Snowmobile CDI Box: What They Are and Troubleshooting


A CDI box is a very important part of snowmobiles. If the CDI box in your snowmobile stops working, then you can either say goodbye to snowmobiling or you can choose to fix the problem. Through this article, you will know what a CDI box does, and you’ll discover how you can troubleshoot it.

A CDI box is an electronic ignition system controller in snowmobiles and other vehicles. CDI stands for capacitor discharge ignition. The CDI box is responsible for the spark igniting in the engine through a spark plug and ignition coil.

The CDI box works by storing electrical charges on capacitors and discharging the charges through an ignition coil so that powerful sparks get produced. Aside from controlling ignition, the CDI box controls several other electrical parts of the engine. Kindly read on to know more about the CDI box.

What is a Snowmobile CDI Box?

Snowmobile CDI box is the control unit for the ignition system of snowmobiles. CDI boxes are capable of releasing energy very rapidly. They can control the timing advance, sparks, and rev limit. CDI systems have the ability to charge faster than typical inductive systems.

A CDI box has the ability to perform excellently even while shunt resistance attempt to limit its performance.

Troubleshooting A Snowmobile CDI Box

A CDI box might stop functioning well as a result of moisture, vibration, and heat that they are exposed to in the course of snowmobiling. CDI boxes don’t develop faults easily, but when they do, an inexperienced person will find it hard to trace the problem source.

The major reason why a faulty CDI box seems hard to detect is that the symptoms that you will get from a faulty CDI box are exactly the symptoms that other units of the ignition system will give when they become faulty.

An easy way to confirm a faulty CDI box is to eliminate all other units until you have only the CDI box remaining. Follow the procedures below to see how you can easily eliminate other units and confirm a faulty CDI box.

Check the battery

You need to verify your snowmobile’s battery is delivering enough current. You need a multimeter for this test. Disconnect the battery from the snowmobile and connect your multimeter to its terminals to check whether you have up to 12v. If you have up to 12v, you still need to test the battery again while it’s loaded.

I prefer to use a Fluke MultimeterOpens in a new tab. (link to Amazon) but any decent multimeter will do.

Use the battery to supply power to a device and measure its voltage. The battery is damaged or requires recharging if the voltage reduces below 10.8v. Snowmobiles require a steady voltage and current from the battery to start, so you shouldn’t suspect the CDI box if the battery is bad.

Here’s a quick video explanation for checking the battery:

Check the stator

Stator supplies extra energy to the battery and the ignition system. If the stator becomes faulty, it will give symptoms that are similar to that of a faulty CDI box. A multimeter can help you to identify a faulty stator. Set a multimeter to ohms reading and use it to test the three tabs of the stator.

  • Test only two points of the tabs at a time.
  • If all the three terminal tabs have a resistance below 1 ohm, it means the stator is probably in good condition.
  • You should proceed further to check whether the stator has no ground connection.
  • Do this by connecting the black test lead to the battery’s negative terminal and the red test lead to the stator’s terminal.

The multimeter shouldn’t read anything if the stator is good, so this test will assist you in identifying a faulty stator. You can suspect the CDI box for fault only when the stator isn’t faulty.

Here’s a video with some further explanation of stator testing:

Check the spark plug

You also need to be sure that the spark plug isn’t the source of the problem making you suspect the CDI box. Remove the spark plug cap and inspect the spark plug for damages. The spark plug is damaged if you notice corrosion, cut, or thick dark coatings on the electrodes.

If you can’t notice any damage on the spark plug, you should go further to test the kind of spark it produces. To make the spark plug produce sparks, you need to pull it outside while the spark plug cap is still attached to it. Ground the plug to the snowmobile’s frame and attempt to start the engine.

If the spark plug gives out blue sparks, then it’s in good condition. If it gives out yellow sparks or no sparks, then the plug is bad. It would help if you check the spark plug cap if the spark plug doesn’t produce any spark. Inspect the spark plug caps for corrosion and cracks.

I like to replace spark plugs often anyway. So if you suspect something wrong with a spark plug, I’d just replace it without question.

You can also use a multimeter to confirm the state of the spark plug cap. Set the multimeter to read ohms and measure the resistance of the cap. The spark plug cap is faulty If its resistance is higher than 10k ohms.

Check the main fuse

The main fuse connects the battery to the electrical units in your snowmobile, so the CDI box won’t work if the main fuse is blown. The main fuse can break or blow due to excessive vibration, old age, or electrical fault in the circuit.

It is always best to verify whether an electrical fault is not the cause of a blown fuse. Check the electrical wiring and insulations. If you observe damaged insulation, accidental grounding, or any other fault, then you have to fix such a fault before you replace the fuse.

Check the ignition coil

The ignition coil works like a step-up transformer. It accepts voltage from the CDI box and raises it to a high value that can create sufficient sparks for ignition. So if you are not getting strong sparks, the fault can either come from the CDI box or the ignition coil.

To test the ignition coil, you should carry out these steps:

  • Use an electrical wrench to detach the two ends of the coil.
  • These two ends are the negative and positive terminals.
  • Set the multimeter to ohms reading and connect its red lead to the positive terminal of the coil.
  • Use the black lead to touch the mounting bracket of the coil.

You will obtain an infinite resistance reading if the coil is not shorted. You should replace the coil if it’s shorted. If the coil is not shorted, you should proceed to test the resistance between its terminals.

Connect the leads to the positive and negative terminals of the coil and check the reading. The resistance is within good range only when it’s not higher than 1 ohm.

Here’s a quick walk through video to test ignition coils in snowmobiles:

Check the rectifier/regulator

Just like the name implies, this part of the snowmobile rectifies and regulates voltage. If the rectifier/regulator is faulty, power will become irregular throughout the electrical system.

Irregular supply of power is also one of the symptoms of a faulty CDI box, which is why you need to check this part. You can check the state of a rectifier/regulator using the diode function of a multimeter.

Here are the steps you should take to test a rectifier/regulator:

  • While your multimeter is in diode function, you should connect the positive lead to the positive diode.
  • After that, you should connect the negative lead to the stator’s inputs one after another.
  • The multimeter should read nothing or it should display OL, which means open circuit.
  • This test is a way to verify whether the diode is blocking current from traveling backward through it.

Now that you have tested the reverse bias of the diode, the next thing to test is its forward bias. To do this, you should connect the negative lead to the positive diode. Thereafter, you should connect the positive lead to the stator’s inputs one after another.

The meter should read something now, indicating that the diodes are allowing electric current to flow through them in the proper direction.

Watch out for ground wires

Overheating can destroy the electrical insulation of some wires, and thereby lead to faulty ground. When this happens, the entire electrical component in your snowmobile may stop working.

The solution to a faulty ground isn’t hard at all. You simply need to trace all the wire connections and insulate any faulty ground you come across. 

CDI box

While a multimeter alone is not enough to test a CDI box directly, all the tests that we have mentioned above are enough to prove whether the CDI box is faulty or not. If the ignition system of your snowmobile is misbehaving while all the components above are in good condition, then the CDI box in your snowmobile is faulty.

Replacement is the guaranteed solution to a faulty CDI box. So if you have a fault in your CDI box, you should replace it immediately.

Rob

That's me sinking another ATV. I love to ride no matter what it is, snowmobiles, four wheelers, dirt bikes, and anything else off-roading. I've experienced my fair share of machines, and like to share that experience here.

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