I’m looking for technical help or recommendations on: Spark Plugs
Hi, I have an odd situation and would like see if anyone has experience on the topic.
I have a new-to-me, 2010 NC Sport 2.0 approaching 100K. It has Mazda FSH with the original supplying dealer and they apparently did the plugs at 50K. I thought I would change the spark plugs now, a bit earlier than the schedule as it just doesn’t seem smooth at slow speeds, revs seem to fluctuate at 2300rpm. Most noticeable if you want to crawl along in 2nd, it feels like it repeatedly ‘bounces’ up about 200rpm on top of what you’re holding. Other than this, it seems to accelerate and idle ‘OK’, but then I have no experience with any other MX5s to compare it too. No error codes using OBD reader.
I looked up the spark plugs on NGK site, and was suggested ILTR6A-13G. All threads here on OC seem to back that up. I ordered them.
I pulled out the existing ones and compared side by side with the new ones. They are a lot shorter than the new ones! Old 17.5 mm, new 25mm. The existing ones are Mazda TR5AI-13. My research shows they are NGK and suitable for the 1.8 only.
Overall this points to the wrong plugs being in it and I have the correct replacements, but obviously you can imagine I am apprehensive to put the new longer ones in
Should I slap them in, turn the key whilst looking the other way pulling a funny face and flinching slightly? Or any reassuring tips?
Go for it, it seems the incorrect plugs were in it. Check most other suppliers and it comes up with the 25 mm reach plugs for the NC2 2litre.
Can’t say I’ve changed the plugs on my 2 litre, they were done 25k miles ago by the Mazda dealer.
I presume that you do actually have a 2.0 Sport with the correct Sport spec and not a specced up 1.8. Just a thought as I can’t see why a main dealer would make that sort of mistake, on the other hand maybe they are that bad. Just goes to show. Care to name the Dealer?
I’ve just checked and, yes, the plugs I put in my 1.8 are NGK TR5AI-13, 17.5 mm or so thread length. FWIW the car was running perfectly welI, but I changed them at 40k as the car was 11 years old. The old ones looked absolutely fine and frankly it didn’t make a scrap of difference.
JS
I think so, all paperwork normal. Car just looks standard and fair for the age and mileage, no garage queen in my budget unfortunately, I wish I read here engine number very hard to get to, but they mentioned 2.0 has VVT solenoid on the cam cover, and it does. The service history record for the replacement was 2016, so I don’t think I will name them if it’s just one dudes mistake. I really hope it is, then it’s easy fix
Thanks, that is great information. I have been scouring the forum, and I think I saw this (when just planning jobs I was going to do before I even received the car) but didn’t tie it altogether.
“The low rev, low load coasting stutter” is a good description. The ‘low load’ is really key, that is when it feels particularly poor to drive.
This is giving me the confidence to do the squinting start I should pull the trigger in the next couple of days, and you’ll either see a post for “2.0 engine needed cheap”, or success
Can’t you look down the spark plug hole and estimate how long the thread is? Maybe push a screwdriver in to use as a sort of depth gauge. Assuming you you don’t have a vernier caliper to measure it properly.
It ‘looked’ pretty deep in all 4 but I didn’t stick anything in there, it’s a bit like looking into the sarcophagus, I’m just getting comfortable with various mechanic DIY
Thanks I really appreciate all the responses and input! Definitely encourages me to join the club! I’ve found with other cars, the OC makes a big difference to the ownership experience.
I have just been out replacing the spark plugs. All went smooth for all four, to a low torque. Haven’t started it yet as it’s late, going to do that tomorrow and report back. I also changed the aux belt so a few things are getting tested at once…
All 2.0 have the same length plugs - the long ones.
It’s other engines in the MZR range which are different, some 2.3s have the shorter plug. I have no idea why either, there is no obvious reason for it.
Great, thanks for the information, confident in the size now with all the reassuring replies. Been too busy with work to even get outside and start it up, but I will do it tomorrow
Whether it’ll cure your issues or not I don’t know, but it will run better one way or another. More power and more MPG as the spark is now in the right place rather than halfway back up the threads!
If only the last guy to go in there was as vigilant as you.
I read here engine number very hard to get to, but they mentioned 2.0 has VVT solenoid on the cam cover, and it does. The service history record for the replacement was 2016, so I don’t think I will name them if it’s just one dudes mistake. I really hope it is, then it’s easy fix 
