Checking Distributor In

Turning distributor shaft sends an alternating current signal to the CDI control unit. This alternating current signal which increases with engine speed, triggers the control unit to release ignition spark.

Distributor operation can be checked by measuring alternating current.


Never make changes on soft iron teeth of rotor or stator.

Disconnect 2-pole plug connector at wire from distributor to engine harness.

2» Connect a multipurpose tester to the plug and adjust it to measure AC voltage.

If starter is operated with distributor cap taken off, be careful that cap holding springs do not fall into distributor.


This distributor test requires a voltmeter which measures very small AC voltage readings.

3. Operate starter and read voltage . The proper voltage is usually about 0.1 V. An exact reading cannot be made, because voltage depends on starting speed and type of measuring equipment. Distributor is bad and needs to be replaced if there is no voltage or much less than 0.1 V.


Testing Prerequisites

Battery fully charged, fuel in tank, engine or ambient temperature between O and + 4-0 C/32 and 104° F.

(Temperature has a direct influence on measured values).

Note especially information on possible dangers when doing any type of work on CDI system (see Workshop Manual 911, Vol. II, Pages SL 23 and 24).

Starter turns, engine does not start or develops insufficient power

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

12 mm spark present?

Go to Point 8

2. Check distributor cap, distributor rotor, ignition cables and spark plugs. Resistance of ignition cable including plug: 4k ohms.

Resistance of distributor rotor: 5k ohms

Spark from spark plug?

3. Check ignition timing. Timing correct?

Repair secondary circuit

Adjust timing

4. Check fuel system.

Engine receiving sufficient fuel?

Repair fuel system.

5. Check ignition transformer.

Disconnect plug and high voltage wire at ignition transformer.

7. For ignition failure: Disconnect tachometer. If ignition failure is gone, tachometer is defective.

If not, tachometer is good. Ignition failure eliminated?

Engine must start or there must be adequate ignition voltage to engine. If not, there is a mechanical defect.

8. Disconnect plug at air flow sensor contact or bridge terminals 30 and 8 7 on base of relay for fuel pump II.

Check voltage at disconnected control unit plug between terminals 6 and 8 with ignition on. Voltage must equal battery voltage.

Porsche Turbo Ignition Unit

Voltage correct?

Eliminate reason for voltage lossc

9. Check sensor resistance including sensor line at disconnected control unit plug between terminals 3 and 7. Resistance: 490 to 700 ohms.

Resistance correct?

10„ Check ground of sensor coil including sensor line at disconnected control unit plug between terminal 3 and car's ground and terminal 7 and car's ground

Repeat test at two-pole plug in sensor line.

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