Misfires during cold start - normal?

[honman]

I just bought my first Type R - a certified preowned 2024. It's less than a year old and had just over 3k miles on it. As I keep getting used to the car, I've begun to notice some misfires during cold starts. I first noticed this happening when I was specifically paying attention to how the engine sounded when it was starting, and I immediately heard about 3-4 misfires within the ~10-ish seconds after it started. After noticing this again the next 2 times I cold started the car, I hooked up iHDS to see what was going on. It reported on average 4-6 total misfires during each cold start with the highest being 8. I don't remember which cylinders were misfiring during these tests though.

The misfires only happen while the engine is cold. During my testing, if I got misfires while starting the car, they always occurred within the first 20 seconds or so (usually sooner) after starting. Once the engine was warm, no further misfires occurred, even while restarting the engine and doing some spirited driving. I've never felt any power loss or other performance issues either. Additionally, no codes were thrown, not even on-board snapshots or hidden codes that I would only be able to see with iHDS.

So - is this typical behavior for this engine? I know cold start misfires can be common with direct-injection engines and that leads me to believe this isn't something I should be concerned about (especially since it's not throwing codes or noticeable affecting engine performance), but my paranoia wants to confirm that this is indeed the case.

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[J_D]

Is it stock and is it throwing a check engine light

 

[honman]

Is it stock and is it throwing a check engine light

100% stock, never got a CEL or code

 

[J_D]

Don't stress then. The car has a loud exhaust versus normal Hondas on cold start. My FK8 was quieter but still on the louder side and would vibrate and reflect off everything in the winter.

There are different kinds of misfires and counters the ECU records. Some reset on engine start IIRC. If it's anything that's out of the normal design range it will throw a check engine light immediately.

At least that is this internet stranger's opinion.

 

[fordsucks]

Following on the cold engine,

Just had our first few cold mornings where I'm at and not trying to kick this nest but if I start my car and get it moving in the cold without giving it a healthy chunk of time to warm up it feels uncomfortably anemic

 

[J_D]

Probably a combination of a bad fuel atomization at low temperature plus the lightweight flywheel being easy to bog down.

 

[honman]

Don't stress then. The car has a loud exhaust versus normal Hondas on cold start. My FK8 was quieter but still on the louder side and would vibrate and reflect off everything in the winter.

There are different kinds of misfires and counters the ECU records. Some reset on engine start IIRC. If it's anything that's out of the normal design range it will throw a check engine light immediately.

At least that is this internet stranger's opinion.

OK, good to know, thanks. I remember iHDS had separate counters for 2 different types of misfires but it didn't say what each "type" was. But yeah, since no CEL or codes I guess that's all within design range.

Following on the cold engine,

Just had our first few cold mornings where I'm at and not trying to kick this nest but if I start my car and get it moving in the cold without giving it a healthy chunk of time to warm up it feels uncomfortably anemic

How cold is "cold"? The coldest I've driven mine in was 45F and never noticed a drop in performance. That said, I do drive it pretty lightly until the engine temp gauge has at least 1 bar on it, unless it was warming up idling for a few minutes beforehand. My misfire issue doesn't seem to depend on ambient temp as much as engine temp - it's happened a few times starting the car cold in the 60s too.

 

[Integra23]

This is pre-owned.. I wonder if it could be running a custom tune.
On a early ethanol tune I had this issue.. @Jester04 fixed it.

 

[honman]

That thought did run through my head, but I doubt there's a tune on it. I bought it from a reputable dealer, and I really want to believe Honda wouldn't have tacked on the certified warranty if the ECU indicated it still had a tune flashed to it. I would re-flash it to stock with Honda's ECU reprogramming software just to rule out the possibility, but I believe it'll only allow the flash if the version you're flashing is newer than the one in the ECU.

 

[Jester04]

That thought did run through my head, but I doubt there's a tune on it. I bought it from a reputable dealer, and I really want to believe Honda wouldn't have tacked on the certified warranty if the ECU indicated it still had a tune flashed to it. I would re-flash it to stock with Honda's ECU reprogramming software just to rule out the possibility, but I believe it'll only allow the flash if the version you're flashing is newer than the one in the ECU.

With stock injectors it is rare to see. On cold start some idle a little funky. On bigger injectors you do need to make adjustments to make them run smooth.

 

[fordsucks]

How cold is "cold"? The coldest I've driven mine in was 45F and never noticed a drop in performance. That said, I do drive it pretty lightly until the engine temp gauge has at least 1 bar on it, unless it was warming up idling for a few minutes beforehand. My misfire issue doesn't seem to depend on ambient temp as much as engine temp - it's happened a few times starting the car cold in the 60s too.

30-40 the past few mornings

once engine warm its fine all good, but I've always been a wait for the idle needle to fall and get going but if I don't let it warm up for at least 5min she feels iffy until temps start to come up

 

[Integra23]

That thought did run through my head, but I doubt there's a tune on it. I bought it from a reputable dealer, and I really want to believe Honda wouldn't have tacked on the certified warranty if the ECU indicated it still had a tune flashed to it. I would re-flash it to stock with Honda's ECU reprogramming software just to rule out the possibility, but I believe it'll only allow the flash if the version you're flashing is newer than the one in the ECU.

Get a hondata flashpro and connect to see if the ECU has been unlocked. Dealer won't know if it's tuned.

 

[honman]

30-40 the past few mornings

once engine warm its fine all good, but I've always been a wait for the idle needle to fall and get going but if I don't let it warm up for at least 5min she feels iffy until temps start to come up

It's gotten down to the low 30s here and I'm noticing this as well. I'm pretty sure it's just because the engine needs some time to build up oil pressure and reach its ideal temperature. This is especially important for our engines because they're turbocharged. My 2017 EX-T and 2023 Touring, which both had 1.5L turbo engines, also had a noticeable drop in power before they warmed up.

 

[honman]

So it's been dropping below 20 degrees here (sometimes in the single digits) and around that time I also started getting occasional burning smells on 20+ minute drives. Ended up finding a small leak in the valve cover gasket right over the exhaust manifold. I had the dealer replace the gasket under warranty. No more leak & no more burning smell... well, other than the wonderful smell of the awful road salt they use here burning off the bottom of the exhaust pipe but not much I can do about that. Interestingly I haven't noticed any misfires since then either, even on cold starts in single digit temps.

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