"Many carmakers require iridium spark plugs or iridium/platinum combination spark plugs for (COP) ignition systems. If your owner’s manual specifies iridium spark plugs, don’t downgrade to platinum spark plugs, or double platinum spark plugs, or even copper spark plugs. They won’t perform as well as the iridium spark plugs in this case."

Source - https://shop.advanceautoparts.com/r/...en-spark-plugs

Make sure you are comparing performance plugs to other performance plugs.

The old standard platinum plugs are not better than copper and copper is still the best material for transferring energy.

The problem with copper is it is soft and the tip has to be larger. Iridium plugs are able to get away with a tiny tip which provides a hotter spark. Generally speaking, switching to iridium allows a larger gap. In addition, you can usually run higher output coils without melting the plugs.

Most late model high performance cars are now using iridium because of it's ability to handle higher energy systems.

https://dragillustrated.com/performa...lugs-from-msd/

It's possible that the factory Honda coils are even too strong for those copper plugs.

I suggest you change out the plugs for a set of performance iridiums and see what happens. I think you will be surprised.

Also, I base my knowledge on a chassis dyno with my own car. It made 11whp more with a switch to the same heat range plugs, but in Iridium. Other boosted Mustang owners find the same results and I'm no longer having to change plugs constantly (car made 532whp).

 

These right here. "Exact fit for your: 2010 Honda Fit." Copper core, nickel tip. Exact same composition as the NGKs. Am I not getting something here?

 

I don't have experience with the E3's. I always thought of them as a marketing ploy, but I could be wrong.

I have only track and dyno tested NGK copper and NGK iridium plugs, so I can only comment on those. The iridiums made more power and are holding up considerably longer.

 

My suggestion, since it takes all of a few minutes to change them...put the other plugs back in and see what happens.

If it's better, then order a set of Iridiums in one heat range colder than original.

If it doesn't improve, start searching for other possibilities.

 

I had a similar problem with my old car. The dealer chastised me for the non-OEM ignition coils I had used in my car. He went ahead and installed OEM ones...and then the car was down on power and sluggish. Turns out the OEM coil was bad.

 

X2

That will settle the issue....

 

Hmm... Maybe? My reason for replacing the plugs was that I was beginning to experience some hard starts, but I guess that could be either. Seems weird that the problem would get worse on the same coils with fresh plugs if it was the coils, though. Also they're more expensive and I'm gonna try the cheap thing first

 

Yeah, that's my plan. Unfortunately I don't have a garage right now so I have to wait for daylight, and because of my current work schedule that means I have to wait for the weekend. Just wanted to do my due diligence in the meantime.

 

Good luck!

Another possibility is that one or more of the coils didn't seat quite right. They can be finicky even with using dialectric grease and doing it right.

Also check for signs of carbon fouling on the coil boot. We have one "weak" cylinder on our Fit. The plug threads aren't perfect and that cylinder contaminates the plug boot.

Thankfully, ours hasn't ejected the plug or anything drastic like is known to happen with GD Fits.

 

Well, I made it worse. Replaced the NGKs with E3 56s, which are a guaranteed fit according to AutoZone, advance, O'Reilly, and many posts on this forum. Gave it a test rev, and now it's acting like it's hitting the limiter just short of 5000. What in all of the fuck.

EDIT: Nevermind, I'm an idiot. Didn't know about the neutral limiter.

 

HeeHee, you need to gain some confidence in your abilities....

 

Just got back from a test lap with the E3s, and everything is golden. Still irritated that I can't figure out the difference between these and the NGKs, but at this point it's running like new so I'm just gonna call it.

 

Please give us and update after a few thousand. I'd like to hear if the MPG are in range.

At around 26K, my #2 / #3 plugs were loose, smelled gasoline in the morning upon start-up, gas mileage plummeted.

 

1- High test gas doesn't make your car perform better and "racing" spark plugs won't automatically make your car perform better.
2- Race car engines are torn down and rebuilt very often. Racing plugs only have to last one race. You might prefer your plugs to last longer.
3- Changing the heat range when you have not not changed anything else in the engine might cause problems.
4- Changing to a non-resistor plug can sometimes cause rough idle or misfire. (Every car is different.) In addition it causes more RFI (Radio Frequency Interference) which, in turn, may interfere with your radio, onboard computer or other electronics depending on how well they are shielded and grounded.
5- "Guaranteed fit" means just that. It will fit but it may/may not be the best design for your particular engine setup. (How in the world would they know what mods are under your hood?)
6- Unless you can hack or upgrade the car's computer, the OBD software will constantly monitor external environmental conditions as well as engine operating conditions and attempt to return to the factory preset "preferred" performance. The computer might interpret your "improvements" as poor performance and adjust its settings (timing, fuel mixture, etc.) backwards in an attempt to compensate.

My wife's car (2009 Fit Sport automatic) is a daily driver, so reliability and ease of maintenance are most important to me. My OEM NGK iridium plugs lasted 140,500 miles and they looked like they would go at least another 50,000 miles. They were a real PITA to replace due to lack of easy access. (Behind the engine & under the bulkhead/dashboard.) One replacement every 6 years is enough for me. I installed the Denso 3401 plugs ($8.36 ea, Rock Auto) three years ago and the car has been running fine with no change in performance or gas mileage.