Pick-Up Coil: Description and Operation

Optical Distributor Cut Away View:

LOCATION
Housed in distributor.

PURPOSE
The Powertrain Control Module (PCM) uses this input to determine engine speed and crankshaft position, and adjusts ignition timing, fuel injection, and idle speed accordingly.

OPERATION
A thin disk, with 2 sets of slots, spins at half engine speed, between two LED and photo diode pairs (optical sensors).

Generates pulses when slots pass between Light Emitting Diodes (LED's) and photo diodes.

High Data Rate Slots
The outer or "high data rate", slots pass through the corresponding optical sensor 1 slot per 2 degrees of crankshaft rotation.

This high data rate, set of slots is used for ignition timing for engine speeds up to 1200 rpm, where speed changes due to individual firing pulses are significant, to increase timing accuracy.

Low Data Rate Slots
The inner, or "low data rate", set of 6 slots, correspond to top-dead-center for each piston.

The low data rate, set of slots is used to trigger the fuel injection system, and ignition timing for engine speeds above 1,200 rpm, where speed changes due to individual firing pulses are small.

NOTE: If the PCM does not detect input from the pick-up, the PCM de-activates the ASD and fuel pump relays, interrupting power to the fuel pump, fuel injectors, ignition coil, and oxygen sensor heater, preventing fuel injection and ignition, (a no start condition).