Compression in cylinders — check (Renault Scenic 1)

Compression testing allows you to draw conclusions about the condition of the engine. Only when checking can it be determined whether the valves or pistons are worn out (piston rings) or they are in normal condition. In addition, the test results show whether the engine needs to be replaced or whether it only needs to be completely overhauled. For testing, a compression tester is required, which is offered by specialized stores for gasoline engines at an affordable price.

Attention! For diesel engines, a compression tester with a large measurement range of almost 40 bar is required.

The pressure difference in individual cylinders can be a maximum of 1.5 bar. If the pressure in one or more cylinders differs from the pressure in other cylinders by more than 1.5 bar, this indicates a defect in the valves, wear of the piston knees or working surfaces of the cylinders.

1. Warm up the engine to measure the compression. To do this, drive some distance until the coolant reaches operating temperature. Once the coolant temperature reaches the desired value, drive another 5 km or so to ensure sufficient oil temperature, which should be +80°C.

2. Shift into neutral and apply the parking brake.

3. Gasoline-powered vehicles: Disconnect fuel pump relay B to prevent fuel from being supplied when the engine is started (see illustration).





4. Cars with petrol engines. Disconnect the high-voltage wire tips from the spark plugs using special pliers, such as HAZET 1849-1. Then blow out the spark plug seating areas with compressed air and air and unscrew the spark plugs with the appropriate spark plug wrench.

5. Vehicles with diesel engines: Disconnect the fuel shut-off valve plug to prevent fuel from being supplied and injected by the injectors into the combustion chambers of the cylinders.

6. Vehicles with diesel engines: Remove all glow plugs.

7. Turn the engine over a couple of times with the starter to throw out carbon deposits and soot.

Caution! Do not lean over the engine compartment when turning the engine. Risk of injury from small solid particles ejected from the engine.

8. Press or screw the compression tester into the spark plug/glow plug socket according to the instructions in the operating instructions.

9. Ask the assistant to press the accelerator pedal all the way down and hold it in this position until the check is completed.

10. Let the engine turn over approximately 8 revolutions until the pressure reading on the gauge stops increasing.

11. Check all cylinders one by one and compare the results with the nominal compression value.

Installation

Cars with gasoline engines

12. Connect the fuel pump and ignition system relay.

13. Screw in the spark plugs and fit the high-tension wire caps onto them, see the relevant chapter.

Diesel Engine Cars

14. Connect the fuel shut-off valve plug.

15. Screw in all glow plugs.