Toyota Misfire Diagnosis Without Using an Expensive Scanner

A misfiring engine is one of the most common engine problems you will experience with any internal combustion engine vehicle during at least some time during your ownership of a car beyond its warranty period or after buying a used car. When an engine is misfiring, you will often see a "Check Engine" warning light on your dashboard display.

Aside from the "Check Engine" warning light, the possibility that your engine is misfiring is easily identifiable by how the car's engine behaves compared to its normal operation.

What is a Misfiring Engine?

A misfire occurs when one or more of the engine's cylinders fail to properly complete the combustion cycle. This can cause a rough idle, a loss of power, poor fuel efficiency, and sometimes a noticeable jerk or hesitation during acceleration.

Reasons for a misfire include:

1. Ignition system problems: Faulty spark plugs, ignition coils, or spark plug wires can prevent the air-fuel mixture from igniting properly.
2. Fuel system issues: A clogged fuel injector, low fuel pressure, or a failing fuel pump can lead to an insufficient fuel supply, causing misfires.
3. Air intake problems: A dirty or clogged air filter or problems with the throttle body can disrupt the air-fuel ratio.
4. Engine mechanical issues: Low compression due to worn-out pistons, rings, valves, or even timing issues can lead to misfiring.
5. Sensor or computer malfunctions: Sensor malfunctions, such as the oxygen sensor or mass airflow sensor, can affect the fuel-air mixture, leading to misfires.

Unfortunately, too many DIY mechanics tackle the problem of a misfiring engine by firing the parts cannon at it, hoping that replacing the coils or spark plugs (or both) all at once will solve the problem without having to go to a garage for a diagnosis and repair.

However, as the reasons for a misfire listed above show, firing the parts cannon this way covers just one of the 5 possible causes, meaning that all else being equal, you have a 20% chance of being correct. Worse yet, however, is the fact that coils are expensive, and you are wasting money that could be better spent.

Related article: Common Car Maintenance Mistake Owners Make When Diagnosing Their Car's Engine Problems

A Better Way to Spend Your Money

Ideally, owning and using a top-rated scan tool like the professionals' use would be the correct way to diagnose your car's engine problem. However, the scan tools many garages depend on to speed up the time spent diagnosing and move onto the correct repair and then the next billable customer are prohibitively expensive and beyond the budget of most DIY home garage mechanics.

But there is at least one alternative that works and will not cost you an arm and a leg. In fact, it could easily pay for itself with your first successful engine misfire diagnosis and repair: A portable and easy-to-use waveform engine ignition analyzer sold on Amazon for about $270.

How To Diagnose A Misfire Without Using A Scanner

That was the message in a demonstration on the Royalty Auto Service YouTube channel where the host showed how a relatively inexpensive ignition analyzer he bought can be used to determine whether a misfiring engine is due to bad spark plugs, a bad coil, or a possible bad fuel injector.

The demonstration was performed on a 2002 Toyota Tundra with a check engine light warning and engine operation indicative of a missing cylinder problem.

Follow along with the host as he walks you through how he could easily find the problem cylinder and then narrow the cause between being either the spark plug or the coil.

Additional Resources for Diagnosing a Misfiring Engine

By following the instructions that come with the analyzer demonstrated, you should be able to come up with a reasonable diagnosis without firing the parts cannon and hoping that some random part replacement will do the trick.

However, if you are a more adventurous and an inquisitive DIY mechanic, there are other resources to consider that will not only improve your diagnostic skills but will also remove the mystery of what the waveforms on the display screen mean exactly. Furthermore, there is an even cheaper tool that is very similar to the one in the video above that will turn your laptop into a multifunctional scan tool for automotive diagnostic work―the PicoScope 2204A, priced at $165, is another type of waveform engine ignition analyzer sold on Amazon.

To learn more about how the PicoScope does the same task (and much more) as the earlier demonstrated ignition analyzer, here is a useful demonstration by a mechanic working on a misfiring engine on a 2018 Ford Fiesta.

Find Misfires Fast! How To Check Misfire PicoScope 2204A Automotive Diagnostics

For some text learning to supplement the two videos, a nearly academic resource recommendation can be found on Motor.com online magazine with an article titled "Fire in the Hole: Understanding Ignition Waveforms" that explains everything you will ever want to know about ignition waveforms to increase your understanding of what you are doing and how your ignition analyzer is showing and interpreting those waveforms. Be sure to click on the pdf link at the end of the article to see the referenced figures on a free downloaded PDF.

That all said and done, Good Luck on using this article's info to increase your automotive skill set and maybe even save some money in the process.

For additional automotive diagnosis-related articles, here are three for your consideration:

• 3 Simple Tests to Diagnose This Common Used Car Problem
• Exhaust Smoke Diagnosis Explained in Detail
• Best Car OBD2 Code Scanner and the Manual to Help You Understand How to Use It

Timothy Boyer is an automotive reporter based in Cincinnati who currently researches and works on restoring older vehicles with engine modifications for improved performance. He also reports on modern cars (including EVs) with a focus on DIY mechanics, buying and using tools, and other related topical automotive repair news. Follow Tim on Twitter at @TimBoyerWrites as well as on Facebook and his automotive blog "Zen and the Art of DIY Car Repair" for daily news and topics related to new and used cars and trucks.

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