Misfires in cars are quite usual and are probably in the top three for loading and firing the parts cannon. Many will replace the spark plugs, followed by the ignition coils. After that, the problem may still be there, but what to replace now?
Obviously, a misfire can be caused by bad spark plugs, of indeed bad coils. But there’s also the wiring, the engine ground, the ECM, the air intake, a fuel injector, and the engine itself that can cause misfires. And, I probably repeat myself by now: buying cheap replacements for plugs and coils might introduce a new problem in the ignition system. When you trust the part cannon to solve your problem, you gotta be prepared to eventually swap the engine!
Do not load and fire the parts cannon!
So what doi we do instead? you may ask. Simple, prior to ordering new parts, we apply logic and use our brain!
Usually, the ECM will throw a DTC for the missfire. It may even have a missfire counter that keeps track of how often the missfire occurs. The ECM will most likely tell you what cylinder does most of your misfiring. Let’s assume the DTC’s let you know that cylinder 1 is misfiring. You check the number of misfires and note a significant difference between cylinder 1 and the other cylinders. This is great, because now we can assume the other cylinders are doing great, while number 1 is in distress.
We remove the coil from cylinder 1 and another cylinder that we have easy access to. In a four-cylinder, this is likely number 2, but which one you chose doesn’t really matter. You remove the coil from that good cylinder and swap out the coils. So the perhaps bad one goes in cylinder 2, while the assumed okay one goes into cylinder 1. Now you start the engine again while keeping a keen eye on the misfire counter as well as the DTC for misfires.
If the misfire moves along to cylinder 2, then indeed the coil is likely to be the culprit. But if the error stays on cylinder 1, the coil swap didn’t fix the problem, and the issue is still with cylinder 1.
Paul
2025-12
Sweden
This page is part of a series. You can find the main page for the series here.
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