How to Test a CDI Box with a Multimeter (Three Step Guide)
Content
CDI means capacitor discharge ignition. The CDI coil trigger sports a black box lid filled with capacitors and other electrical circuits. This electric ignition system is mainly used in outboard motors, lawn mowers, motorcycles, scooters, chainsaws and some other electrical devices. Capacitor discharge ignition is designed to overcome problems associated with long charging times.
In general, to check the CDI box with a multimeter, you should: Keep the CDI still connected to the stator. Measure using the stator end instead of the CDI end. Measure blue and white resistance; it should be between 77-85 ohms and the white wire to ground should be between 360-490 ohms.
Internal CDI Operations
Before we learn about the different ways to test CDI boxes, you might be interested in learning about the inner workings of your CDI ignition. Also called thyristor ignition, CDI stores an electrical charge and then disposes of it through the ignition box to make it easier for the spark plugs in a gasoline engine to create a powerful spark.
The charge on the capacitor is responsible for providing ignition. This means that the role of the capacitor is to charge and discharge at the very last moment, creating sparks. CDI ignition systems keep the engine running as long as the power source is charged. (1)
Symptoms of CDI malfunction
- Engine misfiring can be blamed for several things. A worn ignition box found inside your CDI module is one of the most common causes of engine misfiring.
- A dead cylinder can prevent the spark plugs from firing properly. Fuzzy voltage signals may be due to a bad blocking/forward diode. If you have some dead cylinders you can check your CDI.
- Failure occurs at RMPS 3000 and above. While this could indicate a stator problem, experience has shown that a bad CDI can also cause the same problem.
Now let's learn how to check the CDI box with a multimeter.
You will need a CDI box and a multimeter with pin leads. Here is a XNUMX step guide to testing the CDI box.
1. Remove the CDI unit from the electrical device.
Let's say you're working on your motorcycle's CDI unit.
Your motorcycle's CDI unit is no doubt connected to insulated wires and pin headers. With this knowledge, removing the CDI unit from a motorcycle, chainsaw, lawn mower or any other electrical device you are working with is not difficult.
Once you've managed to remove it, don't work on it immediately. Leave it alone for about 30-60 minutes to allow the internal tank to release the charge. Before testing your CDI system with a multimeter, it's best to do a visual inspection. Pay attention to mechanical deformations, which manifest themselves as damage to the casing insulation or overheating. (2)
2. Testing CDI with a multimeter - cold test
The cold test method is designed to test the continuity of the CDI system. Your multimeter must be in continuous mode before you start the cold test.
Then take the leads of the multimeter and connect them together. The DMM will beep.
The goal is to establish the presence/absence of continuity between all ground points and numerous other points.
Determine if you hear any sounds. If your CDI unit is working properly, you should not hear any sounds. The presence of beeps means that your CDI module is faulty.
The presence of continuity between ground and any other terminal means the failure of the trinistor, diode or capacitor. However, not all is lost. Contact a professional to help you repair the failed component.
3. Testing the CDI Box with a multimeter - hot test
If you choose to use the hot test method, you do not need to remove the CDI unit from the stator. You can test with the CDI still connected to the stator. This is much easier and faster than the cold test method where you have to remove the CDI box.
Experts recommend measuring continuity with a multimeter through the end of the stator, not the end of the CDI. It is not easy to connect any test lead through the connected CDI unit.
The good news is that continuity, voltage and resistance are the same as at the end of the stator.
When conducting a hot test, you should check the following;
- The resistance of blue and white should be in the range of 77-85 ohms.
- The white wire to ground should have a resistance range of 360 to 490 ohms.
When measuring the resistance between the blue and white wires, remember to set your multimeter to 2k ohms.
You should be concerned if your resistance results are not in these ranges, in which case make an appointment with your mechanic.
A multimeter is a useful tool for accessing and checking the health status of the CDI box. If you don't know how to use a multimeter, you can always learn. It's not difficult and anyone can use it to measure resistance and other parameters it was designed to measure. You can check out our tutorial section for more multimeter tutorials.
Confirming that the CDI unit is working properly is critical to the functioning of your motorcycle or any other electrical device. As before, CDI controls fuel injectors and spark plugs and is therefore an important component in the proper functioning of your electrical device.
Some causes of CDI failure are aging and a faulty charging system.
Security
Working with CDI systems should not be taken lightly, especially if you are unknowingly dealing with bad CDI. The mechanical parts of the motorcycle and other devices must be handled with care.
Use standard personal protective equipment such as cut-resistant and waterproof gloves and goggles. You don't want to deal with electrical injuries due to not following safety precautions.
Even though the capacity and active components inside the CDI box are minimal, you still need to be careful.
Summing up
The above two approaches to testing CDI blocks are efficient and practical. Although they differ even in terms of time spent (especially because one method requires the removal of the CDI box), you can choose which one is most convenient for you.
Also, you need to analyze the result, because what you do next depends on your analysis. If you make a mistake, for example, if you cannot recognize an existing problem, the problem will not be solved quickly.
Postponing necessary repairs can cause further damage to your DCI and related parts and generally ruin your experience with your motorcycle, lawn mower, scooter, etc. So, make sure you get this right. Do not hurry. Do not rush!
Recommendations
(1) ignition systems - https://www.britannica.com/technology/ignition-system
(2) mechanical deformations – https://www.sciencedirect.com/topics/
materials science/mechanical deformation
