Porsche 968 Timing Curve

Porsche 924 Turbo

Intake air distributor Control line Distributor Distributor advance Distributor retard Auxiliary air regulator Temperature switch (58 °C) Purge valve To carbon canister To fuel tank Vacuum control Vacuum booster Crankcase vent

Vacuum Porsche 924 Turbo

Tank Vent Control

Purge Valve

Vacuum opens purge valve (13). A temperature switch (10) surrounded by engine coolant is installed in a control line leading to the purge valve. The temperature switch opens at a coolant temperature of 58 ± 3 °C and opens the line to the purge valve. The temperature switch closes again at 48 ± 3 °C. ^

Operation: Purge Valve

A — Fuel vapor inlet B — Fuel vapor outlet C — Vacuum line connection D — Spring-loaded valve plate E — Diaphragm F — Orifice bore

Engine Cold (coolant temperature below 58 °C)

The temperature switch is closed. No vacuum goes to the purge valve regardless of operating conditions, because the valve is closed. Tank vent vapors are trapped in the carbon canister.

Engine Warm (coolant temperature above 58 °C)

The temperature switch is open. The purge valve remains closed when engine is stopped, running at idle speed or full throttle. The purge valve is opened by vacuum in partial throttle range. Tank vent vapors are drawn off by the engine.

Systeme Injection Porsche 924

1 — Carbon canister

2 — Expansion tank

6 — Pressure reservoir

7 - Fuel filter

8 — Fuel distributor

9 — Fuel injection lines

10 — Temperature switch

11 — Intake air distributor

(with built-in orifice)

15 — Vacuum control line

Transistor Ignition System with Hall Sender

The engines for USA and Canada cars have an ignition system with a Hall sender and hybride solid state control unit.

The hall ignition system is breakerless and when combined with idle stabilizer reduces the need for timing and idle speed adjustments.

The operation of the Hall sender is based on the Hall principle: that is, if a constant amount of current flows through a semi-conductor layer and the layer is exposed to a magnetic field, a small voltage will be generated. This Hall voltage is used as control pulses to trigger the ignition control unit.

924 Turbo Trigger

1 - Shutter

3 — Permanent magnet

4 — Clearance a — From or to control unit for idle stabilization b — To ignition control unit

Design of Distributor with HALL Transmitter

The HALL sender (2) and a permanent magnet are mounted on the distributor baseplate with a space between them. This provides clearance (a) between the magnet and HALL sender. Guide plates (5) on the magnet and HALL sender permit the building up of a closed magnetic field (magnet-guide plates-HALL sender-magnet) — thus producing a magnetic field (4).

A shutter (1) connected with the distributor rotor moves through clearance (a) of the magnetic field when the engine is running. The shutter has as many equally spaced openings as there are cylinders in the engine.

Force Cylinder Magnetic


If the shutter (1) is in the area of the magnetic field (4), the magnetic lines of force will be diverted by the shutter and not have an effect on the Hall layer of the Hall sender. The Hall sender stops generating the Hall voltage. The final stage of the ignition control unit becomes conductive and primary current flows through the ignition coil.

1 - Shutter

3 — Permanent magnet

4 — Magnetic field

As soon as the shutter (1) leaves the magnetic field (4), i. e. the shutter opening moves into the magnetic field, the magnetic lines of force flow through the Hall layer of the Hall sender. The Hall sender transmits a Hall voltage which triggers the ignition control unit. The final stage of the ignition control unit switches off the primary current to the ignition coil, and ignition occurs.

1981 924 Turbo Ignition Coil Wireing

Repair Instructions

The ballast resistor, ignition coil and control unit of the transistor ignition systems are matched to each other. Always make sure that only specified parts are installed. Wire connections on the control unit and Hall sender must not be mixed up, since this would destroy the control unit and Hall sender.

The battery positive terminal must never be connected on ignition coil terminal 1, since this would destroy the control unit by short circuit.

Checking Operation

The operation of the Hall sender and control unit can be checked quickly as follows. Connect a voltmeter (0 to 16 V range) or a test lamp between ignition coil term. 15 and ground. Start engine and observe voltmeter or test lamp.

If voltmeter needle pulsates or test lamp flickers, the Hall sender and control unit are probably okay.


A new distributor is used in cars with Hall ignition.

Part No.: 477.905.203 Bosch Code: 0237 022 020

Ignition Curves Bosch Distributors

Verteilerwellendrehzahl in 1/min

Centrifugal Ignition Control Curve, Type 924 (USA, Canada)

Verteilerwellendrehzahl in 1/min v.OT

Porsche 964 Engine Wiring Diagram

n. OT 100 200 300 400 500 Unterdruck mbar-^

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