Tacho and Crank

[julian64]

Both of these signals come to the engine management unit.

I believe the crank signal comes from a mutlitoothed wheel in the bellhousing, but no idea where the tacho signal into the ECU comes from.

Anyone able to enlighten me with the answer, or even better how the ECU uses them?

Neither currently make sense to me as a TDC signal.

The crank signal is a a 1.1KHZ sinewave at 1000rpm.
The tacho is a 75Hz squarewave at 1000rpm.

[Peppe]

Hi !

The crank signal is used by the ECU to control TDC and engine rpm. The signal to the tacho is a output signal from the ECU to the tacho.

//Peppe

[ridds]

RPM toothed wheel on teh crank will have a tooth missing which will tell the ECU where TDC is. Usually 60-1 or similar.

[GreenV8S]

Isn't the tacho signal an OUTPUT from the ecu?

[julian64]

Damn, I thought the tacho signal was an input not an output from the ecu

[ridds]

Crank to ECU, ECU to tacho. Pin 33 from the ECU to be precise.