AUTOMOTIVE ELECTRICAL CIRCUITS AND WIRING
AUTOMOTIVE ELECTRICAL CIRCUITS AND WIRING
AUTOMOTIVE ELECTRICAL CIRCUITS AND WIRING
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ELECTRONIC IGNITION DISTRIBUTOR SERVICE<br />
Most electronic ignition distributors use a pickup coil to sense trigger wheel rotation<br />
and speed. The pickup coil sends small electrical impulses to the ECU. If the<br />
distributor fails to produce these electrical impulses properly, the ignition system can<br />
quit functioning.<br />
A faulty pickup coil will produce a wide range of engine troubles, such as stalling, loss<br />
of power, or not starting at all. If the small windings in the pickup coil break, they will<br />
cause problems only under certain conditions. It is important to know how to test a<br />
pickup coil for proper operation.<br />
The PICKUP COIL OHMETER TEST compares actual pickup resistance with the<br />
manufacturer's specifications. If the resistance is too high or low, the pickup coil is<br />
faulty. To perform this test, connect the ohmmeter across the output leads of the<br />
pickup coil. Wiggle the wire to the pickup coil and observe the meterreading. This will<br />
assist in locating any breaks in the wires to the pickup. Also, using a screwdriver,<br />
lightly tap the coil. This action will uncover any break in the coil windings.<br />
Pickup coil resistance varies between 250 and 1,500 ohms, and you should refer to the<br />
service manual for exact specifications. Any change in the readings during the pickup<br />
coil resistance test indicates the coil should be replaced. Refer to the manufacturer's<br />
service manual for instructions for the removal and replacement of the pickup coil.<br />
Once the pickup coil has been replaced, it will be necessary to set the PICKUP COIL<br />
AIR GAP. The air gap is the space between the pickup coil and the trigger wheel<br />
tooth. To obtain an accurate reading, use a NON-MAGNETIC FEELER GAUGE<br />
(plastic or brass).<br />
With one tooth of the trigger wheel pointing at the pickup coil, slide the correct<br />
thickness non-magnetic feeler gauge between the trigger wheel and the pickup coil.<br />
Move the pickup coil in or out until the correct air gap is set. Tighten the pickup coil<br />
screws and double-check the air gap setting.<br />
Ignition Timing<br />
The ignition system must be timed so the sparks jump across the spark plug gaps at<br />
exactly the right time. Adjusting the distributor on the engine so that the spark occurs<br />
at this correct time is called setting the ignition timing. The ignition timing is normally<br />
set at idle or a speed specified by the engine manufacturer. Before measuring engine<br />
timing, disconnect and plug the vacuum advance hose going to the distributor. This<br />
action prevents the vacuum advance from functioning and upsetting the readings.<br />
Adjustment is made by loosening the distributor hold-down screw and turning the<br />
distributor in its mounting.<br />
<strong>AUTOMOTIVE</strong> <strong>ELECTRICAL</strong> <strong>CIRCUITS</strong> <strong>AND</strong> <strong>WIRING</strong> 71/ 101