Sierra Spark Tester for 4 Cylinder Mercury Outboards, Part 18-99547

The Sierra Spark Tester, part number 18-99547, is an in-line spark checker built for diagnosing ignition problems on 4 cylinder Mercury outboard engines. Instead of pulling a spark plug and guessing at spark quality by eye, this tester lets you check for consistent, visible spark directly in line with the plug wire while the engine is cranking or running, which makes it much easier to isolate a weak coil, bad plug wire, or faulty ignition component before you start swapping parts. It is built with a copper core for reliable conductivity during repeated testing.

This is a diagnostic tool sized specifically for 4 cylinder outboard applications, so it is set up to test spark across all four cylinders of a compatible Mercury outboard engine. It is a straightforward addition to any marine mechanic's or DIY boater's toolbox for troubleshooting no-start conditions, rough idle, or misfire complaints tied to the ignition system.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-99547
• Product Name: Spark Tester - 4 Cyl.
• Category: Mercury Outboard Specialty Tools
• Cylinder Configuration: 4 Cylinder
• Core Material: Copper
• Weight: 0.8 pounds
• UPC: 808282395247

Fitment

• 4 cylinder Mercury outboard engines

Frequently Asked Questions

What does the Sierra 18-99547 spark tester do? It checks for spark on 4 cylinder Mercury outboard engines by connecting in line with the spark plug wire, letting you visually confirm consistent spark while the engine cranks or runs instead of pulling the plug to guess.

How many cylinders does this spark tester cover? The 18-99547 tester is built for 4 cylinder outboard engines, matching the ignition layout of a 4 cylinder Mercury outboard.

Is the Sierra 18-99547 only for Mercury outboards? It is categorized and sized for 4 cylinder Mercury outboard engines, so that is its intended application.

What is the spark tester's contact core made of? The core of part 18-99547 is copper, chosen for reliable electrical conductivity during repeated spark checks.

How much does the Sierra 18-99547 spark tester weigh? It weighs 0.8 pounds.

Can this tool diagnose a no-start condition? Yes, checking for spark with the 18-99547 is a standard first step in diagnosing a no-start or misfire, since it isolates whether the ignition system is delivering spark to the cylinder.

Do I need to remove the spark plug to use this tester? No, the 18-99547 connects in line with the plug wire so you can check spark without pulling the spark plug.

Is the Sierra 18-99547 a genuine Sierra part? Yes, 18-99547 is the Sierra manufacturer part number for this spark tester.

What ignition problems can this tester help identify? Weak or missing spark, a failing ignition coil, or a bad plug wire on a 4 cylinder Mercury outboard can all be narrowed down using the 18-99547 spark tester.

What is included with part 18-99547? The product is the Sierra spark tester itself, part number 18-99547, sized for 4 cylinder outboard ignition testing.