NOTE: Activation of the vacuum advance may align trigger wheel tooth and pick-up coil pole piece causing ohmmeter pointer to deflect. This deflection should not be diagnosed as a faulty pick-up coil.

Isolate 2 pick-up coil lead wires. Remove pick-up coil connector from module. Connect ohmmeter to either terminal and ground. See Fig 1. Connect pump and apply vacuum to test vacuum advance unit. Replace vacuum advance unit if inoperative. Connect ohmmeter to pick-up coil terminals. Operate vacuum pump and observe ohmmeter throughout the vacuum range.
Attach ohmmeter to one pick-up coil terminal and distributor housing. Set ohmmeter to middle scale. Operate vacuum advance throughout vacuum range. Reading should be infinite at all times. If not, replace pick-up coil. See Meter "A" in Fig 1.
Connect ohmmeter leads to pick-up coil connector terminals. Operate vacuum pump to ensure proper operation throughout vacuum range. Flex terminal wires by hand to check for possible intermittent defects in wiring or connectors. Pick-up resistance should be 500-1500 ohms. If resistance is incorrect, replace pick-up coil. See Meter "B" in Fig 1.

Fig 1: Pick-Up Coil Test Connections

Courtesy of GENERAL MOTORS CORP.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Pick-Up Coil

Use the Manual With the Right Hardware

When to See a Mechanic

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