2. Fully warm up the engine to normal operating temperature. The battery must be fully charged. You will need an assistant.
3. On early models with a 1.4L engine, disconnect the low voltage electrical connector on the coil (-Oh) ignition (see chapter 5B). On late models with a 1.4L engine and all models with a 1.6L engine, remove the ignition coil pack from the top of the spark plugs (see chapter 5B). On all models, remove the spark plugs as described in Chapter 1 A.
4. Install a compression gauge in the #1 cylinder spark plug hole. A compression gauge that is screwed into the threaded hole for the candle is preferable.
5. Have an assistant fully depress the accelerator pedal (throttle valve fully open) and turn the engine over with the starter. After one or two revolutions, the compression pressure should rise to a maximum value and then stabilize. Record the highest reading.
6. Repeat the test on the remaining cylinders, recording the pressure readings.
7. The values in all cylinders should be very close; a difference greater than 2 bar between any pair of cylinders indicates a malfunction. Know that on a healthy engine, compression should build up quickly; low compression on the first stroke followed by a gradual increase in pressure on the remaining strokes is a sign of worn piston rings. A low reading on the first stroke that does not increase on the remaining strokes indicates valve leaks or a burnt cylinder head gasket (Cracks in the head could also be the cause). Low compression can also be due to deposits on the back of the valve heads.
8. Although the manufacturer does not list exact compression pressures, any cylinder pressure below 10 bar can be considered abnormal. If in doubt as to the suitability of a particular compression pressure, consult your Peugeot/Citroen dealer or others.
9. If the pressure in any cylinder is very low, perform the following test to find the cause. Pour a full teaspoon of pure oil into this cylinder (through the spark plug hole) and repeat the compression test.
10. If the addition of oil temporarily increases compression, this indicates pressure loss due to cylinder or piston wear. The lack of improvement suggests that leaks or burnt valves or a burnt cylinder head gasket may be the culprit.
11. Low compression in two adjacent cylinders is almost certainly the result of a burnt-out or breakdown of the cylinder head gasket between them. This can confirm the presence of coolant in the engine oil.
12. If the pressure in one cylinder is about 20 percent lower than the others and the engine is slightly rough at idle, the camshaft lobe may be the cause.
13. If the compression is abnormally high, there is likely to be carbon deposits in the combustion chambers. In this case remove a head of cylinders and remove a deposit.
14. Upon completion of the check, install the spark plugs in place (see chapter 1A), connect the ignition coil and/or connect the electrical connectors (see chapter 5B).