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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.

Air mass meters, more commonly known as mass air flow sensors or MAF sensors, are devices used in vehicle engines. They are used to determine and measure the amount of air that flows into a vehicles engine. A hot wire element provides information to the vehicles on-board computer on the air flowing into the engine by becoming cooler when more air enters the engine. However, the MAF sensor can become faulty over time and provide wrong information to the on-board computer. You can check your MAF sensor regularly by performing a few tests to determine if it is functional.

Instructions

MAF Sensor Test

1

Park the vehicle on a flat surface. Turn off both the ignition and the vehicles engine. In many vehicles, turning the key in the ignition once will power the vehicles battery. This allows the user to control electrically-powered devices such as the radio. Turning the key further will power the engine to start the vehicle. In this case, turn the ignition and the engine off. Disconnect and remove the electrical connector on the MAF sensor.

2

Connect the ohmmeters positive probe on the MAF sensor terminal that is marked as "SIG".

3

Join the negative probe on the ohmmeter to the "GND" terminal on the MAF sensor.

4

Record the reading from the ohmmeter. If the reading indicates an infinite resistance or open circuit, the hot wire element of the MAF sensor is damaged.

Power Supply Test

5

Park the vehicle and turn on the vehicles ignition. Do not start the vehicles engine but ensure that the ignition is on.

6

Open the vehicles hood. Determine the location of the MAF sensor and its electrical connector. Generally the sensor is located on the intake duct on the air filter housing in the front portion of the engine.

7

Disconnect the MAF sensors electrical connectors. Join the voltmeters negative probe to the sensors GND terminal and the positive probe to the terminal indicated as "B+".

8

Record the voltage on the sensor. A voltage reading of zero indicates the MAF sensor may not be receiving any or enough electrical input from the vehicles on-board computer, which means the MAF sensor is not functioning properly. There should generally be a steady fluctuation in the voltage if the MAF sensor is functional.

Smog tests are designed to make sure vehicles are not emitting a higher than acceptable amount of exhaust into the atmosphere when they are driven. Failing a smog test can cause problems when you go to renew your vehicles registration. Some states and counties do not allow vehicles that fail a smog test to be registered until they can pass the test. Smog is fog that has been contaminated with smoke, exhaust and chemical fumes.

Good Maintenance

Keep your vehicle in good working condition. Cars tend to emit more exhaust gases when they are not running properly or are overdue for routine maintenance procedures such as oil and filter changes. You should also refrain from running low quality fuel in your vehicle right before you have an emission or smog test performed. Low quality fuel can cause your vehicle to emit more exhaust and run poorly. In some cases, such as if you believe your vehicle has bad gas in it, you may want to run a fuel additive through your vehicles fuel system prior to the smog test.

Check Engine Light

The check engine light should not be on. The check engine light indicates there is a problem with the vehicle and may cause your car to automatically fail the smog test in some locations. Therefore, you should make all necessary repairs prior to having a smog test done. If you suspect your vehicle is going to fail a smog test, you should take it to a certified mechanic and have it thoroughly checked out prior to your smog test.

Run the Car

Smog experts recommend making sure your car is thoroughly warmed up prior to arriving for your smog test. This means driving the car for 15 to 30 minutes before you take the car in to be tested. A warmed up engine will perform better. Another common suggestion is to make sure your tires are properly inflated before showing up for the test, as a low tire can effect the way your vehicle performs if the inspector has to drive the car.

Exhaust Systems and Aftermarket Components

If you live in an area with strict smog requirements, such as the state of California, it is probably a good idea not to alter your vehicles exhaust system. Aftermarket components such as catalytic converters and intake manifolds can cause your vehicle to fail a smog test or inspection. Keeping your vehicle properly functioning reduces your likelihood of failing a smog test.

Car batteries work when the chemical reactions in the battery cause electrons to gather at the negative terminal. Turning the key into the "on" position connects a circuit between the negative and positive terminal, causing the electrons to rush from the negative terminal to the positive, providing the spark necessary to power the starter engine and turn the car over. When a car battery dies, it means there is a shortage of electrons gathering at the negative terminal. Car battery chargers work by reversing the flow of electrons from the positive terminal to the negative terminal, eventually causing enough electrons to gather at the negative terminal for a quick current to run from the negative terminal to the positive terminal when the circuit is connected. Testing the effectiveness of a car battery charger requires a field experiment whereby you connect the charger to a dead or dying battery and turning it on.

Instructions

1

Clean the terminals of your battery sufficiently with a clean cloth.

2

Connect the alligator clips of your charger to the terminals of your battery. Connect the negative (black) alligator clip of your charger to the negative terminal of your battery before connecting the positive (red) alligator clip.

3

Plug your battery charger into a wall socket if it is DC/outlet powered, or turn it on if it is AC battery powered.

4

Wait two to three minutes or the specified amount of time indicated in the operators manual that came with your specific battery charger. For most car battery chargers, two to three minutes is sufficient to check whether the charger itself is functional, as it will likely charge the battery enough to turn your car over.