With BMW Tester

Fig. 10 Spark Advance Control Wiring Diagram:

To test the vacuum advance control system, use BMW tester# 12 1 460 (advance control simulator) or equivalent and BMW service test unit or BMW digital tester. Perform the test as follows:

1. Disconnect and remove the vacuum advance control unit (located forward of left front shock tower).
2. Connect control unit and connector plug to simulator. Set simulator switch to position "A".
3. Connect BMW service test unit or BMW digital tester.
4. Start engine.
5. Perform engine test step "06" or check ignition timing.
6. The ignition timing value displayed now will be "retarded" approx. 20° on crankshaft by the simulator.
7. Lamp "MV" on the simulator comes on - the solenoid is activated.
8. The vacuum advance solenoid valve (VASV) should let the vacuum flow through the VASV and exit at the ventilation outlet (not at the connection to the intake manifold vacuum hose). The VASV is located above the vacuum brake booster.
9. Lamp "tp" (load signal) will flash throughout the entire test.
10. Perform test steps "A" through "D" according to procedures printed on the simulator.
11. The resistance values for the coolant and intake temperature sensors can be taken at the jacks.
"TW" = coolant temperature
"TA" = intake air temperature
12. Check coolant temperature switch (located in front of engine, top of thermostat housing). If coolant temperature switch is checked below 45°C (113°F), pull off connector at idle control unit (located in glove box above L-jetronic control unit).
13. Disconnect white wire connector at temperature switch and connect an ohmmeter between switch terminal (where white wire would connect) and ground.
14. Ohmmeter should read as follows:
coolant temperature above 45°C (113°F) closed circuit (low or no resistance)
coolant temperature below 30°C (86°F) open circuit (infinite resistance)
15. If measured value is different, replace and retest with new switch. Disconnect ohmmeter and reconnect connector at switch and idle speed control unit.
16. Check intake air temperature sensor (located below air cleaner in left front corner of engine compartment).
17. Disconnect air temperature sensor connector. Measure the resistance between the terminals. Ohm reading should be:
at 10 - 38°C (50 - 100°F) 950 ± 20 ohms
18. If measured value is different, replace and retest with new sensor. Reconnect air temperature sensor connector.
19. For troubleshooting vacuum advance control system, use this chart (simulator connected and engine running at idle):

a. Lamp "tp" not flashing:
No "tp" signal.
No power supply for simulator.
L-jetronic control unit, connections or wire harness defective.
Engine not running correctly or at all.

b. Lamp "MV" not on:
No power supply to simulator.
Wire harness to simulator defective.
Vacuum advance control relay defective.

c. No advance control:
Vacuum advance control relay defective.
Connections or wire harness for solenoid defective.

d. Ignition timing not reached when vacuum is supplied to advance control box:
Solenoid defective.
Vacuum hose leak.
Distributor defective.

20. Repair defective part and recheck system.
21. Disconnect all test equipment and reinstall vacuum advance control unit.