Misfire Under Load
 

Hello,

I have a 2013 FR-S and I recently changed my spark plugs 100ish miles ago. Everything seemed to be fine, I drove the car hard, cruised, etc. and had no misfires. Yesterday, however, when my tuner asked me to data log (3rd gear, 2.5k - redline pull), I heard an odd misfire noise so I decided to monitor all 4 cylinder misfires. I was able to conclude that cylinder 3 is the only cylinder to misfire and only misfires under high load (i.e. WOT 3rd gear, 2.5k - redline).

I have yet to see a check engine light despite cylinder 3 misfiring for a whole 2.12 seconds in one data log and on many other occasions. I plan on taking a look at my plug and coil pack for cylinder 3 sometime this week.

In the meantime, has anybody experienced this issue before / know how to resolve it?

Any help is appreciated, thank you!

Not enough experience on my end, as I've never had issues with this. But could it be a gap problem? Thought that should cause problems across the whole RPM range I would think. I assume they were all torqued correctly and equally. It would seem that it isn't the plugs that are they issue, but possibly the coil pack for cylinder 3.

I believe it’s the coil pack. I just ordered a new one so I’ll reply to this if it resolves the issue. I checked the gap prior to putting them in so that shouldn’t be the issue. Could having plugs that are torqued too much cause this issue? Because I eyeballed it when I did it.

Possible, but again, this should lead to potential problems or misfires throughout the RPM range, not just at peak I would think. Though I don't know that I've ever heard of a coil pack failing to produce energy fast enough right at peak RPM, it is certainly possible that it is beginning to fail. How old were your plugs when you replaced them? Did they look to be pretty worn?

They were 8+ years old with 45,000 miles on them. I attached an image of them. As far as my cylinder 3 misfire goes, is it fine to drive the car until my coil pack gets here / issue is resolved? What are the negatives of misfires to the engine long term?

Sounds like a coilpack to me. If you want to confirm, clear codes, move pack to different cylinder, run again. See if it follows the pack.

Yeah I’m going to try that out this week. The odd part is though that I have yet to receive a CEL. I’m sure at this point, I’ve had over 70+ misfires in cylinder 3.

Thanks for the help, I will keep you all posted!

I'm cheap, so I'd replace the spark plug on #3 as a test. Sure, you just replaced them all, but I've installed one that was damaged out of the package. It looked fine, but didn't run fine. Then, yeah, seems like coil pack.

As another data point - misfiring under load is a classic coil breakdown symptom. Sometimes a new plug will cover it up for a bit, but as soon as the plug picks up a little soot, or the sharp edges begin to wear off the electrodes it's back.

Yeah, I would agree it sounds like the coil pack. Worn spark plugs can certainly assist in leading to a damaged coil pack, so the one in cylinder 3 may have even been a culprit. Either way, lets see what happens once the new one goes in.

You probably won't experience any issues as long as the misfires are quite rare. Long term affect would be a shorter life span for the catalytic converter likely. But again, with how little you seem to be misfiring, there shouldn't be any big issue. Just don't go ripping on the car.

So I installed the new coil pack today, and I am misfiring a LOT less than before, but I still misfire once every blue moon only in cylinder 3. I will probably change the spark plug and check the gap before installing it. I only misfire low - mid-range RPM when the motor is under high load (usually WOT at that RPM range).

Interesting, yes at this point I would do what was said above and change the spark plug as well or check the gap at the minimum. If this plug has any defects, the last thing you'd want is to beat up your new coil pack.

Yep, I'll let you know when I change the plug if the issue is resolved. Thanks for the help!

Issue resolved! It was the spark plug. Plug gap was also 0.29 instead of factory 0.32. The car runs smoothly now! Thanks for all your help guys.