I agree with other people in this thread that this is an issue that goes beyond the plugs.

Mostly people seem to say the plugs (assuming they aren't loose) last longer than the ignition coils.
Still I can't help but read this thread and think about the other thread where the person had a rat chewing through wires under the battery.

In any case like Pyts says, check the oil. Maybe it goes beyond electrical problems.

this may be silly but.. do you still have your plastic splash guard under the car? Has there been a lot of rain or any kinda scenario where stuff in the bay got really wet?
​​​​something like that could also cause your symptoms, though I'd hafta slide under the car to see vulnerabilities.. would a voltage drop help lead someone to a thing.. ill go get the manwell and see what troubleshooting has to say.

This is the rabbit hole though, sir. Just imagine alice in a world of wires, lead solder, and electrical connectors in really hard to reach places with the squeeze-to-release tabs but they're super stiff.. it seems dumb basic, and even unlikely, but checkin that oil is like checkin a persons heart rate. Just protocol.

Another datapoint 20LB/FT from Chiliman

Final Update (hopefully):

Took the car to my mechanic and the car stumped them for a while. They did the valve adjustment and it didn't work (needed to be done anyway). Checked fuel pressure, coils, spark, compression...all checked out. Then he suggested that the computer might be bad...so I found a used one from a local salvage for $160. Had them install it and boom, car works perfect again. Didn't charge me for troubleshooting either, as I send them a ton of business. All in all it cost me $500. Hopefully I get another 100k out of this old girl.

I checked the plugs on our 2013 with 72k that we just got and they were all perfect with no by pass. I checked the torque when removing them and they were at 18ft lb, so I put a little anti-seize on the new ones and torqued them to 18ft lbs. I figure if that worked before, it should work now. I was doing a valve adjustment so I figured I may as well replace them while I'm there.

Interesting to know about the computer issue.

First post for me on the forum. In the world of pandemic and isolation, my wife and I decided that after 17 years of no car in NYC, it was time to bite the bullet and get a car for at least the next six months. The research led me to FITs, and then eventually the 2009 Sport with 120K miles on it. I picked it up from a NJ dealer last week. That is a whole side story, which I'll post about later!

Anyway, I took it into a friend's highly recommended mechanic in Park Slope, Jerry Atros Motors, and they did a thorough going-over of everything. They had to use an antiseize to get the plugs out, and long story short, found corrosion and we ended up replacing the plugs and coils, (and the serpentine belt and the blackish brake fluid).One plug was in fact loose but nearly impossible to turn, and it was by all a reports a pain to remove. And it turns out the starter solenoid is on the fritz, too. That said, other than these things, which are repaired or about to be, the car is in fine shape, and we've been assured by the mechanics that we could confidently drive the snot out of it with no worries.

Anyway, now that I've been reassured we don't need to worry, I'm excited about the Fit!

Congrats on the fit you will love it!
I’m sorry to be the bearer of bad news, but if the plug was loose the damage is done, it’s only a matter of time before it becomes loose again or blows out. In my experiece, mine kept coming loose until it finally blew out. The good news is this is not that big of a deal I was able to repair it easily over some beers and picked away at it for a couple of hours in the garage. The mechanic is correct you can beat the snot out of it without worry, these engines aside from this stupid spark plug issue are very durable!

I'll talk about the loose spark plug later, but is it possible that this car was under water? I run motorcycles and sometimes we're in deep water. The engine is hot, so any water around the spark plug gets baked out right away but some corrosion happens. Also, the brake fluid (rear especially because the reservoir is lower on the cycle) can get water in it and get milky. If your engine was under water, the 'cups' around each spark plug / coil pack would fill with water and then proceed to corrode all the points between each component, as you described.

The mechanic probably used 'penetrating' oil to work the spark plug(s) out of the cylinder head. 'Antiseize' is something different and used during the assembly process.

On that odd spark plug, I'm 50/50 on. Run the car but if you get a check engine light, check all of the spark plugs. Just because that one spark plug was part way out doesn't necessarily mean the threads are damaged on the head, which means that it's 'impossible' to ever keep the one tight.

