High Voltage Tests

Fig. 1 Air Gap Symbol:

Check high voltage side of ignition system
a. Check the resistance across the rotor contacts. Resistance should be 1000 Ohms ± 20%. If the resistance is incorrect, or if there are any signs of wear, burning, or cracking, replace the rotor.
b. Check spark plug wires.
1. If the spark plug connectors have sheet metal jackets, identified by this symbol Fig. 1, they contain "air gap" resistors and cannot be checked with an ohmmeter. An oscilloscope must be used to test these.
2. If the spark plug connectors do not have air gap resistors, resistance should be:
Angled caps at coil and distributor -- 1000 Ohms ± 20%
Shielded spark plug connectors -- 5000 Ohms ± 20%
c. Check rotor, cap, plugs and plug wires for hairline cracks or carbon tracking.
d. Check spark plugs for proper heat range, electrode gap, and general condition.
Note; BMW uses solid core wire with screw on resistors at each end. Because of this, all wires should have about the same resistance, regardless of length (compared to carbon core wire in which the resistance increases with the length of the wire).