Porsche 924S & 944 TDC sensor bracket evolution
From 1982 to 1991, Porsche revised the TDC sensor bracket on the 924S and 944 three times. Here is what changed between each version and why it matters.
Contents
Over the years Porsche updated the TDC (top dead centre) sensor bracket on the bell housing. Between 1982 and 1991 three versions followed one another, each with a specific change.
First version (1982 - 1985)
The first version is very basic but would remain the foundation for all future versions. It is found mainly on Porsche 944s from 1982 to 1985.
It houses two sensors whose distance from the trigger wheel on the flywheel can be adjusted.
The first sensor the one closest to the engine, identified by the letter B engraved on the bracket is the top dead centre sensor. The second, identified by the letter D, is the reference speed sensor.
Second version (1986 - 1988)
From 1986 onwards, a second version appeared. The two original sensors are still present and unchanged, but a third sensor joins them.
Aligned with the top dead centre sensor, this third sensor allows Porsche to diagnose potential faults related to the TDC sensor.
This version is found mainly on the 924S and 8-valve 944.
Third version (1987 - 1991)
With the arrival of the 16-valve engine, Porsche had to fit a more powerful starter motor.
A more powerful starter motor means greater electromagnetic interference. Porsche revised the bracket again and added a shield that protects the TDC sensor. Without it, cold and hot starts are less consistent.
Going further
If you need to set the bracket and adjust the sensors, Porsche 924S & 944 speed and reference sensors: how to test, replace and adjust covers the procedure and the usual mistakes.
If hot starts remain unpredictable with healthy sensors, the mechanical DME relay is the other common cause — see the solid-state replacement in 5 affordable modifications for Porsche 924S/944.