My '11 Sport AT #2 & #3 worked loose and I did everything by the book on reassembly with new spark plugs, proper torque specs, etc, but they came loose again. I then used a little bit of blue threadlocker paste (Permatex) on each plug and they've been good for the last 30k miles. Maybe I'm just lucky but it worked.

On the car in general, I'd snoop around your easy to reach electrical connections and disconnect and inspect for corrosion, which might be additional signs of it being under water. You didn't say if it's an auto or manual trans but check that too. If milky, that's a sign of water. What does the engine oil look like? Same thing there - milky means water.

Report back. I don't want to be a 'chicken little' and will gladly change my opinions if proved wrong.

This seems like the me-too thread, but I just got my 2013 5mt (70K Km) back after having plugs, coils and injectors replaced. Plugs not covered and cost quite a price to replace up here in Canada, not to mention they had to come from Vancouver all the way to St. John's (literally from one side of the country to the other). I suppose the plug change was pretty early, but if they were in there...

Started with a P219a code (cylinder 1 issue ) and a rough idle; I was a little relieved to see the code where it's still covered until next May. Next thing there were two plugs which were finger tight and dirty injectors. Those plugs sure are something to keep an eye on, aren't they?

Wow, changing out the plugs / coil packs / injectors at 43,500 miles. Hope it works out. As noted in my other posts, I'm able to slow down, do somethings myself, and save some money.

I bought an '09 a couple months. I had read about the spark plug issues on here. The one I bought has had its spark plugs and coil replaced a 3 years ago. Is this an ongoing problem that I need to keep an eye out for or once it's replaced they should be fine?

Although I don't have a 'scientific study' in hand, I'd say 99% of the time you get a misfire code, it's a loose spark plug. I also believe 99% of the time, the coil packs are all good and have nothing to do with the problem. I can't remember anyone posting on here saying that a coil pack was the problem, just loose spark plugs.

BUT, if the spark plug has been loose for any length of time, the escaping hot exhaust gases will damage the spark plug threads in the head and the coil pack's rubber boot and snot that all fits down in and around the spark plug to the point of needing replaced. The coil pack's electronics probably isn't damaged and will probably go a lot longer than 100,000 miles.

Again, I have a '11 Sport AT with ~87,000 miles and had loose spark plugs around 36,000 miles. I eventually used some blue threadlocker paste on each plug and haven't had any problem since the mid-40,000 mile mark, so no spark plug problems the last 40,000 miles and I'm still using the original coil packs.

Indeed. The fact that they work themselves out is still a bit mind-boggling to me. I'll be using some thread-locker blue when I check the plugs next time. I know I paid a bunch to change the plugs, but at least I got a fresh set of coils and injectors out of it, right? :)

original torque spec was 14ftlbs, the revised one is 20. I don't recall hearing back from anyone who fixed that error. Some add thread sealant, some advise against reusing plugs once they've been removed.

Well I'm hoping the mechanic just tightened the heck out of them without looking up the torque spec.

I changed my plugs out back in July of 2017 with around 100,000 miles as part of my general maintenance schedule. Good thing too, since the #3 plug was starting to come loose as evidenced by the sooty boot on coil pack #3. It's strange that the spark plug #4 looks like the one that would have been loose with all the brown spots on the insulator, but it was perfectly tight.

Anyway, I swapped the plugs out three years ago, put some anti-seize on the threads and then overtightened by feel to what is most likely more than 20 lb-ft, cleaned up the coil packs, and haven't had an issue since.

-Rob

https://cimg3.ibsrv.net/gimg/www.fit...fcca0001e.jpeg

Thanks for sharing. My #2 and #3 were the lose ones but #2 was worse, and therefore, had the sooty coil pack. I'm still using the original coil packs too.

I got tired of those clips that hold the L Shaped pieces, so I screwed them down.

Many years ago I serviced and calibrated aircraft shop equipment, including torque wrenches. I found out that price was no guarantee of quality in torque wrenches. It is a good idea to periodically have them checked and adjusted.

I saw a youtube video with a guy using a Snap-on torque wrench tester. I think it was Snap-on. Tells you if your torque wrench is out of spec or not. Don't know what you're supposed to do from there, but it looked like a good tool to me (unless the tester goes out of spec :D ).

torque wrenches can be repaired and adjusted. I used a tester that had a fitting to attach the wrench to and a big dial that read what the actual torque was. We sent it to be tested and certified every couple of years.

