Can spark plugs cause misfire only under load?

[MerlintheMad]

Hi, all.

I've assumed that when spark plugs are faulty, they misfire all the time. But is it possible that they only misfire when you push for heavy acceleration?

I'm soon to take my car in for a service. The last one in early October I had my plugs changed (recommended) at c. 45K miles. Since that spark plugs swap, I've noticed what I have referred to as "chugging", or hesitation, stutter, as I demand heavy acceleration (usually not WOT, though). Today, in automatic (not manual gate), and Sport mode, two times I got on it pretty good and both times I felt the slight roughness of what I think could be misfiring, which evens out after a couple of seconds, maybe less. Anyway, as the title asks: is it normal for spark plugs to work smoothly at all other times except when demanding a lot of acceleration? I plan to bring this up at the service in a couple of weeks and would like to know more than I do right now. Thanks.

 

[JSolo]

I would imagine spark plugs misfire under load when there's a coil problem or improper gap. My understanding (and I could be completely wrong), under load more is demanded of the coils because they have to generate power quicker (higher rpm) per unit time. So if the coil are worn out this could present an issue.

If plugs have excessive gap, even more is demanded of the coils under load.

Did you replace the plugs with the same part # as what came out? Were these plugged sourced on amazon, ebay or similar? Or did they come from the dealer. Lots of fakes (inc spark plugs) out there.

It's also possible there's a bad connection between one or more coils and the plug.

 

[MerlintheMad]

Plugs are OEM from the dealer. Thanks for the sleuthing.

 

[JSolo]

If the only thing changed was the plugs then something plug related is causing this The coils definitely get manipulated in plug replacement (Coil on plug ignition), so possible something's up with a coil. Aside from that, bad gas¿?

 

[DoctorStiches]

Could be a weak spark to begin with or a bad gap and then the pressure that the Turbo puts into the equation blows out the flame causing a misfire

 

[MerlintheMad]

bad gas¿?

Lol. No. Costco exclusively until once last week when I went to Holiday/Sinclair because Costco Gas was a total zoo. So, three months of bad gas?

Could be a weak spark to begin with or a bad gap and then the pressure that the Turbo puts into the equation blows out the flame causing a misfire

This is what I am trying to find out. You are helping a lot, if I can basically quote what you say here to the techies in a week or two. Misfire under boost, or significant boost, must be related somehow to the spark plug replacement job that they did in early October. Maybe all I have is one defective plug?

 

[DoctorStiches]

De

Lol. No. Costco exclusively until once last week when I went to Holiday/Sinclair because Costco Gas was a total zoo. So, three months of bad gas?

This is what I am trying to find out. You are helping a lot, if I can basically quote what you say here to the techies in a week or two. Misfire under boost, or significant boost, must be related somehow to the spark plug replacement job that they did in early October. Maybe all I have is one defective plug?

Defective plug or coil or intermentent connection loss from corrosion.... im picking at strings but my only random misfire problems were back in 2018 and i upgraded to hks plugs woth no hiccups since

 

[DoctorStiches]

Gotta add that gas is seasonal and maybe your tank got some summer fuel and it runs worse in low temps? Just a guees again

 

[MerlintheMad]

She ran pretty well today. But although I used the paddles and held the RPMs to between 3 and 4K before shifting, I was hesitant to actually push past c. halfway on the accelerator; so, I don't know. Just gassed up at Costco and will try some kickdown switch accelerations tomorrow.

 

[DoctorStiches]

She ran pretty well today. But although I used the paddles and held the RPMs to between 3 and 4K before shifting, I was hesitant to actually push past c. halfway on the accelerator; so, I don't know. Just gassed up at Costco and will try some kickdown switch accelerations tomorrow.

Plrase dont hate me but when i stopped using costco fuel i stopped haveinf missfire. I also changed plugs so its usless data

 

[MerlintheMad]

Got in a few good freeway accelerations today.

The first was on a cloverleaf two lanes wide, I swung to the outside lane and moved on a sedan following an F-150; the truck driver increased cornering speed to keep me from passing, but as we neared the top I pushed to the kickdown switch. I was in Custom, which has the engine set to Eco (but WOT is WOT in all drive modes), and I was in manual gate and rounding the cloverleaf in 4th gear: I knew from past experience that I had just turned over the shifting below 4th gear to the ECU, and engaging the kickdown switch downshifted to 3rd, maybe even 2nd, then as I passed the truck the trans upshifted and I was moving away in 4th gear and manually upshifted as I went: no hesitation at all: it was all smooth as silk.

