Hey guys! Today, we're diving deep into the world of the 2008 Polaris Sportsman 90 CDI box. If you're experiencing issues with your little ATV, chances are the CDI (Capacitive Discharge Ignition) box might be the culprit. Don't worry, we're here to help you diagnose, troubleshoot, and hopefully solve those pesky ignition problems. Let's get started!

Understanding the CDI Box

First things first, what exactly is a CDI box? Think of it as the brain of your ATV's ignition system. It's responsible for controlling the timing and intensity of the spark that ignites the fuel in the engine. Without a properly functioning CDI box, your Sportsman 90 won't start or run correctly.

Key Functions of the CDI Box:

• Timing: The CDI box tells the ignition coil when to fire the spark plug. This timing is crucial for optimal engine performance. Too early or too late, and you'll experience issues like poor acceleration, misfires, or even engine damage.
• Voltage Regulation: The CDI box regulates the voltage sent to the ignition coil. This ensures a consistent and powerful spark, regardless of the engine's RPM. A weak spark can lead to starting problems and reduced power.
• Rev Limiting: Many CDI boxes, including the one in your 2008 Polaris Sportsman 90, include a rev limiter. This prevents the engine from over-revving, which can cause serious damage. The CDI box cuts off the ignition spark when the engine reaches a certain RPM, protecting it from harm.

Why CDI Boxes Fail:

CDI boxes are electronic components, and like any electronic device, they can fail over time. Here are some common reasons why your CDI box might be giving you trouble:

• Age: Over time, the components inside the CDI box can degrade due to heat, vibration, and general wear and tear. This is especially true for ATVs that are frequently used or stored in harsh conditions.
• Moisture: Water and moisture can cause corrosion and short circuits inside the CDI box. This is a common issue for ATVs that are ridden through water or stored outdoors.
• Electrical Surges: Electrical surges, such as those caused by a faulty battery or charging system, can damage the CDI box. It's important to ensure that your ATV's electrical system is properly maintained to prevent these surges.
• Vibration: Constant vibration can loosen connections and damage internal components inside the CDI box. This is especially true for ATVs that are ridden on rough terrain.

Understanding these basics will help you better diagnose and address any CDI-related issues you might encounter.

Common Symptoms of a Failing CDI Box

Okay, so how do you know if your CDI box is on its way out? Here are some telltale signs to watch out for:

• No Spark: This is the most obvious symptom. If your Sportsman 90 won't start and you've checked the spark plug, coil, and wiring, the CDI box is a likely suspect. Use a spark tester to confirm whether the spark plug is getting any spark at all.
• Intermittent Spark: Sometimes the CDI box will work intermittently, causing the engine to start and run for a while, then suddenly die. This can be due to a failing component inside the CDI box that only malfunctions when it gets hot.
• Weak Spark: A weak spark can also cause starting problems and poor engine performance. The spark might look orange or yellow instead of a strong blue color. This can be caused by a failing CDI box that isn't providing enough voltage to the ignition coil.
• Misfiring: Misfiring occurs when the engine doesn't fire on all cylinders at the correct time. This can be caused by a faulty CDI box that is sending the spark at the wrong time or not sending it at all.
• Reduced Power: If your Sportsman 90 feels sluggish and lacks its usual power, a failing CDI box could be to blame. The engine might not be running at its full potential due to improper timing or a weak spark.
• Engine Cutting Out: The engine might suddenly cut out or stall, especially at higher RPMs. This can be caused by the rev limiter in the CDI box malfunctioning or the CDI box failing to provide a consistent spark.

If you're experiencing any of these symptoms, it's time to investigate your CDI box further.

Diagnosing the CDI Box

Before you rush out and buy a new CDI box, let's do some troubleshooting to make sure it's really the problem.

Tools You'll Need:

• Multimeter: A multimeter is essential for testing the electrical circuits in your ATV. You'll use it to check for voltage, continuity, and resistance.
• Spark Tester: A spark tester is a simple tool that allows you to visually check the spark at the spark plug.
• Wiring Diagram: A wiring diagram for your 2008 Polaris Sportsman 90 will help you trace the wires and identify the correct connections.
• Basic Hand Tools: You'll need some basic hand tools like screwdrivers, pliers, and wrenches to remove and inspect the CDI box.

