Ignition Diagnostic Tool Comparison Table
| Tool Description | Cost | Complexity | Usefulness |
|---|---|---|---|
| fixed-gap inline spark checker | $ | 🧠🧠 | ⚡⚡ |
| adjustable gap spark tester | $ | 🧠🧠🧠 | ⚡⚡ |
| socket-style spark plug tester | $$ | 🧠 | ⚡ |
| spark kV checker | $$ | 🧠🧠 | ⚡⚡ |
| ignition scope | $$$$ | 🧠🧠🧠🧠🧠 | ⚡⚡⚡⚡ |
| engine analyzer | $$ | 🧠🧠 | ⚡⚡⚡ |
| engine ignition analyzer | $$$ | 🧠🧠 | ⚡⚡⚡⚡⚡ |
| OBDII scan tool | $$ - $$$$$ | 🧠🧠🧠 | ⚡ - ⚡⚡⚡ |
Inline Spark Checker
The ‘inline spark checker’ is basically a high-voltage spark plug wire extension cord with a light bulb in the middle of it. The bulb lights up each time that current is discharged through the wire, which shows you whether the spark plug it’s attached to is sparking.
This tool is cheap, easy to understand, and simple to use, though you must turn the engine off each time you want to check a different plug/wire. Inline checkers work best on small engines with magneto ignitions (like chainsaws and trimmers) where everything is easily accessible, and there are few common causes of problems.
The trouble with these tools comes from its simplicity. The light bulb doesn’t give you any detailed information on the spark strength, timing, or consistency.
Adjustable-Gap Spark Testers
An adjustable spark tester is simply a high-voltage spark plug wire extension cord with an adjustable spark gap in the middle of it. By adjusting the size of the gap, you can see how long of a spark the system can generate, and maybe what that spark looks like.
Adjustable gap spark testers cost about the same as inline spark checkers (sometimes a little more), and they’re also very simple to use. These tools are usually used on engines which have trouble starting or running smoothly, when the mechanic thinks the ignition coil is ‘weak’. Users generally test to see that the system produces a spark of a certain length, consistency, and sometimes color (usually a bright violet/purple). The maximum length of a spark is determined by the ignition system’s characteristics, including the charging current going into the ignition coil, as well as the transformer ratio in the ignition coil, and the strength of the dielectric in the coil’s housing.
The trouble with these tools is that they don’t give you much information, as well as being dangerous, and likely to damage the ignition system. The spark’s length only measures the maximum voltage that the system can generate, which doesn’t tell you much, as the spark could have a very high voltage, but output very little energy. This test is very dangerous, because sparks often jump in unexpected directions, and frequently shock the technician performing the test. The test is also likely to over-stress and damage the dielectric in the ignition coil.
We (at GTC) do not think these are very useful, or worth the risk of using but if you do choose to use this, we recommend that you pick one which has a translucent or transparent polycarbonate (plastic) window for your safety. The window will help to contain the poisonous ozone gas (which smells a bit like chlorine bleach), and protect your eyes from the harmful ultraviolet (light) radiation produced by the sparks.
Socket-Style Spark Plug Testers
Plug-in socket-style spark plug testers are usually little boxes with two sockets for you to (temporarily) install a couple of plugs, and see whether sparks appear between their electrodes. These testers usually apply a moderate (<3kV) voltage to one connection on each plug, and allow you to see whether a spark appears across the electrodes, and examine its consistency.
These tools cost a little more than the inline spark testers, but they’re usually sold cheap by a variety of low-cost importers. Seeing the sparks isn’t very useful in itself, and exposes your eyes to dangerous ultraviolet radiation (UV light), but it can help you spot cracks in spark plug insulation which is allowing sparks to ‘leak’ to the engine block.
The only big downside to this tool is the UV/ozone exposure, but most people only use them once or twice as a novelty, then throw them out.
Spark kV Checkers
There are a few different tools that can quickly check spark peak voltage on a running engine, some just detect large voltages and indicate relative size, while others display additional information. The Waekon 76760 is a popular example of a simple detector, and our GTC TA100 is a more advanced model, capable of displaying engine speed (RPM) as well as spark peak voltage. Both tools has a sensor/probe which is positioned near or around the high-voltage spark plug wire, and allows the tool to measure the voltage and display it on an LCD screen.
Spark kV testers can be very useful tools in the right hands, especially on two-cylinder engines, where you can easily access the spark plug wires, and you can compare your readings. Many small engine mechanics use these tools daily, and they often prefer the ones with an RPM readout, as this makes setting the idle on these engines quick and easy.
These tools well on small engines and some older large engines, but not on modern coil-on-plug systems. Additionally, spark kV checkers do not provide enough information to diagnose issues like occasional misfires.
Engine Analyzers
There are analog and digital engine analyzers, in both cases, they are boxes with an AC current pickup that is clamped around the ignition coil’s power cable. The ‘engine analyzer’ detects the ignition ‘dwell’, and displays engine speed (RPM), dwell angle (in percent or degrees depending on the instrument), and sometimes a few other details.
These tools were common from the 1960s to the 1980s when they were often used as tachometers in auto-repair shops, as well as for checking and adjusting the dwell angle settings on distributors.
Engine analyzers are no longer common, because electronic distributors (common since the 1980s) don’t have adjustable dwell, and the the AC current clamps are very hard to use with coil-on-plug systems (common since the early 2000s), if they work at all.
As an aside, engine analyzers must be one of the most ‘optimistically’-named automotive tools, as they only analyze the ignition system on the engine, and even then, only really tell you about what happens before the spark.
