Pickup 1997

Diagnosis & Testing


All vehicles utilize a crank angle sensor in the distributor. This sensor is used to provide engine position information to the Electronic Control Unit (ECU). The ECU regulates ignition timing electronically, therefore no vacuum or centrifugal advance is used. Also, because of the ECU control, no periodic service adjustments are necessary. However, if timing or idle speed problems are suspected a combined ignition timing and idle speed inspection procedure is provided.

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Fig. Distributor assembly with crank angle sensor

The only major component in the electronic ignition distributor assembly is the crank angle sensor. It is basically a rotor plate wheel with 360 slits, one per degree of crankshaft rotation. A Light Emitting Diode (LED) is mounted above the slits and a photo diode is below. As each slit uncovers the LED, the photo diode detects the signal and reports to the ECU. A second LED/photo diode pair is mounted inboard of the 1 degree set to read slits indicating Top Dead Center (TDC) of each cylinder, with a special signal for the No. 1 cylinder. On all engines, the assembly is in the distributor (retained by 2 screws), just below the rotor.

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Fig. Power transistor and ignition coil

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Fig. Crank angle sensor components

The ECU sends an ignition signal to a power transistor, which turns the coil primary circuit on and off. The primary circuit current is amplified by a resistor. The ignition system is a standard configuration: one power transistor firing one ignition coil, which sends the high voltage to the distributor cap.