Component Tests and General Diagnostics
WM 101801 Checking for loss of pressure
Tools
Technical values
Tools and materials
Tool kit for checking for loss of pressure
Recommendation:Leitenberger pressure loss tester
Or: Bosch pressure loss tester EFAW 210 A WE 1066
Information
- The engine must be at operating temperature for carrying out the pressure loss test.
Information
- In the case of new engines that have not yet been fully run in (less than 5,000 km), there may be higher pressure losses than after the run-in period as cylinders, pistons and piston rings have not yet attained their final dimensional stability.
- Differences between the individual cylinders of up to two graduation lines = 4 % pressure loss are not significant.
Assessing the problem
A pressure loss test can be carried out in order to determine the extent of the problem more precisely following a compression pressure test. The leak is located by listening for sounds of escaping air.
The following areas can be checked:
Intake manifolds (checking intake valves)
Exhaust manifolds and exhaust pipes (checking outlet valves)
Positive crankcase ventilation and oil filler neck (checking piston rings)
Coolant filler neck and spark plug bore of adjacent cylinder (checking cylinder head gasket)
Preliminary work
Information
Specifications for wrench sizes (a/f specifications) for screw heads are described as follows:
- Torx screws: (E.) for external Torx, (T.) for internal Torx.
- Hexagon-head bolts (internal and external hexagon): Wrench size (a/f)
1. Start the engine and let it heat up.
DANGER
Vehicle can fall down
- Risk of squashing or crushing
- Risk of damage to the vehicle
-> Do not place any solid objects under the raised vehicle.
-> Ensure that the lifting platform is prevented from lowering.
-> Remove solid objects before lowering the vehicle.
-> Raise the vehicle only at the take-up points provided.
-> The outer take-up points should be used primarily.
2. Raise the vehicle.
-> 4X00IN01 Lifting the vehicle Service and Repair.
3. Remove rear wall cover.
-> 555919 Removing and installing rear wall cover - section on "Removing" Service and Repair.
4. Remove rear wheels.
Socket-wrench insert P300 should be used to avoid damaging the rims.
-> 44051900 Removing and installing wheel Removal and Replacement.
CAUTION
Hot components
- Risk of burns
-> Wear personal protective gear.
5. Remove upper part of heat shield.
-> 261219 Removing and installing heat shield.
5.1. Unscrew two external Torx screws (E10, M6 x 12) and remove heat shield.
6. Remove bar ignition module.
-> 282019 Removing and installing ignition coils Service and Repair.
7. Remove spark plugs.
-> 287020 Removing and installing spark plugs - section on "Removing" Service and Repair.
Using spark plug tool
8. Remove rear and centre underbody panelling.
-> 519319 Removing and installing cover for centre underbody 519319 Removing and installing Cover For Centre Underbody.
-> 519419 Removing and installing cover for rear underbody 519419 Removing and Installing Cover for Rear Underbody.
DANGER
Risk of engine falling down.
- Danger of fatal injury, material damage.
-> Support the engine with the prescribed tool.
9. Support the engine using transmission jack V.A.G. 1383 A WE 1082 and transmission jack plate on the oil pan.
It must only be supported over a large area on the oil pan, not just in one specific area.
10. Remove lower part of engine carrier.
-> 103219 Removing and installing engine carrier - section on "Removing".
Checking for loss of pressure
WARNING
Engine can turn without control (the crankshaft can turn because of the pressure in the cylinder).
- Danger of crushing (injury)
- Tools can become jammed (material damage)
-> The piston must be exactly at top dead centre (TDC) position (secure the crankshaft).
-> Do not touch any belt drive components when building up pressure.
-> Do not insert any tools on the crankshaft belt pulley.
1. Set the piston position (ignition TDC) and connect test tools.
Checking piston position: shown on the 997 II
1.1. Connect the dead-centre position gauge -2-. To do this, screw the adapter -3- into the spark plug thread by hand and tighten hand-tight.
