Electronic Timing Advance

Electronic Timing Advance (TCI-h with knock control, engine codes HT, RD, PL, RV, PF, 9A)
The timing advance functions are most accurately checked using specialized equipment. An adjustable timing light or an engine analyzer such as Volkswagen special tool no. VW 1367 can be used to accurately read ignition timing throughout the range of advance. Follow the operating instructions provided by the instrument's manufacturer.

Checking Timing Advance (engine codes HT, RD, PL)
On engines with a knock sensor control unit, timing is advanced based on engine rpm and engine load. The signal from the Hall sender serves as the indication of engine rpm. A vacuum hose runs from the intake manifold to the knock sensor control unit so that the control unit can sense engine load.

To check rpm-based timing advance, start the engine and let it idle for a few minutes to establish a base timing value in the control unit. Check this base reading with the timing light. Disconnect the vacuum hose from the knock sensor control unit. Raise the engine rpm and compare the maximum timing advance with the values given in Table h. Turn OFF the engine and reinstall the vacuum hose to the knock sensor control unit.

On HT engines, if the values are not as specified, remove the harness connector from the knock sensor control unit and check for continuity between terminal 11 and ground. If there is no continuity, repair the wiring and repeat the test.

Timing which does not advance as specified indicates that either the knock sensor control unit or the knock sensor is faulty. See Knock Sensor System Fault Diagnosis for information on using the system's built-in diagnostic capability to help pinpoint the problem.

Table h:

Table h. Maximum RPM-Dependent Ignition Timing Advance (engine codes HT, RD, PL).

Check the vacuum advance function only after determining that the rpm dependent timing advance is correct. Start the engine and increase engine speed to approximately 3400 rpm. Record the amount of timing advance and let the engine return to idle. Remove the vacuum hose from the knock sensor control unit and again raise the engine to 3400 rpm. The timing should advance approximately 6° more than the previous reading. If it does not, check the vacuum hose for kinks or leaks. If the hose is not kinked or broken, then the knock sensor control unit may be faulty.

Checking Digifant II and Digifant I Timing Advance (engine codes RV and PF)
Check timing advance only after determining that the basic ignition timing is adjusted to specification. On cars with on board fault diagnosis, check the fault memory and correct any faults before proceeding.

To check timing advance (Digifant):
1. With the engine idling at normal operating temperature, disconnect the coolant temperature sensor connector.
2. Raise the engine speed to a steady 2300 rpm and record the basic ignition timing value.
3. Reconnect the coolant temperature sensor connector.
4. On Digifant II cars, briefly raise the engine speed to at least 3000 rpm, then recheck the timing at 2300 rpm. It should be 30 ± 3° more advanced than it was with the coolant temperature sensor disconnected, the basic timing value plus 30 ± 3°.
5. On Digifant I cars, recheck the timing at 4500 rpm. It should be at least 30° more advanced than it was with the coolant temperature sensor disconnected, the basic timing value plus at least 30°.

On Digifant II, if the timing only advances by about 20°, first check the knock sensor tightening torque as described in Checking and Replacing Knock Sensor, then check knock sensor resistance and check for faults in the wiring harness as described in Troubleshooting Knock Sensor System. If mounting torque, sensor resistance and the wiring harness are all OK, then the Digifant control unit is probably faulty.

On Digifant I, if the timing does not advance as specified, then there is a fault in either the air flow sensor or the control unit.

NOTE: Disconnecting the Digifant I coolant temperature sensor with the engine running will register a fault in the control unit memory, which must then be cleared.

If having the coolant temperature sensor disconnected or connected makes no difference, check the continuity of the coolant temperature sensor wire as described in Troubleshooting Knock Sensor System. If there are no breaks in the wire, then either the Digifant control unit or the temperature sensor is faulty.

Checking Motronic Timing Advance (engine code 9A)
No specifications are given for precisely checking the amount of timing advance on CIS-E Motronic systems. Timing advance is based on engine rpm (the Hall sender), engine load (the air flow sensor potentiometer signal), and engine knocking (the knock sensors and reference sensor). In general, the operation of the timing advance function can be checked using a timing light to check that the timing mark moves when engine idle is increased.

If the timing does not advance at all, first check the knock sensor resistance and mounting bolt torque as described in Checking and Replacing Knock Sensor, then the reference sensor, air flow sensor potentiometer, and system wiring as described in Troubleshooting Knock Sensor System. If torque and resistance are within specification and there are no faulty components or breaks in the wiring, then the Motronic control unit is probably faulty.