OK, bear with me please. Done hundreds if not thousands of spark plug changes, but first Mazda, first "coil on plug" vehicle, and first ever time with issues. Looking for what must be obvious that I have missed. CX5 2.5l Turbo, 2019 model.

Simple plug change - or so I thought! Unbolt and move plate with all the hoses/stuff on it to get to three of the four bolts holding the coils on, remove all 4, new plugs in, all good.

Go to put the coil/boots back on, #1 (Left hand side of engine, looking from front, in case this is actually #4!) pops on, seats easily, does up fine. No issues.

#2, #3 and #4 go on, but are 5-10mm adrift from the brass insert that the should sit flush with to put the retaining bolt back on. Swapping with the one that fits #1 produces the same result on 2-4. Swapping back to old plugs in case, same result.

So, thinking maybe they just need to be bolted down, I do that, go to start...horrible misfire and stall. It's as if it's running on way less than 4 cylinders. Old plugs back in to check it's not as simple as bad new plugs, no change.

Went from running perfectly to misfiring and stalling. So other than needing to find out what I did/missed, I can't help but think it has to surely be related to the fact three of the four boots fit poorly for some unknown reason, and I didn't notice it when i took it off.

Checked several YouTube vids, and no mention of anything special, none of them did anything different to me, and none seemed to have the fit problem I do!

So, please, someone put me out of my misery - have I missed something stupid, and on this engine is it normal for the coils/boots to need to be pushed down and held then while the bolt is tightened, but only on three of four cylinders? It's driving me nuts because there should be nothing difficult about this.

Many thanks!

 

Ok so when you start a help me thread please post the year model and transmission type or what is important related to your question just like if you filled a service order at a dealership or shop or were to go into a parts store to buy a part?

Even simply spark plug changes vary on platforms and models and years.


I could tell you that if you removed parts and reversed the order then you damaged a part unknowingly. Based on what you wrote you should have a check engine light and can check what DTC you have which "may" give a clue to what happened.

If you did no exaggerate a bit on how many sparks plugs you have changed then my guess is most were with spark plug wires. Then you should well know that a new spark plug does not mend a failing or aged coil or spark plug wire and the simple act of pulling on the wire can unintentionally damage it internally and you get a misfire or poor performance after you changed your spark plugs. It is an example of easily overlooked service work.

 

Welcome to the forum

 

As Cali said it is difficult to give any advice without knowing exactly what you did and how you did it.
Modern vehicles are not for the average DIY person.
Even spark plug changes, a once simple task, can require specialized tools and the removal of a whole host of parts just to gain access to them.
Each of those parts with the potential to cause an assortment of electronic issues and error codes.
The cost of the tools, diagnostic equipment and actual knowledge needed is beyond the capabilities of the average "weekend wrench" as you found out.
While it can be expensive to use a local garage or dealer the work is stress free for you and if they screw it up the costs to repair are on them.
At this point I'd bite the bullet and get it towed to the garage/dealer and enjoy a cold beverage of your choice as they do the work.
Otherwise, you could be hours, days or who knows how long figuring out what is wrong and even then, still not be able to fix it.

 

I did - from my post: CX5 2.5l Turbo, 2019 model.

Was there somewhere specific I was supposed to put this in my profile?

Yes, but this was simply pull coil/boots off, swap plugs, replace coil/boots. Short of unknowingly damaging a wire, which I'm pretty sure I didn't, or knocking something else loose, that is what is so confusing here. Don't recall an engine light, but will re-check and also borrow a code reader and see if there is anything new there.

Again, yes, and no real exaggeration over 40 off years of working and playing with cars, bikes and small engines....but as I said, and you guessed, this is the first time doing coil on plug work. Less chance of pulling and breaking wires though, as all I did was undo the coil, and lift it and it's boot off the plugs, then swap them.

There was nothing wrong prior - this was just a plug swap as the service schedule called for them to be changed, so whatever I did has to be the cause.

So what I was really hoping for re my queries was a CX5 saying something like "Yeah, you need to do this" or "Yes, that weird fit you described is normal" or "No, shouldn't be like that, and it's probably what's causing the issue" type thing.

Anyway, thanks for the comments and the welcome!

 

It’s easy to over look and damage the boots and internal coil terminal in the boot.
I think I was making a point that asking for help to supply as much as possible about your vehicle. I posted the very basics, but did if you read said as if you were filling out a service work order.
As for suppling information aside from the usual which is the basic the miles and last services done and at what miles is important ?

DIY often think that changing spark plugs on pre electronic ignition is nothing special but my guess most often did incomplete and often over looked supporting parts when only changing what they thought was simply plugs wires points and condensers .
Most never actually checked the ohm resistance in spark plug wires in service let alone new from the box assuming that new is always good . 😂
And don’t get me started on gapping the correct way and what is the optimum gap and how to determine that as well selecting the best heat ranges for how the engine is used.
how many spark plugs someone has changed in their life does not measure a total level of experience.
If that were the case when I raced professionally the plugs were changed every run, so doing the quick math that would my one not all S/G Camaro during a 6 year span Iam pretty totaled more then your estimated of how many spark plugs you have changed on all your vehicles in your life ?
Funny if I tried to even add how many for customers since 1977 it would like , hmmm let me put it another way several hundred pounds of spark plugs lol.



Back to your problem, on that year Mazda you should find in the ECU pending or permanent DTC as well the I/m will be in fault. And if you go deeper you can check the counters to see how long the issues were being reported to the ECU. This will give you the map for finding the issues unless it is mechanical.

If it is mechanical then the first thing is to do a “properly performed “ compression test. This will indicate the possible need for a leak down test and possible scope of the intake system and cumbustion chambers.

You could skip a lot of these steps by doing an oscilloscope test diagnostics . This will tell you exactly the short coming of ignition fueling and even a weak cylinder. You would still need to confirm and check the ECU history and information.

 

Spark plugs replaced but misfiring etc. If you have tried all of the above then as a last resort, try replacing one or all 4 coil packs or try to swap coils and listen with stethoscope and then repeat changing coil to a another plug, until all 4 listened too to see if you can isolate problem. See utube video on plugs trouble shooting.
most likely bad plug or coil.
if you purchased plugs online at ebay, then fake brands!! See TDK website for issues on fake plugs. Buy always at Dealer.

 

NO do not swap coils for testing! This poor advises form DIY that read to many www YouTube how -to. Doing that service procedure is sure to cause other problems or cause failed parts!
There are to many BAD service recommendations that should not be used, and this response is an example of some of the WORST possible ways to find a problem!

Befoe you respnmd in your defence please tell me what your recomendation will have effect on the ECU?
If you know that you would NOT have posted that poor information service procedure.

BTW DEALERS over the years have had inferior parts manufactured and distributed to them unknowing. There are almost NO auto manufacture in the world that manufactures their own spark plugs anymore.
As for experience about spark plugs in my lifetime my guess is I have sold over 10-15 thousand or more of them Yes that many! And never have I gotten a counterfeit spark plug!
ASE
(FYI these are not my initials in my name)


hey I bet you are entertaining to your Doctor or Dentist telling them better ways to take care of your body or teeth from those ytube DIY you watch? LOL