If ever you have faced starting issues in your scooter, lawnmower, outboard motors, and many other electro mechanical devices? If yes, then next time your first step after testing the battery should be to test its cdi box. A CDI or “capacitor discharge ignition system” is called by many other terms like a black box, pulse pack, and brain box. All motorbikes after 1980’s come with this cdi box for an efficient ignition system.
The good news is that we are going to tell you how to test cdi box with multimeter in some simple steps. So you may test it and most probably fix or replace it by yourself before going to some mechanic garage.
Things to do before analyzing a cdi box
- First of all, arrange a reliable electronic or automotive voltmeter, and do a self checking test to verify its functions like voltage and resistance.
- Now you have to search cdi box from the bike or other device circuitry. You can easily identify it by looking for a block box in the circuit box. It’s usually connected with wires and connectors around it.
- As this device has capacitors with charge stored in them, wait for some time like 20 to 30 minutes so its internal capacitance is completely discharged.
Testing cdi box with Multimeter
Doing a physical checking
- We will suggest inspecting cdi box physically after disconnecting it from the stator before doing a troubleshoot with a multimeter, and check for any physical damage, debris, spark sign, or other issues.
Test 1 (Continuity test)
- For this type of test keep your meter in continuity mode, and do self test by connecting the multimeter’s leads with one another. If a beep sound is produced that means the meter is working properly.
- Now connect one lead of multimeter with the ground and other to various points of cdi box to test continuity.
- There should be no continuity between ground and box, it means no beep sound should be produced if you have a dmm with a specific continuity function.
- If ever you hear a beep sound along any of cdi points and ground that will mean either cdi box or some part of it is faulty.
- Continuity means a short path between two physical points, so every beep would be a sign of short in cdi box.
Test 2 ( Hot test)
- First of all switch, your digital multimeter to resistance mode set it at 2k ohm.
- Now connect the meter to white and blue wires and check resistance, it should be roughly between 75 to 86 ohms.
- After that connect one lead of the meter to white wire and other to the ground at the same time and check result on screen, it should be 350 to 500 ohms approx.
- If your results are noticeably different by these mentioned ranges then we suggest you go for some auto mechanic for more inspection.
Signs of a failed CDI
There are some signs and symptoms by which you can assess whether the cdi has failed or one of its parts is malfunctioning.
- If one or a number of cylinders are not firing properly. It might be due to some defective diodes of cdi. A defected cdi diode can produce a distorted voltage signal which can deteriorate the plug’s firing process.
- A misfiring engine is another common symptom of a failed cdi, a damaged ignition coil of cdi box may be a reason behind it.
- Backfiring is also a sign of defective CDI.
You can check cdi box status by performing these simple steps which are given above. But for that, you must know how to use a multimeter for basic electrical tasks. If you don’t know much about it you may follow the link given above to learn about using digital multimeters.
A motorbike, lawn mower, or other automotive’s ignition system mainly depends on capacitor discharge ignition system. So it should be in good condition to avoid any starting issues. We also advise you not to ignore problems when they are at initial stage like delay in cranking etc. in fact these symptoms tell us to repair our machinery as soon as possible.
Leo Maxwell is basically an Electrical engineer and hobby tech writer, having 13 years of experience in the electronics and instrumentation industry. He has hands on experience working in various fields like Powerhouses, solar, automotive, and FMCG.
During his career, he has used many power tools and meters in electrical projects. Now his aim is to explain tools and troubleshooting in easy guides to help people. Other then it, leo loves traveling, reading books and DIY tasks.