How to Examination a Spark Plug to Run into If It's Working

Every small gasoline engine has a spark plug, and this fundamental component requires periodic inspection and testing. Learn how to exercise it here.

Time

An hour or less

Complexity

Beginner

Toll

Free

Introduction

Spark plugs are plant in all gasoline engines. Their job is to ignite the air/fuel mixture within the engine with just the right timing. Historic period, use and poor fuel quality tin all contribute to a spark plug that's muddy and doesn't spark properly.

Failure to showtime or hard starting are two symptoms of a bad spark plug, as is crude running, college fuel consumption and less ability than usual. Learning to test a spark plug is a basic office of troubleshooting any small engine. The task takes just a few minutes and costs petty or zero.

How spark plugs work

  • Spark plugs are always located at the top of the cylinder caput of small engines. Cylinders like these accept cooling fins on the exterior and are one of the largest parts of whatever small gasoline-powered engine.
  • All spark plugs thread into a hole in the cylinder head.
  • A thick wire and plumbing equipment pushed over the stop of the spark plug delivers the electrical power needed to make the subconscious tip of the spark plug spark.
  • The ignition system of the engine sends a pulse of very-loftier-voltage current through this wire and into the spark plug — typically 20,000 to 30,000 volts for a pocket-sized engine.
  • The tip of the plug sits simply inside the combustion bedchamber of the engine in the cylinder head and includes a small gap.
  • When high-voltage electricity encounters this gap, it jumps the air space on its fashion to complete the circuit by flowing into the engine block. This jumping creates a visible spark that ignites the air/fuel mixture inside the engine and so information technology can run.
  • All problems with spark plugs boil down to a handful of deficiencies that foreclose or impair electricity from jumping the all-important spark plug gap.

Tools Required

Project stride-by-stride (4)

Step ane

Remove the spark plug wire

  • Remove the shroud that covers the spark plug on a chainsaw or outboard motor. Small engines on lawn mowers and backyard tractors commonly do not have spark plug shrouds.
  • Pull the ignition wire off the finish of the spark plug. Don't just yank on the torso of the wire itself, though, considering this tin cause damage. Reach down effectually the sides of the spark plug and gently pull on the terminate fitting of the wire that sits over the top of the spark plug.
  • If the cap and ignition wire don't want to come up off, rotate the rubber plumbing equipment i fashion or the other equally you pull.

Removing Spark Plug Wire

Step ii

Examination with a spark plug tester

  • Attach a spark plug tester to the ignition wire. At the other end, the tester connects to the spark plug equally it sits in your engine.
  • Turn the ignition ON.
  • Offset the engine, or but turn it over if it won't showtime, and watch the transparent sides of the tester. If no visible spark or glow is nowadays, so you can be sure that no spark is occurring at the earth-shaking tip of the spark plug. Does this mean the plug is bad? Non necessarily. The spark plug could be bad, yes, simply lack of spark can also be caused by a fault somewhere else in the ignition organisation.

Spark Plug Tester Glowing

Step three

Or, test without a spark plug tester

  • Apply a suitable spark plug wrench to loosen and remove the plug from the engine by rotating it counterclockwise. Of form, this has to happen with the ignition wire removed.
  • Reconnect the ignition wire onto the top of the loose spark plug, then position the plug and then the lower metal body is touching a metal part of the engine cylinder caput.
  • Turn the engine over and watch the gap at the tip. Note that the engine can't run with the spark plug removed like this, but it volition turn over freely. If the spark plug and the remainder of the ignition arrangement are working properly, you should meet an obvious blue spark arcing betwixt the tip of the inner primal electrode of the plug and the curved metal summit that arcs downwardly near it equally the engine turns over.
  • Bank check to make sure the ignition is ON if there is no visible spark, then try again. If the spark remains absent or weak, y'all're on track to sorting out the crusade of your engine trouble.

Spark Testing

Step 4

Assess your findings

  • Look at the tip of the removed spark plug. A spark plug should come out of an engine with a cardinal electrode that's got a light grayness or dark-brown balance. It should be complimentary from whatsoever oily or fluffy black deposits that could permit loftier-voltage electricity to bypass the gap and fail to spark, preventing your engine from starting or running properly.
  • Supercede the spark plug with a new one of the aforementioned kind (a standard spark plug costs $5 to $eight). If the new plug fails to make your engine start and run well, the trouble is with some other part of the ignition or fuel system. You lot've proven that the spark plug is non the cause of the trouble and your testing is complete.

Spark Plug Tip

Originally Published: February 11, 2021