TSZi-S Transistorized Ignition System - Description
85bmw05GROUP 12 Engine - Electrical
Bulletin Number 12 02 85 (2037) Page 1 of 3
Montvale, NJ April 1985 Technical Dept.
SUBJECT: TSZi-S Transistorized Ignition System
MODEL: 318i
The TSZi-S transistorized ignition system is a new development with the following innovations:
- waterproof plug connections
- integrated heat sink
- starting ignition timing angle for optimum starting behavior (TSZi-S)
- TD (Trigger Diode) signal as a replacement of the signal from terminal 1 (of the ignition coil) for activating the tachometer or L-Jetronic control unit.
- with engine not running, but ignition key ON, coil circuit is not closed (like MOTRONIC) thereby preventing coil overheating.
Studies have shown that, for optimum starting on a four (4) cylinder engine, the ignition timing angle should be close to top dead center. Therefore, a special starting function has been integrated into the TSZi-S control unit to ensure good starting behavior over the entire temperature range.
The operation of the circuit is shown graphically here where:
(1) Track of ignition timing curve with starting function (broken line)
(2) Normal timing curve (solid line)
Starting is activated via terminal 50 as long as the starter is operated. As soon as the engine has started and the ignition lock goes back to terminal 15, the timing angle is moved into the area of normal engine idle timing. Above idle speed, normal centrifugal and vacuum timing takes place.
The control unit processes the signal of terminal 1 into a square wave as opposed to the previous primary circuit spike.
The TD signal is used for:
rpm - tachometer, service indicator, instruments rpm - switch idle - control L - Jetronic, fuel shut-off (overrun)
The TD connection has been introduced on the TSZi-S system for interference suppression. The square-wave signal shown here is easier to process electronically and emits no interference as opposed to the signals of terminal 1.
In the current version, terminal 1 only connects the TSZi-S control unit with the ignition coil and the diagnosis plug.
L-Jetronic control units with TD signal cannot be replaced by standard units which are designed to use the "spike" type of signal of coil terminal 1.