Compression test in cylinders Mitsubishi Outlander XL 2007 - 2012

Tools (for 4B12/4B11 engines):

• Open end wrench 10 mm
• Ratchet wrench
• Extension
• Head 10 mm
• Candle wrench (or 16mm tall socket)
• Compressometer
• Syringe (if needed)
• Compressor (if needed)

Tools (for 6B31 engine):

• Open-end wrench 8 mm
• Open end wrench 10 mm
• Ratchet wrench
• Extension
• Head 10 mm
• Head 12 mm
• Screwdriver flat medium
• Phillips screwdriver, medium
• Curved round nose pliers
• Pliers
• Knife (or scraper)
• torque wrench
• Candle wrench (or 16mm tall socket)
• Compressometer
• Syringe (if needed)
• Compressor (if needed)

Parts and consumables:

• 1540A193 upper intake manifold gasket (for 6B31 engine)
• Engine oil (if necessary)
• Hose (if needed)
• Cleaner (or solvent, for 6V31 engine, if necessary)
• rags

Notes:

Diagnostics of Mitsubishi Outlander HL engines without disassembly is carried out using compression measurement. By its average value and by the difference in values ​​in individual cylinders, it is possible to determine with sufficient accuracy the degree of general wear of the parts of the cylinder-piston group of the engine, as well as to find out the malfunctions of this group and parts of the valve mechanism.
Measurement of compression in the engine is carried out by a special device - a compression gauge. They come in slightly different designs. With a threaded fitting that is screwed into the spark plug socket. And compression gauges with a rubber tip, which just need to be pressed firmly into the spark plug hole.

Important conditions for the correctness of the readings when checking compression are the serviceability of the starter and its electrical circuits, as well as the full charge of the battery.

1.  Start the engine and warm it up to operating temperature.

2.1. (engine 4B11/4B12)  Open the hood and unscrew the head 10 mm three bolts securing the cylinder head cover plate.

2.2. (Engine 6V31) Remove the decorative casing of the engine  and the intake manifold .

3. Reduce the pressure in the engine power system as described in this article.

4. Disconnect the wire blocks from the ignition coils.

5. Using a 10 mm head, unscrew the ignition coil mounting bolts (the first two photos are the 4B12 engine; the third photo is the 6B31 engine).

6. Remove the ignition coils from the spark plug wells by pulling them up.

Note:

Be extremely careful when handling coils. Even the slightest blow to them can lead to their failure.

7. Turn out a spark plug and take it from a candle well.

8.  Screw the compression gauge into the spark plug hole of the cylinder to be checked.

9.  Press the accelerator pedal all the way so that when the crankshaft is turned by the starter, the throttle valve is fully opened in the engine cylinder purge mode.

10.  Turn on the starter and turn the engine crankshaft with it until the pressure in the cylinder stops increasing. This corresponds to about four compression strokes.

Note:

To obtain the correct readings of the compression gauge, the crankshaft must rotate at a frequency of 180-200 / min. or higher, but not more than 350/min.

11.  Write down the readings of the compression gauge and set its needle to zero by pressing the air release valve.

Note:

For compression meters of a different design, readings can be reset in other ways (in accordance with the instructions for the device).

12.  Repeat steps 8-11 for other cylinders. The pressure should not be lower than 1.0 MPa and should not differ in different cylinders by more than 0.1 MPa.

Note:

Low compression in one cylinder can result from a loose valve seat, damaged cylinder head gasket, broken or burnt piston rings. Low compression in all cylinders indicates worn piston rings.

13.  To find out the reasons for insufficient compression, pour about 20 ml of clean engine oil into the cylinder with reduced compression with a syringe with a hose and measure the compression again.

Note:

If the readings of the compression gauge have increased, the most likely malfunction of the piston rings. If the compression remains unchanged, it means that the valve plates do not fit snugly against their seats or the cylinder head gasket is damaged.
The cause of insufficient compression can also be found out by supplying compressed air to the cylinder in which the piston is previously set to TDC of the compression stroke. To do this, remove the tip from the compression gauge and attach the compressor hose to it. Insert the tip into the spark plug hole and inject air into the cylinder at a pressure of 0.2-0.3 MPa. To prevent the engine crankshaft from turning, engage a higher gear and brake the vehicle with the parking brake. The exit (leakage) of air through the throttle assembly indicates a leak in the intake valve, and through the muffler, a leak in the exhaust valve. If the cylinder head gasket is damaged, air will escape through the neck of the expansion tank in the form of bubbles.

14.  After checking the compression, install all removed parts in reverse order.

The article is missing:

• Tool photo

Source:  carpedia.club