Notes on avoiding damage to ignition system - AH15.10-P-0002-01F

ENGINE 104, 119, 120 with LH sequential multiport fuel injection system 

• To avoid damage to control unit, only connect and disconnect the two connectors on control unit when ignition is switched off.
• Terminal 1 of ignition coils must not be short-circuited to GND, e.g. as antitheft protection.
• Only install original ignition system components.
• Do not operate ignition system at starting speed unless all of the ignition cables are connected.
• No tests such as holding ignition cable 4 at a distance to GND, unplugging a spark plug connector or pulling cable 4 out of the ignition coils, may be performed at starting speed or when the engine is running.
• Every high voltage circuit must be loaded with at least 2 kΩ (spark-plug connector).
• If it is necessary to test the ignition spark when providing roadside assistance, this must only be done with a spark plug at a cylinder ignition cable. Ensure that spark plug has good contact to ground.
• Before working at cranking speed, e.g. checking compression pressure, switch off ignition and detach crankshaft position sensor coupling(s) from DI switching unit.

Engine 120 has two fuel injection and ignition systems.

• The DI switching unit is mounted for better heat dissipation with thermal-conduction paste onto the wheel arch panel. When being replaced, the protective foil must not be removed, it does not impair the heat dissipation.

Use of testers and testing units 

• Only connect and disconnect secondary measuring sensor to corresponding ignition cables when vertical engine and ignition are switched off.
• If the short-circuit protection is operated (cylinder comparison) and the engine stays upright, it is not possible to conduct the test with this test instrument.
• Do not connect test lamp to ignition coil terminals 1 and 15.