Computers and Control Systems: Testing and Inspection

TROUBLESHOOTING ELECTRONIC IGNITION SYSTEM (BOSCH CDI)

NOTE: The Electronic Ignition System (Bosch CDI) system used on this vehicle does not produce or store Diagnostic Trouble Codes (DTC's). Therefore there is no procedure to access them.


Test Requirements:
Battery fully charged, fuel in tank, engine or ambient temperature between 0 and 40° C. (Temperature has a heavy influence on the measured values.)

Pay attention to the information on dangers for any type of work on the CDI system.

Starter turns, engine does not start or develops insufficient power

1. Connect spark gap to ignition transformer (coil) terminal 4 and set it for 12 mm. Start engine.

12 mm spark exists?
no Continue at Point 8
yes Continue to 2

2. Check distributor cap. distributor rotor, ignition lines and spark plugs.




Resistance of ignition line including plug: 4 kohms.




Resistance of distributor rotor: 5 kohms

Spark from spark plug?
no Repair high voltage end
yes Continue to 3

3. Check ignition timing.
Timing correct?
no Adjust timing
yes Continue to 4

4. Check fuel system.
Engine receiving sufficient fuel
no Repair fuel system
yes Continue to 5

5. Check ignition transformer.
Disconnect plug and high voltage wire at ignition transformer.




Ignition transformer primary (term. A and 9): 0.10 to 0.165 ohms
Ignition transformer secondary (term. 4 and A): 390 to 630 ohms

Resistance correct?
no Replace ignition transformer (coil)
yes Continue to 6

6. Check wires and plugs of ignition system (CDI control unit, ignition/starter switch, distributor, ignition transformer, tachometer) for tightness and oxidation.
Everything correct?
no Eliminate defects
yes Continue to 7

7. For ignition failure:
Disconnect tachometer.
If ignition failure is gone. the tachometer has a defect. If not, the tachometer is good.
Ignition failure eliminated?
no Replace control unit
yes Engine must start or there must be engine output. If not, there is a mechanical defect.




8. Disconnect wire plugs at air flow sensor contact or bridge terminals 30 and 87 on base of relay for fuel pump II.




Check voltage at disconnected control unit plug between terminals 6 and 8 with the ignition on. The voltage must equal the battery voltage.
Voltage correct?
no Eliminate break in supply line.
yes Continue to 9




9. Check sensor resistance including sensor line at disconnected control unit plug between terminals 3 and 7.
Resistance: 490 to 700 ohms.
Resistance correct?
no Repeat test at two-pole plug in sensor line.



Test values correct: Repair or replace wires between plug and CDI control unit.
Test values incorrect: Replace distributor.
yes Continue to 10




10. Check ground of sensor coil including sensor line at disconnected control unit plug between terminal 8 and car's ground and terminal 7 and car's ground.
Resistance infinite?
no Repeat test at 2-pole plug in sensor line (see step 9)
yes Continue to 11




11. Check sensor system for mechanical damage. Visual inspection: Is there clearance between the rotor and stator?
Sensor system good?
no Replace distributor
yes Continue to 12

12. Disconnect tachometer.
If there's an ignition spark now, the tachometer is defective.
Tachometer good?
no Replace tachometer
yes Continue at Point 5