How to test a CDI box with a multimeter

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Capacitor discharge ignition, also known as CDI is a trigger mechanism with coils covered with a black box equipped with capacitors and other circuitry. Furthermore, it is an electrical ignition system that is often available in motorcycles, outboard motors, chainsaws and lawnmowers, among other electrical devices. CDI is designed to overcome long charging times which is often associated with inductance coils.

You can use a multimeter to test and assess the status of your CDI box. In this article, we shall be discussing how to test a CDI box with a multimeter.

CDI box testing procedure

When carrying out diagnosis on a CDI, using a multimeter is essential in determining a problem. You might as well use the oscilloscope in carrying out more complex test; however, very few individuals have access to this device.

Under the seat of your motorcycle, you will find a connector with a blue and white wire coming straight from the stator and going to the CDI box. Ensure that you test the side that comes from the stator rather than the side heading to the CDI box. Your multimeter should be set at 2k ohms resistance. Once this is done, measure the resistance between a blue wire to white wire and then the white wire to the ground. The blue wire to white wire resistance should be between 77 and 85, while the white wire to the ground should be 387 and 487.

When the result is not within this spec, you should consider heading over to the stator and assess whether the problem lies within it. However, when the resistances of the wires are within the recommended spec, you should reconnect the blue and white connectors. You will find a yellow, white and black with white-stripe cables coming from your CDI box heading towards the front of your bike.

Ensure you multimeter read DC volts and it is set within the range of 250. Clamp the black probe of your multimeter to the ground and then test in turns the yellow and pink wires by pressing the probe at the end of the cables. While doing this, you should try to crank your bike for some few seconds. You will not receive a steady reading; however, you should receive a minimum of 150v DC flicker on your multimeter that is if the CDI box is working accordingly.

When both sides are working accordingly, you should consider testing the wire with black and white stripes and ensure that the killswitch is running. When you fail to acquire the same result, then probably the killswitch is shorting to the ground.

If your bike fails to stop when you hit the killswitch, you should disconnect the black and white stripe wire while your bike is still running and ground it. If your bike fails to stop immediately, the chances of your CDI box being faulty are high.

Assessing for fault in your CDI

CDI is like a computer, and it helps control your motorbike; therefore knowing whether it is faulty or not is essential. Since it controls fuel injector and sparks plugs, CDI is responsible for making your motorbike operate accordingly. There are various reasons that might cause your CDI to become faulty, including aging as well as a defective charging system.

Since CDI is linked to the ignition, you will experience minimal trouble with your ignition when the CDI is in a good state. This is because CDI is responsible for storing spark power on the spark plug in your motorbike.

Diagnosing CDI is not that easy since the faulty symptoms which are observable on your CDI box might lead to a different direction. At times a faulty CDI may fail to cause a spark at all. Furthermore, when a CDI box is about to become defective, it will lead to misfires, rough running, and ignition problems as well as stall the motor.

The above mentioned faulty symptoms might be confusing; therefore, you will need to be extra careful before coming into conclusion on the problem affecting your CDI box. When your fuel pump is faulty, or the coil pack and spark plugs are faulty, you will experience the same type of faulty symptoms. Therefore, using a multimeter as a diagnostic, too while assessing the state of your CDI box is critical.

Taking good care of your CDI box

Your motorbike will only serve you well if you take good care of your CDI box and other critical parts. Furthermore, understanding how a CDI box operates will aid you to take care better care of it by assessing any faulty symptoms displayed by your CDI box. Often CDI box features a brief charging period with an incredible quick increase in voltage. It also features a short spark time.

When you overwork your CDI box, it will not serve you for an extended period. Among the advantages of a CDI box is that it is not sensitive to shunt resistance. However, the CDI box does not provide ample ignition efficiency since it features a relatively short spark duration.

As a motorbike owner or lover, you should probably understand that a CDI box model is either an AC or DC. These two types of CDI model operate differently; therefore, it is essential to have your motorbike assessed by a professional in order to identify which make is ideal for you.

Why is the CDI box essential?

For your motorbike to function accordingly, you will require having a CDI box that if fully functional. CDI box feature various advantages in your motorbike such as;

Charges within a short period. This is one of the significant benefits of a CDI box, making it ideal for application where time is critical.

Short transient response. CDI features a fast voltage rise which is between 3 and 10 kV/ µs when compared to the inductive system, which is between 300 and 500 V/ µs. Furthermore, it has a short spark duration of approximately 50 to 80 µs.

Shunt resistant. This is associated with fast voltage rising in the CDI box system.


By now we hope that you have understood clearly how to test CDI box using a multimeter as well as its advantages and how the CDI box operates. You should always take care of your CDI box and assess for any faulty symptoms for it to work accordingly for a longer period.

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