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Discussion Starter · #1 ·
I replaced my spark plugs about a year ago at 75,000 miles. Since then I have had sporadic engine issues. Every now and then the engine will miss once or twice. When it does this it goes into limp mode and won't rev over 3000rpm. Sometimes it will just go into limp mode without missing. If I pull over and shut the engine off, the issue goes away when I restart it.

I finally got annoyed enough with it to try to fix it. When I replaced the spark plugs the first time, I used AC Delco 41-800 spark plugs because that's what Advanced Auto had in stock. This time I got Denso FK16HQR11 which is what I saw recommended on this forum. I pulled one of the AC Delco plugs out and compared it to the Denso one and noticed that the Denso one is about a quarter of an inch longer on the thread section. Did I get the wrong plugs? If so, which ones are the factory plugs?

Also, could something besides the plugs have been causing the issues I was seeing? I tried cleaning my air filter, but it didn't help. (it was about 40% plugged after 60k miles of use)

Car is a 2010 Koup SX, only mod is a K&N filter

Thanks in advance.
 

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"I pulled one of the AC Delco plugs out and compared it to the Denso one and noticed that the Denso one is about a quarter of an inch longer on the thread section."

Since the Densos are recommended replacements I would suspect the Delcos for causing the sporadic missing. If they are that much shorter that means they do not extend into the compression chamber adequately.

Did you have your OBDII codes read? You should have been able to identify which cylinder or cylinders was/were causing the problem because the codes would have been set for it to go into limp mode.

BTW...next time you change something verify the new parts are the EXACT same size/shape as the parts you pull off the engine. I would have stopped as soon as I saw the plugs were not as long as the originals!
 

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Discussion Starter · #4 ·
I replaced the spark plugs yesterday with the Densos. I haven't had any issues with missing but time will tell.


Before yesterday I wasn't getting any check engine codes even after getting a miss and going into limp mode. After replacing the spark plugs I'm now getting a code for my MAP sensor. Not sure how the spark plugs would have affected that??
 

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2010 Kia Forte Koup SX 2.4L 6MT Theta 2, Titanium silver metallic.
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82569


Your local Autozone, O'Reilly's, Advanced auto parts, Pepboys, Napa will have the specific ones needed.

Always check the gaps. Doesn't matter if some armchair/keyboard warrior states "never check gaps on iridium, you don't have to check them, non iridium are only checked."

Check the gaps on each plug. Just take one to start problems & becomes a witch hunt with extreme prejudice to find the cause.

From the online manual I bought the gap is
82570


I have mine set to 45.

Hope this helps.

Anthony
 

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2010 Kia Forte Koup SX 2.4L 6MT Theta 2, Titanium silver metallic.
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Iridium spark plugs from a 07 Toyota Scion TC 2.4L auto. The guy we bought it from didn't know why the car was rough start & driving, rpms constantly surging & fluctuating, misfiring, throwing DTC's/codes. He had it sitting there for 3 months. His wife wanted it gone.
82571
yes, that's how it came out when I was changing old ones with new ones.
 
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