Checking the automatic ignition advance (VW Passat B4)

To check the ignition timing depending on the crankshaft speed:

• warm up the engine to operating temperature and stop it;
• connect the control tachometer and stroboscope in accordance with the operating instructions;
• run the engine at idle speed;
• determine the value of the ignition timing angle;
• disconnect the vacuum hose from the electronic ignition timing control unit;
• increase the crankshaft speed to 4600 rpm and determine the ignition timing angle in this mode.

Subtract the value determined at idle from this value. If the resulting difference in values is greater or less than 18°, replace the control unit.

To check the ignition timing depending on the engine load (vacuum in the intake manifold):

• check the ignition timing angle values depending on the crankshaft speed;
• allow the engine to run at a crankshaft speed of 4600 rpm;
• disconnect the vacuum hose from the control unit.

In this case, the ignition advance angle should decrease by approximately 20°. If this does not happen, replace the control unit.