Step-by-Step Diagnosis:

1. Visual Inspection: Start by visually inspecting the CDI box for any signs of damage, such as cracks, melted plastic, or corrosion. Check the wiring harness and connectors for loose or damaged wires.
2. Check the Connections: Make sure all the connections to the CDI box are clean and secure. Use electrical contact cleaner to remove any dirt or corrosion from the connectors. Loose or corroded connections can cause intermittent problems.
3. Test the Spark: Use a spark tester to check the spark at the spark plug. If there's no spark or the spark is weak, the CDI box could be the problem. However, it's also possible that the problem is with the ignition coil, spark plug wire, or stator.
4. Test the Stator: The stator is responsible for generating the electricity that powers the ignition system. Use a multimeter to test the stator output according to the specifications in your ATV's service manual. A faulty stator can cause the CDI box to malfunction.
5. Test the Pickup Coil: The pickup coil sends a signal to the CDI box telling it when to fire the spark plug. Use a multimeter to test the pickup coil resistance according to the specifications in your ATV's service manual. A faulty pickup coil can cause timing problems.
6. Check the Wiring: Use a wiring diagram and a multimeter to check the wiring between the CDI box, stator, pickup coil, ignition coil, and battery. Look for any shorts, opens, or high resistance in the wiring.
7. Substitute a Known Good CDI Box: If you have access to a known good CDI box, try swapping it into your ATV. If the problem goes away, then you know the original CDI box is faulty. This is the most definitive way to diagnose a CDI box problem.

Important Note: Before testing any electrical components, disconnect the battery to prevent accidental shorts or electrical damage.

Replacing the CDI Box

If you've determined that your CDI box is indeed faulty, it's time to replace it. Here's how:

Steps for Replacement:

1. Disconnect the Battery: Always disconnect the battery before working on any electrical components. This will prevent accidental shorts and electrical damage.
2. Locate the CDI Box: The CDI box is usually located under the seat or near the engine. Refer to your ATV's service manual for the exact location.
3. Disconnect the Wiring Harness: Disconnect the wiring harness from the CDI box. Take note of the wire colors and positions so you can reconnect them correctly.
4. Remove the Old CDI Box: Remove the mounting screws or bolts that hold the CDI box in place.
5. Install the New CDI Box: Install the new CDI box in the same location as the old one. Secure it with the mounting screws or bolts.
6. Reconnect the Wiring Harness: Reconnect the wiring harness to the CDI box. Make sure all the connections are clean and secure. Double-check the wire colors and positions to ensure they are correct.
7. Reconnect the Battery: Reconnect the battery.
8. Test the ATV: Start the ATV and test it to make sure the problem is resolved. Check for proper starting, idling, and acceleration.

Choosing a Replacement CDI Box:

When choosing a replacement CDI box, you have a few options:

• OEM CDI Box: An OEM (Original Equipment Manufacturer) CDI box is the same as the one that came with your ATV. It's the most reliable option, but it's also the most expensive.
• Aftermarket CDI Box: Aftermarket CDI boxes are made by third-party manufacturers. They can be less expensive than OEM CDI boxes, but the quality can vary. Be sure to choose a reputable brand.
• Performance CDI Box: Performance CDI boxes are designed to improve the performance of your ATV. They may have features like adjustable timing curves or higher rev limits. However, they can also be more expensive and may require other modifications to your ATV.

Preventing Future CDI Box Problems

Here are some tips to help prevent future CDI box problems:

• Keep it Dry: Avoid riding your ATV through deep water or storing it in a damp environment. Moisture is a major cause of CDI box failure.
• Protect from Vibration: Use rubber mounts to isolate the CDI box from vibration. This will help prevent damage to the internal components.
• Maintain the Electrical System: Keep your ATV's electrical system in good condition. Check the battery, charging system, and wiring regularly. Repair any problems promptly.
• Use a Battery Tender: If you store your ATV for extended periods, use a battery tender to keep the battery charged. This will prevent electrical surges that can damage the CDI box.

Conclusion

Troubleshooting a CDI box can seem daunting, but with a systematic approach and the right tools, you can diagnose and fix the problem. Remember to always disconnect the battery before working on the electrical system, and take your time to ensure that all connections are clean and secure. By following these tips, you can keep your 2008 Polaris Sportsman 90 running smoothly for years to come. Good luck, and happy riding!