An engine functions as a pump, requiring a precise combination of fuel, air, and spark. If any element of this trio is imbalanced, your Subaru Exiga won’t run right (or at all).
While a misfire is the symptom of bad spark plugs, bad spark plugs almost always indicate a problem with the engine (more on that in section 2).
How Spark Plugs Work
The fundamental design and function of spark plugs have remained broadly consistent over the past century. In the Subaru Exiga, they are positioned atop the combustion chamber and ignite the air-fuel mixture, initiating the engine’s power stroke.
Something that has changed about modern spark plugs is that many of them use iridium, don’t need to be gapped, and can last for 100k miles with little issue.
That being said, they still can go bad. The good news is that if you do need to replace your Exiga’s plugs, they are very affordable.
Bad Spark Plug Symptoms: Subaru Exiga
There are a lot of potential symptoms related to foul spark plugs in your Exiga. We always recommend using an OBDII scanner to pull your trouble codes if you have a check engine light on. It can really narrow your search down. If you don’t have one, your local parts store will do this for you for free.
It is also worth noting that the symptoms of bad spark plugs in your car will be almost the same as any other bad part in the ignition process. Bad coil packs will produce the same results and feel like bad plugs.
Check Engine Light
The check engine light is one of the most common symptoms of bad spark plugs. More often than not, your Exiga’s computer can detect bad spark plugs in your car.
Trouble Codes Can Aid Your Diagnosis
There are several misfire-related trouble codes.
- P0300– this trouble code indicates that there is a random misfire. A random misfire means that a misfire is detected, but the ECM is not able to determine which cylinder it is coming from, or the misfire is occurring randomly.
- P0301 through P0312- these trouble codes indicate that there is a misfire in one specific cylinder. For example, P0304 is for a misfire in cylinder 4.
Accelerates Slower than Normal
As you ask your Exiga for more power, the fuel and ignition systems respond. If acceleration has diminished, it should be felt. The fewer cylinders that your engine has, the more that one cylinder not firing correctly will have. If you have one or more bad spark plugs, it’ll cause the acceleration of the Exiga to be weaker.
Fuel Economy
The less efficient your engine’s combustion, the more fuel will be wasted. This leads to a decrease in fuel economy.
When you take your Exiga in for a tune-up due to decreased fuel economy, checking the spark plugs (and ignition system in general) is going to be one of the very first places a mechanic will look at.
Misfire
Misfiring is the most common symptom of bad spark plugs. All of the other symptoms are a result of the misfiring itself. The real question is, what is causing the misfire? There is more to your Exiga’s ignition system than just the plugs. There are also coil packs and spark plug wires.
There are also non-ignition-related circumstances that can cause your Subaru Exiga to misfire. That would include a lack of fuel pressure, bad fuel injectors, or even a timing chain (or belt) that has jumped. Since there are so many reasons that a vehicle can misfire, we recommend testing for trouble codes first.
Rough Idling
When a spark plug is misfiring, it is often most pronounced at idle speed. This is because when your car’s engine turns slower, it is easier to detect. You’ll feel a rough vibration.
Diagnosing Bad Spark Plugs
There are two parts to diagnosing bad spark plugs in your Exiga. The first is to identify the misfiring cylinder. The second is to inspect the plug. If it looks ok, follow the diagnostic steps listed below. If it doesn’t look ok, use the chart below to determine why the plug has gone bad.
Diagnose Using The Swap Test
If your Exiga has a cylinder-specific misfire code, you can swap parts to diagnose what’s failed. You will need an OBD II code scanner.
Here’s how:
- Identify the misfiring cylinder by pulling the code with an OBD II scanner. The last two numbers in the P03XX code correspond to the misfiring cylinder.
- Pull the spark plug and swap it with any other cylinder that doesn’t have a code.
- Clear the codes with a code scanner.
- Start your Exiga’s engine and wait for the code to return.
- If the code number changed to another cylinder, replace the part you pulled.
- If the code doesn’t change, keep repeating with other ignition components associated with the cylinder in question.
Inspect the Plug
The most common reason a modern vehicle’s spark plug wears out is the wearing down of the electrode (normal wear), followed by carbon deposits. Consult the chart below to help you determine why your Exiga’s spark plug went bad.
Conclusion: Bad Spark Plugs Subaru Exiga
Be aware that almost all symptoms of a bad spark plug in your Exiga could also be other issues with the ignition system. Good luck diagnosing the problem. Feel free to leave a comment below if there is anything that you would like to add.