Last Updated on October 22, 2023 by Kevin Chen
Image source Mr Fix It Ca
A CDI box is an important component in motorcycles, though some vehicles also have it.
You are also to find this box in lawnmowers, turbine-powered aircraft, chainsaws, and other devices that have small engines.
The acronym CDI stands for capacitor discharge ignition and is the main functional body for the ignition system. Since its invention, it has evolved to replace the mechanical ignition process in most engines.
A CDI can develop mechanical and electrical faults like any other engine component. When this happens, you will have to diagnose the CDI box and find the right solution.
In this guide, we will break down the steps you should follow when testing a CDI.
How a CDI works?
Before we get into the process of testing a CDI, it will be prudent to know how it works.
The general working principle of a CDI entails the storage of the electrical energy in the capacitor. It will then discharge this energy to the ignition coil and be used to create a spark.
To make things clear, here are the steps that explain the working mechanism of the CDI.
- Charging: The whole process starts with charging the capacitor. Usually, this happens when the engine of the vehicle is running and the CDI will charge the capacitor to the fullest. In most cases, the maximum power will be 400 volts.
- The second step is all about the triggering process. Here, a trigger signal detects the state of the engine to determine the perfect timing to discharge the capacitor. This signal is sent to the silicon-controlled rectifier (SCR) which is designed to allow the flow of electric current in one direction.
- The next step entails the discharge process. The signal that was generated in the previous step will cause the CDI to discharge the capacitor. The discharged energy from the capacitor will be channeled to the ignition coil. This energy will be responsible for creating a spark that will ignite the engine.
- The last process is recharging. Here, the CDI will recharge the capacitor in readiness for the next ignition process.
Tools and equipment for testing CDI
The main tools that you will need for the job include:
- CDI box that you suspect has been damaged and need to be tested
- Multimeter which in this case will serve as our main testing tool
I assume that you already know how to use a multimeter.
Now let’s discuss the steps to follow when testing CDI.
Step 1: Remove the CDI from its position
The position of a CDI usually varies from one machine to another. If you are dealing with a motorcycle, the CDI is beneath the bike’s seat, and in some bikes, it is next to the side covers.
For the vehicles, the CDI box is near the ignition coil or just near the battery. Refer to the vehicle’s manual to find the exact location of the CDI box. You can also check out online material for reference.
Before you remove the CDI box, first ensure that the engine is off. Disconnect the wires that link the CD to the starter the proceed to unmount the box.
After the disconnection, leave the CDI for at least 30 minutes. This will allow it to discharge the internal charges. You should be able to carry out a visual inspection of the CDI box so that you can detect any physical damage.
Step 2: Carry out cold test on the CDI box
The purpose of the cold test is to determine the continuity of the CDI box components. The good news is the box does not have many components so doing a cold test will be an easy job.
How do I carry out the cold test or continuity test on the CDI box?
This one is simple, Just set the multimeter to the continuity mode then connect the probes between different points of the CDI components.
A beeping sound from the multimeter is an indication of continuity. This shows that there is no problem with the CDI box.
No beeping sound is a sign of a problem in the CDI box. You need to find out the exact problem with the connections and fix it.
Probably the issue could be with the capacitor, SCR, and even diode. Damage on any of these electronic components will interfere with the continuity, which will also prevent the smooth flow of current.
Step 3: Run a hot test on the CDI box
After determining the continuity issue, you will have to do further testing on the CDI box using the same multimeter.
Hot test majorly entails finding the resistance value on different sections and components of the CDI box.
You will test the resistance between the stator and the CDI.
To do this, set the multimeter to the resistance setting, and to be precise, 2k ohms. You can then connect the multimeter probes between the starter and the connection point of the CDI.
Take note of the readings on the multimeter. Any change in the reading is an indication of a well-functioning CDI box. If there are no changes in the readings means that the multimeter CDI box is damaged.
Signs of a damaged CDI box
How do I know my CDI is damaged?
Even before you decide to test the CDI box, there are signs that will point towards a damaged CDI, whether it is on a vehicle or any other machinery. These signs include the following.
- Engine stalling
- Misfiring engine
- Hard staring engine
- Backfiring engine
- An array of ignition issues
- Dead engine cylinder
- Misbehavior of the tachometer.
While these symptoms point towards damaged CDI, you should also explore the possible damage on other issues on the vehicle. Some of the issues could be due to the damaged stator or even the ignition coil.
A CDI will always be an integral component of a vehicle’s ignition system. Testing it will always be the surest way to ensure that it is in perfect condition. In case of a damaged electronic component in the CDI box, consider doing a replacement.
You should also involve a professional electrician if you are not sure of how to do the CDI box testing.
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