Ignition Scopes & Ignition Analyzers
Ignition scopes and ignition analyzers are oscilloscopes which have been adapted for use in ignition system troubleshooting. The scope/analyzer is usually a kit consisting of a display unit with various control knobs, and between four and eight pickups (for collecting data from all the spark plugs on one bank of cylinders simultaneously). These instruments became popular in the late 1950s, and continued to be common in professional garages until the 1990s; they gradually declined in popularity as electronic distributors (and later coil-on-plug systems) took over the automotive market.
Ignition scopes are best used by trained, skilled technicians who are familiar with the ‘normal’ waveforms produced by the ignition system they’re testing, and use the pattern (waveform) to quickly discover the causes of an engine’s problems. Many skilled technicians claim that a few features on the waveform (usually the spark ramp, burn line, and nose) will tell the engine’s whole story.
The problems with ignition scopes come from their compatibility issues, complexity, and cost. The biggest obstacle to using these instruments is that they require special and hard-to-get adapters to work on modern coil-on-plug (COP) ignition systems. These scopes also take a while to set up and get going, and can easily be damaged if any of their many wires gets caught on anything (as well as causing damage to the vehicle being tested). All of that being said, the biggest problem with these tools is that nobody makes them anymore, and they’ve been replace with engine ignition analyzers (which cost less and are easier to use).
Engine Ignition Analyzers
The engine ignition analyzer has most of the features of an ignition scope, and all the features of an engine analyzer, wrapped up in a small and portable package, with some (very useful) extra features thrown in. This hand-held instrument has a single sensor which the user positions near the spark plug wire or coil-on-plug module. The sensor picks up the spark pattern, and passes it on to the main instrument, which uses digital signal processing to extract information about the signal. The instrument can then either display the waveform (pattern), or various charts and digital readouts of the data they collect.
Engine ignition analyzers are very powerful and easy-to-use, because they help the user acquire the data, automatically adjusting themselves based on what they ‘see’. The best part of these tools is that they can display the information in a variety of ways, including the digital view if you just need to verify a tachometer reading, a chart if you’re trying to pin-down a misfire spark pattern, or the waveform graph if you’re looking for a specific feature (indicative of a problem you’re familiar with). We may be a little biased, but we think our GTC505 Engine Ignition Analyzer is the absolute best tool for testing ignition systems, and diagnosing any issues that are detected.
The downsides to this tool are, as you might have guessed, a mirror image of the features. The engine ignition analyzer only measures one cylinder at a time, and cannot be used while road-testing a vehicle, because the sensor must be manually positioned near the spark plug wire or module.. Additionally, some mechanics find the many options confusing, as they just want a tool that tells them whether something is good or bad, instead of a lot of data.
OBDII Scan Tools
On-Board-Diagnostics (OBD) scan tools (also known as ‘scanners’) have been the most popular electronic tools for diagnosing engine faults since at least 2010, and they’re available at many different price-points. These tools exist to read fault codes from Engine Control Modules (ECM) and Engine Control Units (ECU) aboard most modern (post-1995) passenger vehicles and some commercial vehicles. Fault codes will often provide clues as to what part of an engine is having trouble, but scan tools do not provide enough information required to find the cause of an ignition fault. Scan tools are also incompatible with most gasoline engines, as OBD-equipped vehicles make up a small portion of all engines (, think of all the lawnmowers, chainsaws, generators, boats, and ATVs).
We definitely recommend that all mechanics working on modern road vehicles have access to at least one scan-tool, just don’t expect it to ‘tell’ you what part of the ignition system is causing you trouble.
Which Should You Get?
It depends!
Whether you should get an ignition testing tool and which one you should get is a tough question to answer here, as it really depends on what kind of engines you work on, and what you’re doing to them. In general, tools like these are most valuable to people who are evaluating engines with problems, restoring engines, or fixing the most expensive and complicated engines.
When you’re evaluating an engine that you’re unfamiliar with, there are many potential causes for each symptom you observe, a situation known as ‘high causal density’. Being able to narrow-down the likely causes of engine issues can help you understand whether that rough idle can be fixed quickly and easily, or is a sign that you are looking at a chunk of steel worth no more than scrap value.
Engine restoration is another ‘mine-field’, as old and used components are hard-to-get, and often expensive, so you can’t just ‘replace and pray’ (which is what many dealerships do these days). If this is what you do, having to find and buy parts that don’t help you, but do slow down the project is a huge problem, which means that precise diagnosis is time (and money) well-spent.
If you work on complicated or expensive engines, diagnostic tools often pay for themselves in at least one of three different ways. First, the replacement parts for these engines are often expensive, so buying a bunch of them and using the ‘guess and check method’ is usually a costly strategy. Second, replacing parts on these engines is usually time-consuming, as everything is tightly-packed, so each removal and re-installation (re-and-re) wastes the one thing you can’t buy more of: time. Lastly, expensive engines are usually important, and time out-of-service is costly and inconvenient to the system’s user, so getting the engine running again is important (and valuable).
In any of these three cases, we’d recommend getting an engine ignition analyzer, ignition scope, or engine analyzer. Which one is best for you depends on the vintage of engine you’re working on, and which tool you’re most comfortable with.
That's All!
If you work on spark-ignition systems, we hope you’ll consider our GTC505 Engine Ignition Analyzer or TA100 SmarTach+. The GTC505 and TA100 are designed and manufactured in Canada, to help you get the job done.
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