It seems that this loose spark plug issue is somewhat common on the 2nd gen Fits. I had my eye on a used 2013 sport (120k miles) but now I am not so sure. Does owning a 2nd gen Fit mean I will constantly be tightening my spark plugs to keep them from blowing out?

Does anyone know how well the blue threadlocker will work long term? Could this further damage the threading when spark plugs eventually need to be replaced?

That's what I figured. My point is that you need a torque wrench manufacturer to repair and adjust. Not something for Mr Home Mechanic.

My sense is that it is somewhat commonly reported on the Internet. Not sure if it is somewhat common versus the total number of Fits manufactured and sold. Also not sure of it is somewhat common on cars direct from the factory assembly line, or somewhat common on cars where someone has monkeyed with the plugs inappropriately. GAFIT has posted that the problem is related to the number of threads on the spark plug. I haven't heard that one before, but it could be correct. However, if it were a plug thread issue, it would be easy for Honda to acknowledge and correct, but Honda, as far as I know, has denied that there is a spark plug issue. At best, they have said it's a torque spec issue — which means there is post-manufacturing human error somewhere.

Loose plugs
 

I just pulled mine after changing them 5000 miles ago. All but the number two plugs were loose! Number 2 plug was tightened by me a couple of months ago so it was still tight. Three out of four indicates a problem! I used blue thread locker on them and installed them again. From what I read the blue is the correct type. Don't use red, that is for permanent lock. The spark plug saga continues, I'll keep you posted on how well the blue thread locker works but I have no plans to pull the plugs to check for tightness but I may check number 1 plug since that can be done without pulling the cowling. Best of luck Clay

Loose plugs
 

I should mention that I almost didn't check the plugs for tightness. I was just thinking that the number two plug was not really tight when I checked it a couple of months ago. This should be a warning to all of you guys, check those plugs and you may be surprised at how loose they are! I installed the new plugs and tightened them to 25 foot pounds and they were loose when I checked them 5000 miles later! Best of luck, Clay

Interesting. As the head threads oxidize and get contaminated, friction rises. So factory torque specs which might be ideal for factory-fresh threads become dicey. The extra friction on the older threads could effectively reduce clamping force (significantly) for a given torque. Anti-sieze coatings included on new plugs could mitigate this, to an extent.

Also, torquing well over factory (revised) spec on a aluminum head risks damage to the threads.

Personal speculation so the views of a professional or specialist would be welcomed.

Loose plugs
 

Anti seize might help by sealing the threads from exhaust gases. Any threaded item with anti seize would have less friction and thus be easier to remove. That is what it is its intended use. Mine were brown from escaping exhaust gases so that must be the root of the problem. The thread diameters in the heads must be off a little and that allows gases to permeate the threaded area and loosen the plugs. That is my theory anyway. If your waiting for an official response to solve this problem you will have a long wait! I think thread locker makes much more sense. Best of luck Clay

Got one other idea. I'd like to submit for your consideration installing and torquing spark plugs only on a cold engine, same way we treat a valve adjustment.

Loose plugs
 

I don't think the torque level is the problem. I used 25 foot pounds on mine and they came loose so just use 20 foot pounds like the new specs sounds good. Need something to seal the threads. Perhaps conductive thread lock would be best? Does it exist?

I used permetex "copper spray a gasket" head gasket sealant. It may be a 🐝 to clean out, not sure, but it's.. exactly what you asked for. Haven't checked my plugs since, just the nuts on the coils by hand to make sure a backing out plug hasn't broken them loose, but my engine is whisper quiet.
https://cimg2.ibsrv.net/gimg/www.fit...a8002bf203.jpg
Available from any autoparts store, most expensive on amazon. cheap from summit racing and ebay.
It's a high temp adhesive version of anti-seize meant to seal imperfections between metal head gaskets and cylinder heads and promote temp transfer.. which it says on the can.
I can't find record of anyone else using it for plugs, but I'm pretty stoked on it.
Also, just so we know we're not alone, F150s around the same age have the same issue. Not enough plug threads, plugs ejecting. :popc:
I don't yet know how or if i'll need to clean it out when my change is due at 30k miles (denso ik22s have a shorter life span according to denso)

