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How to Test the Ignition Coil on a 12 Volt Geo Metro

The Geo Metro, like most other passenger cars, uses a 12-volt power system to supply the cars electrical needs. Unfortunately, the cars spark plugs require much higher voltage to create the spark that ignites the fuel-air mixture. The ignition coil provides this increased voltage by converting the 12 volts supplied by the electrical system into a charge of up to 30,000 volts. Quite often, when a car uses to run or runs badly, the fault lies with the ignition coil.

Instructions

1

Locate the ignition coil, connected to the cars firewall. It is a cylindrical object with a thick wire connected to it.

2

Remove the plastic cap that protects the coil.

3

Use a voltmeter to test the coils positive terminal. Set the voltmeter to 12-volt direct current (DC), and touch the positive probe to the positive terminal on the coil. The terminals are bolts on one end of the coil, and the positive terminal will be marked with "+." The voltmeter should read 12 volts. If not, proceed to Step 4.

4

Check to ensure that the ignition coil electrical connector is firmly in place. Check the under-hood fuse panel to ensure the coil fuse/relay has not gone bad. Blown fuses of this type appear burned. Recheck the coil with the voltmeter. If it still detects no power, the problem lies at a location other than the coil.

5

Disconnect the negative battery terminal to cut off power to the coil.

6

Disconnect the high-tension cable from the coil. This is the thick wire that attaches to the center of the coil using a connector similar to a spark plug boot. Grasp the boot, and pull it straight off the coil as you twist it.

7

Use a 1/4-inch drive socket or a small box end wrench to disconnect the negative and positive terminal wires from the coil.

8

Remove the coil from the firewall by removing the two bolts that attach the mounting bracket.

9

Set the voltmeter to test resistance (ohms), and touch the probes to the positive and negative terminals. The voltmeter should read between 1.35 and 1.65 ohms for standard-emission models, and between 1.08 and 1.32 ohms for cars with upgraded (California) emissions. If the reading falls outside this range, replace the coil.

10

Check the resistance between the positive terminal and the high-tension terminal just as you did in Step 9. This resistance should lie between 22.1 and 22.9 kilohms for all models. If the reading falls outside this range, replace the coil.

Posted by Unknown at 6:15 AM

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