Sierra Spark Tester 18-99540 with Adjustable Open Spark Gap for 1-8 Cylinder Marine Engines

The Sierra 18-99540 Spark Tester is a diagnostic tool used to check spark output and ignition performance on marine engines with 1 to 8 cylinders. It features an adjustable section that lets you set an open spark gap, allowing you to visually confirm a strong, consistent spark rather than relying on a plug that may mask a weak or intermittent ignition signal. This makes it a practical first step when troubleshooting no-start conditions, rough running, or suspected ignition component failures on inboard and sterndrive engines.

The tester connects in place of a spark plug in the ignition circuit, giving technicians and boat owners a quick visual reference for spark quality across each cylinder. It is compatible with engines ranging from single-cylinder to 8-cylinder configurations, making it a versatile tool for a wide range of marine powerplants. Replacement spark plug wire tips and metric adapters are available separately for use with this tester, extending its compatibility with different wire terminal styles.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-99540
• Product Name: Spark Tester with Adjustable Section
• Cylinder Compatibility: 1-8 cylinder engines
• Spark Gap: Adjustable, open spark gap
• Weight: 1.3 pounds
• Product Dimensions: 4.02 x 12.01 x 7.99 inches
• Package Quantity: 1
• UPC: 736983855831
• OEM Cross-Reference: CDI Electronics 519S48

Fitment

• 1-8 cylinder marine engines

Replaces (OEM)

• CDI Electronics 519S48

Frequently Asked Questions

What is the Sierra 18-99540 spark tester used for? It checks spark output and ignition quality on marine engines with 1 to 8 cylinders by letting you view an open spark gap in place of a spark plug, which helps confirm whether the ignition system is firing correctly.

How many cylinders does this spark tester support? The Sierra 18-99540 is rated for engines with 1 to 8 cylinders, covering everything from single-cylinder outboards to V-8 inboard and sterndrive engines.

Is the spark gap adjustable? Yes, the 18-99540 has an adjustable section that lets you set the open spark gap, so you can vary the test conditions and better judge spark strength and consistency.

Does the Sierra 18-99540 have an equivalent OEM part number? Yes, the Sierra 18-99540 corresponds to CDI Electronics part number 519S48, so either number will identify the same spark tester.

How much does the 18-99540 spark tester weigh? It weighs 1.3 pounds.

What are the dimensions of this spark tester? The Sierra 18-99540 spark tester measures 4.02 x 12.01 x 7.99 inches.

Can I replace the spark plug wire tips on this tester? Yes, replacement spark plug wire tips (P/N 519-48TA) are available separately for use with the 18-99540 spark tester when the original tips wear out.

Are metric adapters available for this tool? Yes, metric adapters (P/N 519-48M) are available separately for the 18-99540 spark tester for use with metric-threaded plug wires.

How many spark testers come in the package? The Sierra 18-99540 spark tester ships as a package quantity of one unit.

What is the UPC for the Sierra 18-99540 spark tester? The UPC for this spark tester is 736983855831.

Is this spark tester suitable for troubleshooting a no-start condition? Yes, checking spark output with the 18-99540 is a common first diagnostic step for no-start or rough-running conditions, since it lets you see whether each cylinder is producing a strong spark.