Loose plugs
 

That may be better than blue thread locker. Temp range up to 500 degrees! Blue thread locker works but this may be better still. Nothing noted about electrical conduction properties but its copper infused so that sounds better. Can the plugs be pulled out afterwards though? Please let me know how that goes. Thanks for the suggestion. Best of luck Clay

It's likely going to be quite a while before I pull the plugs, but the gasket aerosol lays similar to paint, just sticky like flypaper. I'd be quite shocked if it could stop removal.
I'm not sure what you're driving at in regards to electrical conductivity. To coat my spark plugs (this process is messy) I did something like this
https://cimg6.ibsrv.net/gimg/www.fit...5be38e149c.jpg
https://cimg8.ibsrv.net/gimg/www.fit...be4ff37291.jpg

Just getting the threads.

Actually I found out you can. Google it.

Loose plugs
 

I was referring to the electrical connection between the plug threads and the motor. Blue works fine for this but copper spray may be better because it sounds more conductive to electricity. Testing all of this is a problem since the cowling has to be removed to check the plugs. Even if your plugs cant be removed it may not be a real problem since these plugs last so long. My car had 120k miles before I changed the plugs and had no misfires at that! So you now have 120k miles on your new plugs anyway so why worry about removing the plugs? Best of luck Clay

Just adding my experience to the list-

2008/9 GE8 Thailand built L15A7 Manual. 97,000km

Was on a roadtrip, cruising down the country hwy at 110kmph, and all of a sudden hear a clapping sound come from the engine - initially though maybe the accessory belt broke and was flapping about or the undertray broke.

Immediately pull over and the engine is struggling bad and a loud flapping noise with engine light on. I thought either a miss or maybe a bad exhaust leak.

Get it towed to the nearest town's honda dealer because I am hours from my city. The service counter lady say the mechs have diagnosed it as a spark plug coming loose, or even out? and has also killed the coilpack. So they then installed a new sparkplug and a non-genuine coilpack. Show me a print out of the error code, saying it was cylinder 4.

I had replaced the plugs myself around 45,000km and 4.5 years ago - use the NGK advised procedure of doing them handtight and then 2/3 more of a turn to crush the sealing washer thing (i have installed plugs on many cars with never an issue). I guess from now on I will check and torque them every 20,000km.

For a few months before this incident my idle had been a bit low, around 550rpm, and a bit of vibration. I thought maybe a minor miss or an engine mount was worn. Maybe the engine was a little louder too. I was going to look into it, thinking to check the coils.. so prehaps it was actually the sparkplug already a bit loose and not sealing properly. With the new one installed the idle is back to 700rpm ish, but could possibly be the resetting of the ecu too.

While you have the time, I'd check everything - all four spark plugs. My #2 & #3 were always the issue.

yeah, when i have time i am going to pull out the new plug to ensure the thread is fine... if its fine i might get 4 new plugs and new coils

Not sure why you'd be so quick to change the coil packs when they aren't the problem, plus one is brand new. If a spark plug is leaking for many miles, yes, the escaping hot exhaust gases can damage the coil pack and I would change it, otherwise, I'm not sure that they go bad.

After a dealer scammed me and replaced the coil pack ($55 diagnostic, $160 coil pack, $55 labor), check-engine-light came back on the next day (same spark plug was still loose) and they recommended bring it back (more $$$). Luckily I had asked for the return of original coil pack to my car that they replaced. After inspection, covered in gasoline smelly soot, I surmised that it was a leaky spark plug (new to me at the time) and never the coil pack. I changed all of the plugs and reused that original coil pack to prove a point. Everything continues to work fine ~40k miles later, except the #2 & #3 plugs came loose again (~5k miles later), so I used some blue threadlocker, and had no problems since.

well i ended up having a look.. and the spark plug that blew out seems to have taken 60% of the thread with it.. I didnt want to bother and risk trying to rethread it. so just got a replacement engine and put it in, and did a new clutch at the same time.