90 Quattro 20V (Canada) L5-2309cc 2.3L DOHC (7A) (1989)
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MPI Start-Up Reference Signals
The engine speed sensor signal is also used to calculate the position of the crankshaft at any given time. The flywheel has 135 teeth around its
circumference. Each tooth generates a pulse when it passes the speed sensor, representing 2.6° of crankshaft rotation. Once TDC for the #1 cylinder is
established (by the crankshaft position reference sensor), the ECU counts the number of flywheel teeth that pass the sensor, and continuously calculates
the position of the crankshaft, to determine ignition and injection timing for each cylinder.
SELF DIAGNOSIS
The ECU will recognize the absence of a signal and store a fault code, indicating an open or shorted sensor or sensor circuit. There is no plausibility
check for this input, however, the ECU uses this signal, along with the signal from the air mass sensor, to check the plausibility of the idle switch signal.
There is no substitute signal for this sensor. If the engine speed sensor fails or the signal is lost due to a wiring problem (open or shorted wire), the
engine will not start or run. If the sensor signal is corrupt or intermittent, the engine may or may not start, but will run very poorly if it does start.