The second acceleration was an onramp in Sport mode and automatic: I let the car do all the shifting, and I felt a little stutter but it was so slight that I might have imagined it, or the surface of the road was just irregular enough to cause some power cut from traction/stability control: it felt different from the "chugging" that I've described before, where it only manifests in the first second or so of acceleration: this time it wasn't nearly as noticeable and it was more or less continuous until I backed off to merge with traffic: which makes me suspect the TC/SC may have been in play.

The third time I pushed hard I was watching traffic come up on my left and, being distracted, I can't say that I felt any power loss or unevenness in the acceleration.

So, all together, it was a satisfying drive this afternoon. I'm still going to mention to the techs that I want them to check the plugs to assure that nothing visibly wrong is happening since they changed them recently.

 

[DoctorStiches]

As long as none are burnt ceramic your all good

 

[MerlintheMad]

Cracked plug.

 

[stinger123]

This sounds the same as my car. It took 4 trips to Kia and I couldn't use my car for most of September 2021. Hesitation while accelerating, intermittent check engine light, particularly during acceleration. They kept changing out a spark plug or two at a time and it kept having issues until they eventually changed all plugs. This solved things for a few months. At the time my car had only 25k on it and is completely stock.
Lucky me. It started happening again this morning, so back to Kia at 32k on my car. I am very frustrated and they won't offer me a loaner.

 

[cncBilly]

Got in a few good freeway accelerations today.

The first was on a cloverleaf two lanes wide, I swung to the outside lane and moved on a sedan following an F-150; the truck driver increased cornering speed to keep me from passing, but as we neared the top I pushed to the kickdown switch. I was in Custom, which has the engine set to Eco (but WOT is WOT in all drive modes), and I was in manual gate and rounding the cloverleaf in 4th gear: I knew from past experience that I had just turned over the shifting below 4th gear to the ECU, and engaging the kickdown switch downshifted to 3rd, maybe even 2nd, then as I passed the truck the trans upshifted and I was moving away in 4th gear and manually upshifted as I went: no hesitation at all: it was all smooth as silk.

The second acceleration was an onramp in Sport mode and automatic: I let the car do all the shifting, and I felt a little stutter but it was so slight that I might have imagined it, or the surface of the road was just irregular enough to cause some power cut from traction/stability control: it felt different from the "chugging" that I've described before, where it only manifests in the first second or so of acceleration: this time it wasn't nearly as noticeable and it was more or less continuous until I backed off to merge with traffic: which makes me suspect the TC/SC may have been in play.

The third time I pushed hard I was watching traffic come up on my left and, being distracted, I can't say that I felt any power loss or unevenness in the acceleration.

So, all together, it was a satisfying drive this afternoon. I'm still going to mention to the techs that I want them to check the plugs to assure that nothing visibly wrong is happening since they changed them recently.

Sounds like you picked up some bad gas. Be sure to ask the tech what they gap the plugs to or if they just toss them in and don’t gap.

Edit: Ahh didn’t see the cracked plug.

 

[Devin]

Sounds like you picked up some bad gas. Be sure to ask the tech what they gap the plugs to or if they just toss them in and don’t gap.

Edit: Ahh didn’t see the cracked plug.

I'm pretty sure it was the cracked plug

 

[cncBilly]

This sounds the same as my car. It took 4 trips to Kia and I couldn't use my car for most of September 2021. Hesitation while accelerating, intermittent check engine light, particularly during acceleration. They kept changing out a spark plug or two at a time and it kept having issues until they eventually changed all plugs. This solved things for a few months. At the time my car had only 25k on it and is completely stock.
Lucky me. It started happening again this morning, so back to Kia at 32k on my car. I am very frustrated and they won't offer me a loaner.

Time to start doing your own plugs!

 

[JSolo]

The instructions (I think in the service manual) say not to gap. I suppose some truth as its possible to damage the tips, but makes no sense not to verify proper gap.

 

[Devin]

The instructions (I think in the service manual) say not to gap. I suppose some truth as its possible to damage the tips, but makes no sense not to verify proper gap.

Sliding a feeler gauge into the plug certainly wouldn't hurt anything.

 

[subzero05]

most likely a coil rather than the plug