Measuring compression pressure (Audi 100 C4)

Drive a little to bring the engine up to operating temperature. Piston rings seal better when the oil is warm.

Turn off the ignition and fuel supply. This is done differently in different models:

4-cylinder engine: Disconnect the plug on the electronic ignition coil switch.

Disconnect the multi-pin plug on the central injection (74 kW engine) or remove fuse #17 in the fuse box (85 kW engine with Digifant injection system) or plugs of all four injection nozzles (85 kW engine).

5-cylinder engine: Disconnect the plug on the electronic ignition coil switch.

Remove fuse #17 in the fuse box.

6-cylinder engine: Disconnect both connectors on the electronic ignition coil switch.

Disconnect the plugs of all six injection nozzles. Additionally, disconnect the holders of the high-voltage wires of the fuel line of the third and fourth cylinders.

All models: Remove all spark plugs.

Press the rubber cone of the pressure measuring device to the spark plug hole of the first cylinder (the order is not important, but it must be written down) or to the connecting cable leading to the spark plug socket thread.

Set the car to the parking brake, set the manual transmission gearshift lever to neutral, and the automatic transmission gearshift lever to the "P" position.

Ask an assistant to turn the engine over with the starter. The accelerator pedal should be fully depressed (for better filling of cylinders).

When the pressure reading stops increasing, write it down and move on to the next cylinder.