Checking the spark plugs (VW Passat B4)

Disconnect the terminal or wire of the starting plug and connect an ohmmeter to the terminal of the plug and to the threaded part of the plug body, or connect a test lamp to the positive terminal of the plug, as shown in Fig. 3-57. If the lamp does not light or the ohmmeter shows "infinity", this means the spark plug circuit is broken and must be replaced. Connect an ammeter to the circuit. The total current for four spark plugs should be 48 A, i.e. 12 Ax4. If the ammeter shows 36 A, this means one spark plug is faulty, etc. In this case, the battery voltage was at least 11.5 V. Remove the injectors and check the appearance of the starting plugs in each combustion chamber with the preheating system turned on. A few seconds after turning on the preheating system, the starting plug should glow red. If the spark plug does not glow or the color of the spark plug differs from the others, check its connection, serviceability and resistance.

Burning of the starting plug may be caused by a faulty injector. If burning of the head "1" (Fig. 3-58) of the spark plug or spiral "2" is detected, replace the starting plug and check the fuel spray cone and the tightness of the injector of the same cylinder.