339-856991A1 339-850227 Ignition Coil for Mercury EFI Optimax Sport Jet | JLM Marine

Ignition Coil for Mercury EFI Optimax Sport Jet – Fits 135-250 HP 6-Cylinder Engines

This high-quality aftermarket ignition coil is engineered for Mercury EFI, Optimax, and Sport Jet outboard engines. Designed to fit 6-cylinder 2.5L and 3.0L models from 1998 to 2006, it delivers reliable spark performance for 135 HP to 250 HP applications.

This ignition coil directly replaces Mercury part numbers 339-856991A1, 339-850227, and Sierra part number 18-5187. It meets or exceeds OEM specifications for reliable engine operation.

• Direct-fit replacement for Mercury 6-cylinder EFI, Optimax, and Sport Jet engines
• Meets or exceeds OEM performance standards
• Package includes one complete ignition coil assembly

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Mercury owners, here's a guide to help you identify your engine's serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

Technical Specifications

Package Contents

• 1 x Ignition Coil

Installation Guide

1. Disconnect the negative battery cable to prevent electrical shock or short circuits.
2. Locate the ignition coil on your engine; refer to your engine's service manual or parts diagram for exact positioning.
3. Disconnect the spark plug wire from the old ignition coil. Label wires if multiple coils are present.
4. Disconnect the electrical connector from the ignition coil.
5. Remove the mounting bolts or screws securing the old ignition coil to the engine block.
6. Carefully lift the old ignition coil away from the engine.
7. Position the new ignition coil in the same location and align the mounting holes.
8. Secure the new coil with the original mounting bolts or screws; tighten to manufacturer specifications.
9. Reconnect the electrical connector firmly until it clicks into place.
10. Attach the spark plug wire to the new ignition coil, ensuring a secure connection.
11. Reconnect the negative battery cable.
12. Start the engine and verify smooth operation with no misfires or rough idling.

Troubleshooting & FAQ

Q: How do I confirm this ignition coil fits my engine?
A: Check the Compatible Engine Models table above for your engine's brand, model, HP, and year range. You can also cross-reference the OEM part numbers (339-856991A1, 339-850227) with your original coil or consult your engine's parts diagram.

Q: What are the symptoms of a failing ignition coil?
A: Common signs include engine misfires, rough idling, difficulty starting, loss of power under load, and increased fuel consumption. If your engine runs poorly on certain cylinders, the ignition coil may be faulty.

Q: How often should I replace my ignition coil?
A: Ignition coils typically last several years under normal operating conditions. Replace them when you notice performance issues or during routine maintenance if they show signs of corrosion, cracking, or electrical failure.

Q: What is the difference between this aftermarket coil and the OEM version?
A: This aftermarket ignition coil is manufactured to meet or exceed OEM specifications using comparable materials and design. It provides reliable performance at a more competitive price point compared to OEM parts.

Q: Can I install this ignition coil myself?
A: If you have basic mechanical skills and tools, installation is straightforward. However, professional installation is recommended to ensure proper fitment, electrical connections, and optimal engine performance.

Q: Is this an OEM part or aftermarket?
A: This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

Q: How fast do you ship and how much does it cost?
A: We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

Q: What is your warranty and return policy?
A: This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.