1.2. Turn the crankshaft clockwise at the vibration damper -8- as far as the TDC marking of cylinder 1 using turning device 9773 -7-.
1.3. Determine the piston position (ignition TDC) of the cylinder to be checked using the dead-centre position gauge.
1.3.1. Piston position of the cylinder to be checked is correct:
Continue with Step 1.4 (Fix vibration damper in place).
1.3.2. Piston position of the cylinder to be checked is incorrect:
Continue to turn the crankshaft 360° clockwise at the vibration damper using turning device 9773 -7-.
1.4. Fix vibration damper in place.
Fix the crankshaft in place above the staking bore on the vibration damper using a locating pin 9595/1 -9-.
1.5. Remove the dead-centre position gauge.
TDC position marking
Information
- Pressure of between 6 and 12 bar is required for carrying out the pressure loss test.
- Start the test at cylinder 1 and continue according to firing order (1 - 6 - 2 - 4 - 3 - 5).
2. Set the pressure loss tester.
2.1. Connect the test hose -5- to the pressure loss tester -1-.
2.2. Connect the pressure loss tester to the compressed air.
2.3. Pull and open the pressure-regulating valve -4- until the pointer on the pressure loss tester shows 23 %.
2.4. Lock the pressure-regulating valve by pressing it.
Setting pressure loss tester
3. Connect the pressure loss tester.
3.1. Check that the adapter -3- is seated securely in the spark plug thread.
3.2. Connect the adapter to the test hose -5-.
3.3. Connect the pressure hose -6- to the pressure loss tester -1-.
Connecting pressure loss tester
4. Check the pressure loss.
4.1. The pointer on the pressure gauge must move within the green area (0-25 %).
If there is a loss in pressure of more than 25 %, the pressure loss is no longer acceptable and the source of the problem must be found.
4.2. Pressure loss within tolerance range:
4.2.1. Check the pressure loss on the next cylinder in the same way as for cylinder 1.
Firing order: 1 - 6 - 2 - 4 - 3 - 5
4.3. Pressure loss not within tolerance range:
4.3.1. Locate the leak by listening for sounds of escaping air.
The following areas can be checked:
Intake manifolds (checking intake valves)
Exhaust manifolds and exhaust pipes (checking outlet valves)
Positive crankcase ventilation and oil filler neck (checking piston rings)
Coolant filler neck and spark plug bore of adjacent cylinder (checking cylinder head gasket)
4.3.2. Then, continue checking the next cylinder in the same way as for cylinder 1.
Firing order: 1 - 6 - 2 - 4 - 3 - 5
Subsequent work
DANGER
Risk of engine falling down.
- Danger of fatal injury, material damage.
-> Support the engine with the prescribed tool.
1. Install lower part of engine carrier.
-> 103219 Removing and installing engine carrier - section on "Installing".
2. Transmission jack V.A.G 1383 A WE 1082 can now be removed from the work area.
3. Install underbody panels at the rear and centre.
-> 519319 Removing and installing cover for centre underbody 519319 Removing and installing Cover For Centre Underbody.
-> 519419 Removing and installing cover for rear underbody 519419 Removing and Installing Cover for Rear Underbody.
4. Fit spark plugs.
-> 287020 Removing and installing spark plugs - section on "Installing" Service and Repair.
Using spark plug tool
5. Install bar ignition modules.
-> 282020 Removing and installing ignition coils - section on "Installing" Service and Repair.
=> Tightening torque: 10 Nm (7.5 ftlb.)
6. Install upper part of heat shield.
-> 261219 Removing and installing heat shield - section on "Installing".
6.1. Fit and tighten two external Torx screws (E10, M6 x 12).
=> Tightening torque: 10 Nm (7.5 ftlb.)
7. Mount rear wheels.
Socket-wrench insert P300 should be used to avoid damaging the rims.
-> 44051900 Removing and installing wheel Removal and Replacement.
8. Install rear wall cover.
-> 555919 Removing and installing rear wall cover - section on "Installing" Service and Repair.