deposits on the valve heads. Record the obtained pressure values.
• Repeat this operation for the remaining cylinders and compare the measurement results with the technical data.

Engine speed, not less than, rpm	Compression pressure, kgf/cm²
	minimum	norm
300	10	13

• The difference in pressure values between the cylinders should be no more than 1.0 kgf/cm².
• Find the maximum compression value you obtained in the table - on the right will be the minimum allowable compression value, and then compare it with the minimum value you obtained.

Maximum kg*s/cm²	Minimum kgf/cm²
1	2
2	1
9,23	6,96
9,37	7,03
9,51	7,17
9,65	7,23
9,79	7,37
9,92	7,44
10,06	7,58
10,20	7,65
10,34	7,79
10,48	7,86
10,61	7,92
10,75	8,06
10,89	8,13
11,03	8,27
11,16	8,34
11,30	8,48
11,44	8,58
11,58	8,68
11,72	8,75
11,85	8,89
11,99	9,03
12,06	9,10
12,27	9,17
12,41	9,30
12,54	9,37
12,68	9,51
12,82	9,65
12,96	9,72
13,10	9,79
13,23	9,92
13,37	9,99
13,51	10,13
13,65	10,20
13,79	10,34
13,92	10,41
14,66	10,54
14,20	10,61
14,34	10,75
14,47	10,82
14,61	10,89
14,75	11,03
14,89	11,16
15,03	11,23
15,60	11,37
15,30	11,44
15,44	15,58
15,58	11,65
15,72	11,79
15,85	11,85
15,99	11,99
16,13	12,06
16,27	12,20
16,41	12,27
16,54	12,41
16,68	12,48
16,82	12,61
16,96	12,68
17,04	12,82
17,23	12.89

[Data copied from web resource: www.NissanBook.ru]

• If the compression on one or more cylinders is low, add some engine oil (about a tablespoon) into the spark plug hole of each cylinder and repeat the measurements.
• If the compression increases after pouring oil into the cylinders, this means that the piston rings and/or cylinder bore are worn. If the compression has not increased significantly, then the leak is in the valves or in the cylinder head gasket. Valve leakage can be caused by burned valve seats and/or warped, cracked or bent valves.
• If two adjacent cylinders have equally low compression readings, there is a good chance that the head gasket between them is damaged. The presence of coolant in the combustion chambers or crankcase may confirm these suspicions.
• If the compression in one cylinder is about 20% lower than the others, and the engine idles slightly rough and/or backfires, a worn cam lobe on the camshaft could be the cause.
• The difference in compression between the cylinders must not be less than the maximum permissible value.
• Maximum permissible value: no more than 1.00 kgf/cm².
• If the compression is unusually high, the combustion chambers may be coated with carbon deposits. If this is the case, the cylinder head must be removed and the carbon deposits removed.
• If compression is low or varies greatly from one cylinder to another, it is recommended to check for leaks. This test will accurately indicate the presence of a leak and help estimate its size.