[ischmitz]

Loren, I disassembled most of the code for the Bosch DME's (Porsche, BMW and a few others) and the reference sensor signal will be used during engine running conditions. There is a sort plausibility logic in the code that checks signal integrity of the speed sensor and "resets" TDC location under certain conditions (jitter).

The FI2438-03 is armed every time the MCU "writes" to a certain address space in external memory. Once armed it will trigger a non-maskable interupt at TDC.

The fact that the engine will continue to run when you disconnect the reference sensor might not cause an issue during idle. But I wouldn't take the engine through the rev ranges if I were you.....