Home ReviewsRefund
Home/Saab/900/Saab 900 I (1978-1994)/Repair manual/Ignition System/Ignition System - Bosch Hall Effect
Contents Section: Ignition System All sections

Ignition System - Bosch Hall Effect Saab 900 I

Ignition System 1 illustration ~982 words

DESCRIPTION

The typical Bosch Hall Effect electronic ignition system consists of an ignition coil, Hall Effect sending unit (in distributor), Hall control unit, distributor, spark plug wires, and spark plugs.

The Hall Effect sending unit receives voltage directly from the electronic control unit. Signals from the sending unit are sent to the Hall control unit through an electronic ignition control unit.

During engine operation, ignition timing is controlled by the electronic ignition control unit after receiving signals from the knock sensor, idle switch, full throttle switch, and engine vacuum (vacuum hose is connected directly into ignition control unit).

OPERATION

The Hall Effect sending unit is mounted inside the distributor on a switch plate. A trigger wheel attached to the distributor shaft under the rotor, passes in and out of the air gap of the Hall Effect sending unit. There is 1 trigger wheel shutter for each cylinder of the engine. Shutter width determines dwell, which is not adjustable.

At speeds greater than 940 RPM (all speeds on Saab), the Hall Effect sending unit signals the ignition control unit to make and break current flow in the primary circuit of the ignition coil.

As the ignition control unit breaks the primary circuit through the coil, secondary voltage is released through the high tension wiring, distributor cap and rotor to the spark plugs.

The idle stabilizer is mounted on the same bracket as the Hall control unit and is wired between the distributor and the Hall control unit. It senses engine speed earlier, causing ignition timing to advance.

Advancing ignition timing causes idle speed to increase, and the Hall generator to resume its normal operation.

CENTRIFUGAL ADVANCE TEST

Connect timing light to engine. Disconnect vacuum from vacuum diaphragm. Start and run engine at idle. Check ignition timing. Gradually increase engine speed and check that ignition timing changes.

VACUUM ADVANCE TEST

Connect timing light to engine. Disconnect vacuum hose at throttle housing. Start and run engine at 2500 RPM. Check ignition timing. Connect vacuum hose and verify that ignition timing advances.

VACUUM ADVANCE PRESSURE CONTROL MECHANISM (TURBO)

  1. The pressure control mechanism prevents engine knock when turbocharger is in operation. A defective pressure control system may result in reduced turbocharging pressure. Test system as follows.
  2. Disconnect distributor vacuum hose from throttle housing. Connect Tester (83 93 514 ) and hand-held air pump to hose. Start and run engine at idle speed. Check ignition timing. Apply 7.2 psi to distributor diaphragm. Check that ignition timing retards 3-7°.

IGNITION SYSTEM TEST

  1. Make sure battery is fully charged and that there is fuel in tank. Remove any spark plug wire and connect test spark plug to wire. Test spark plug must have electrode gap set at 0.16" (4 mm). Make sure spark plug is well grounded.
  2. If no spark is present, go to step 9). If spark is present, check ignition timing and adjust if necessary. Check fuel system to ensure that engine is receiving sufficient fuel. If not, repair fuel system.
  3. If fuel system is okay, rotate ignition control unit around ground bolt until fuse is visible from side. Pull cover away from fuse, but DO NOT remove fuse.
  4. Connect voltmeter between terminals 2 and 4 and turn ignition on. Voltmeter should indicate battery voltage. If reading is incorrect, check wiring between ignition switch and control unit. Repair wiring as required.
  5. If voltage is correct, turn ignition off and disconnect wiring at ignition coil. Using a ohmmeter, measure primary winding resistance between coil terminals 1 and 15. Reading should be 0.52-0.76 ohms.
  6. Measure resistance between coil tower and negative terminal 1 to obtain coil secondary winding resistance. Reading should be 2500-3500 ohms. If coil resistance is incorrect, replace ignition coil.
  7. If coil resistance is correct, reconnect coil terminals and disconnect wires from distributor. Connect a voltmeter between coil terminals 1 and 15 and turn ignition on.
  8. Voltmeter should drop from about 6 volts to zero volts within 1-2 seconds. If not, replace control unit. If voltage drop is correct, the engine should start. Ignition system is NOT at fault.
  9. Check distributor rotor, cap, spark plug wires and spark plugs. Ignition coil wire resistance should be 500-1500 ohms. Spark plug wire resistance should be 2000-4000 ohms. Distributor rotor resistance should be 1000 ohms.
  10. Check for spark across test spark plug (step 1). If spark occurs, rotate ignition control unit around ground bolt until fuse is visible from side. Pull cover away from fuse, but DO NOT remove fuse.
  11. Connect voltmeter between terminals 2 and 4 and turn ignition on. Voltmeter should indicate battery voltage. If reading is incorrect, check wiring between ignition switch and control unit. Repair wiring as required.
  12. If voltage is correct, disconnect wiring from distributor. Check voltage at connector's positive and negative terminals. If battery voltage is not present, check wiring between distributor and control unit. If wiring is okay, replace control unit.
  13. If battery voltage is present, connect voltmeter between terminal 6 and 3 on control unit. DO NOT remove fuse. Remove distributor cap and dust cover. Crank engine until any aperture of trigger wheel is in gap of Hall Effect sending unit.
  14. Turn ignition on. Voltage should be 0.4 volts or less. If voltage is incorrect, Hall Effect sending unit is defective. Replace distributor. If voltage is correct, crank engine until any trigger wheel blade enters Hall Effect sending unit gap. (Scheme 1)
  15. Voltage should now be 1.0 volts or more. If voltage is incorrect, Hall Effect sending unit is defective. Replace distributor. If voltage is correct, perform steps 5) through 8).

Hall Effect Sending Unit Test. Scheme 1

Scheme 1: Hall Effect Sending Unit Test
Scheme 1: Hall Effect Sending Unit Test

TROUBLE SHOOTING

Note. See TROUBLE SHOOTING - BASIC PROCEDURES article in the GENERAL TROUBLE SHOOTING section.

DISASSEMBLY

Note. The Hall Effect sending unit and trigger wheel (rotor) cannot be removed on Saab models. If problem exists, entire distributor must be replaced.