101802 Performing pressure loss test on DFI engines

WM 101802 Performing pressure loss test on DFI engines

Preliminary work

1. Unscrew all spark plugs. -> 287020 Removing and installing spark plugs on DFI engines Service and Repair
2. Position cylinder to be tested to ignition TDC and remove tool (dead centre finder).
2.1. The dead centre finder or "cylinder pipe" consists of a glass tube (inspection glass) with a piston -1- , hose and a rubber cone -2-.





Dead centre finder or "cylinder pipe"

2.2. The rubber cone is pressed onto the spark plug hole. The inspection glass is either held by a helper => Tool setup for dead centre finder or is secured vertically in a clearly visible position with a magnet.





Tool setup for dead centre finder

2.3. If the engine is now turned in direction of rotation on the crankshaft, the piston in the inspection glass is pressed up in the compression cycle => Piston up in order to go back down immediately upon reaching the TDC. The piston in the inspection glass stays down in overlapping TDC => Piston down.





Piston up





Piston down

Tools and materials

Tools

Information

- The tool described here is an example of a pressure loss tester available from various manufacturers.

- The procedure is essentially the same for all pressure loss testers.





Tool kit for testing pressure loss






Information

Test evaluation

- The test does not show any meaningful result on a new engine (i.e. one that hasn't been run in).
- A difference in pressure loss between the individual cylinders of approx. 5% is not significant.
- If the test shows an excessive loss of pressure (> 30%), a few drops of oil can be sprayed into the combustion chamber. Repeat the test. If the loss in pressure is now significantly less, the seal between the piston and cylinder is damaged.
- The air that is escaping causes hissing noises, which provide information about the component that is causing the damage.

If the limit values are exceeded, the engine must be started and the test repeated.






Testing pressure loss from the engine

Checking pressure loss

WARNING

Rotating components

- Danger of limbs being trapped or severed

-> Do not reach into the danger area.

Information

Read the work steps and tips in the operating instructions for the Bosch tester before performing the pressure loss test. The described Bosch tester is used as an example for all suitable pressure loss testers. Details of calibration and use can be found in the relevant operating instructions.

Information

The piston must be exactly at the upper return point when checking pressure loss. Do not touch any components of the belt drive and do not put any tools on the crankshaft pulley while performing the check.

Information

- The check for loss of pressure can be used to assess the mechanical condition of a combustion engine.

- The percentage leakage quantity can be used to establish whether the leaks in the combustion chamber in question are so large that the combustion chamber must be repaired.

- The worn components (e.g. piston rings) can be identified by the compressed air that is escaping.

1. Position cylinder to be tested to ignition TDC and remove tool. The ignition TDC of cylinder 1 (and the remaining cylinders) can be tested using the "dead centre finder" contained in WE1066 pressure loss tester Bosch EFAW 210 A.





TDC for cylinder 1

2. Screw the test hose into the spark plug thread of cylinder 1 by hand (compression TDC) and tighten hand-tight.





Test hose

3. Connect the pressure loss tester to the compressed air system.
4. Adjust the scale. To do this, insert the test nozzle at the front into the device.





Test nozzle

5. Turn the adjusting wheel until the scale pointer is at the "cal." marking or "23%".





Adjusting the scale

6. Remove the test nozzle and check that the pointer falls back. Connect the test hose. The value that is displayed should not be greater than 25 %. If the loss in pressure is greater, it is safe to assume that the engine needs an overhaul.





Pressure loss test

7. Interrupt the compressed air supply and unscrew the test hose.
8. Check the next cylinder by turning the crankshaft through another 120° and check the next cylinder in the firing order.

V6 firing order: 1 - 5 - 3 - 6 - 2 - 4
9. Remove the test hose once the test is complete.

Subsequent work

1. Remove the test hose once the test is complete and install the spark plugs. -> 287020 Removing and installing spark plugs on DFI engines Service and Repair