Compression pressure too low
Uniformly low compression pressure is not necessarily a sign of alarm; This may also be due to the measurement tolerances of the various control devices. However, one should think if differences of more than 2-3 bar are measured between individual cylinder indicators. This could mean:
Wear of pistons and piston rings.
Piston ring coking due to deposit formation.
Ellipsism in the cylinders as a result of piston jamming.
Deposits on valve stems or seats due to combustion residues or oil.
Burnt valves. In most cases, loose valves cause insufficient compression pressure and thus reduced engine power.
To manually turn the crankshaft of a 4-cylinder engine, you need to put a 22 mm wrench on the alternator pulley nut. If the belt slips, you must press it.
Troubleshooting
To more accurately determine the malfunction at low compression, the following trick should be applied: drip a little oil from the oil can into the spark plug hole and measure the pressure again.
If the readings are still low, it's the valves.
If you get higher readings, then the piston rings are the cause, or possibly the cylinders as well. The added oil created for a short time a better seal between the pistons and the cylinder walls, so that the compressed gas could hardly escape from there.
System leak test
More accurate results can be obtained by testing the system for leaks, which can be done by some workshops. To do this, compressed air is directed into the combustion chamber through the holes of the spark plugs.
If the combustion chamber being tested loses pressure, this can be seen on the scale of the control device. A relatively large leak can be recognized by listening:
- Trumpet sounds near the exhaust pipe indicate a leaky exhaust valve.
- If air comes out of the air filter housing, the intake valve is faulty.
- In the event of a defective cylinder block gasket or cracked cylinder head, compressed air escapes from an adjacent spark plug hole or from an open coolant expansion tank.
- Worn cylinder walls, cylinder walls, or piston rings allow air into the crankcase, from where it exits through open oil fill pipes or through the dipstick guide tube.
Turning the crankshaft of the engine
For some work, it is necessary either to bring the crankshaft to a certain position, or to turn it.
To do this, in a car with a manual transmission on a flat surface, you need to engage fifth gear and roll the car a little forward or backward. Or:
On a 4-cylinder engine, place a 22mm bent ring wrench on the alternator pulley center nut and turn the engine through the V-belt. If the belt slips, it must be pushed between the pulleys with your free hand and thereby tensioned.
Unscrew the V-belt guard on the 5-cylinder engine.
Compression ratio pressure measurement. Shown here is a compression ratio pressure gauge (compressometer) with measuring card is available in the workshop. For home use, simpler control devices with a pointer are suitable, in addition, they are cheaper.
In this sequence, the nuts of the cylinder head cover of the 5-cylinder engine must be tightened first with 5 Nm, then 10 Nm and lastly 12 Nm.
Place a 32mm open end wrench on the servo pump adapter and rotate the motor through the V-belt.
On a 6-cylinder engine, place a 24mm 12-point replacement socket on the crankshaft pulley center bolt and turn the crankshaft with a ratchet or lever.
Never rotate the engine using the toothed belt gear bolt on the camshaft with the toothed belt guard removed! The toothed belt may jump, resulting in engine damage.
Setting cylinder 1 to top dead center (TDC) ignition timing
In a four-stroke engine, the piston comes to top dead center twice (TDC): the first time when the injected combustible mixture is ignited and the second time after the exhaust gases are ejected, with the re-absorption of the fuel / air mixture starting at the end. Usually, during various adjustment work, the TDC of the ignition moment of the first cylinder is necessary.
4-cylinder and 5-cylinder engines: remove the cover separating the breaker from the ignition distributor, the ignition distributor slider and the protective cover. Put the distributor slider back on and crank the engine until the contact of the slider is above the small mark on the edge of the distributor. Thus, TDC was found.
In order for this to pass as accurately as possible, it will probably be necessary to turn the crankshaft a little to one side or the other until a marking appears in the inspection hole of the gearbox «ABOUT» on the flywheel at the edge of the inspection hole.
6-cylinder engine: remove the toothed belt guard on the right and left (described later in this chapter).
Rotate the crankshaft until both holes in the fixing plates on both camshaft drive gears are inwardly facing each other.
Turn the crankshaft slightly to one side or the other until the marking appears in the inspection hole of the gearbox cover «ABOUT» on the flywheel at the edge of the inspection hole.
On a 5-cylinder engine, it is possible to crank the crankshaft at a special adapter in front of the power steering pump. To do this, place an open end wrench on the hex adapter as shown in the figure. Remove the V-belt cover first (one bolt).
The crankshaft of a 6-cylinder engine is turned with the central bolt of the crankshaft pulley. The tool used is a 12-sided interchangeable socket head 24 mm with a ratchet or lever.
The protective cover of the 6-cylinder engine pictured here did not appear immediately on production engines. The arrows show four quick-release fasteners that must be rotated 90°to the left to remove the protective cover.
TDC is found if the mark «ABOUT» appeared on the flywheel under the edge of the gearbox housing (arrow).
Removing the cylinder head cover
The latest 6-cylinder engines are equipped with a protective cover, which, along with a good appearance, performs the function of noise absorption.
Withdrawal:
Turn the four quick locks 90°to the left with a large screwdriver.
Remove protective cover.
Removing the engine protective cover
4-cylinder engine: Remove crankcase breather hose. Disconnect the wiring harness if necessary.
Loosen the drive cable «gas» and pull it out of the support.
Loosen the fixing nuts.
Remove stiffeners.
Raise the lid.
If necessary, remove the oil deflector.
5-cylinder engine: Remove the brake booster hose from the intake manifold.
Remove upper intake manifold and injection nozzles (chapter «Injection system KE-III-Jetronic and KE-Motronic»).
Remove the idle speed control valve.
Unscrew the fixing nuts, remove the stiffeners.
Remove cover.
6-cylinder engine: Remove engine protection.
Loosen the locking screws.
Raise the lid.
If necessary, remove the oil deflector.
When installing, if possible, install a new gasket.
4 and 5-cylinder engines: do not forget about the stiffening plate under the mounting nuts.
6-cylinder engine: lightly grease the cylinder head cover gasket on the inside and outside with silicone anti-friction agent D 007 000 04.
Apply on all four edges between the cylinder head seal and the camshaft bearing cap a little «Silimate» AMV 174 004 01 from Audi spare parts. Take care not to block the oil hole at the bottom of the camshaft bearing cap.
All engine types: Tighten the nuts or bolts crosswise to 10 Nm, starting from the middle of the cover. On a 5-cylinder engine, additionally pay attention to the sequence and tightening torques (illustration top left).
Another TDC mark for 6-cylinder engines is located on the pulley or the lower protective cover of the toothed belt (arrows).
At TDC of the ignition moment of the first cylinder, the large holes of the setting plates on both camshaft drive gears are directed towards the middle of the engine (arrow). The camshaft gear flange must be horizontal (so that an imaginary horizontal line is formed).
To check the hydraulic tappets, press with a plastic or wooden wedge (1) on an unloaded hydraulic pusher (2). Metal tools that can easily scratch the surface of the hydraulic tappet should not be used.
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