Recently an ignition coil pack failed hard (limiting vehicle speed to 5 mph and throwing a Check Engine DTC) at 83,000 miles on my 2019 Mazda CX-5 Signature. For the past year and a half I had seen deteriorating engine idle symptoms, especially at cold start idle with the transmission engaged but it would not trigger a DTC. Even when the coil pack was initially failing to the point of reducing my ability to accelerate, it would not trigger a DTC, at least not to a simple OBD2 reader. While the dealer replacing the coil pack did solve the hard failure symptoms, I still had left over rough idle issues, just not as accentuated. On a hunch, I bit the bullet and replaced the other 3 coil packs (with OEM) and lo and behold, my engine purrs like it was new. Absolutely rock solid idle. This is only my second vehicle with coil packs, the first having 150,000 miles with zero coil pack hard failures, although that engine has not been idling at its best, either. Has anyone else experienced these ignition coils slowly degrading where they become somewhat predictable when to replace although not triggering a check engine light?

 

These really from a performance stand point start showing less supportive energy at about 50 k miles or sooner. However unless the use of an oscilloscope is used to see the performance most all DIY think the coils are fine and comment about them going trouble free for decades or more then 100k miles.
The other reported or none reported is no directly associated DTC to a coil. This is also a misdate made by mechanics and so many DIY that just do not have proper tracing of Diagnostic trouble shooting.
Then we have the almost total lack of maintenance for the coils. Yes maintenance. The springs and seal frequently need to be serviced by way of replacement. Last is the ridiculous practice of going extreme miles on the spar plugs because the service quite give you the recommended service miles or the spark plug manufacturer claim the phrase Get up to miles having to do with the service life . Here again unless you use a scope you are guessing and as that spark plug needs higher energy to fire it demands more from the coil. The stock as well the best coil replacement really are low quality performance wise and the out put energy is relatively less the some may think, all have an influence in the service life of all the ignition systems parts.

last there are areas in the ECU that will have stored DTC that get placed in a permanent file but may not generate a DTC.So if a coil may have indicated a problem but was not constant then a DTC would not activate the check engine light and the minor or anomaly caused by a coil degrading may have not shown to be enough at that time to pop a DTC and check engine light. So again to an untrained mechanic on diagnostic troubleshooting they would not know or have a reason to look beyond checking for correct DTC. And forget about a DIY knowing most any of this?

Here a question I don’t expect anyone to answer or admit not doing but do you use dielectric grease when replacing the spark plug and cleaned the coils before reinstalling them. That’s another subject and more possible coil energy going places other than to the spark plug. Lol

 

see post # 441 and 442


https://www.mazdaforum.com/forum/maz...-44018/page44/

 

Thank you for the detailed response, Callisto. That was very informative and interesting. Since I wrote this, I’ve been tracking my fuel consumption rate and it has increase by 3.5 mpg! Not trivial. I also replaced the 8 coils on my 5.7L Hemi Jeep with 150,000 miles along with the spark plug wires with amazing results (I used NGK vs Mopar). Everything you’ve said definitely is right on in that we think these coils are just fine and last a lifetime but they really don’t. And all those different failure modes. I’ve always wanted an automotive scope but they’re probably pretty expensive. When I was trying to install cylinder number 4’s coil on the Mazda, it wasn’t seating so I took off the plug thinking maybe there was some interference. I noticed the plug was black on the bottom round rim, basically carbon from unburnt fuel. Should I replace those plugs?

 

Can u provide a couple of pictures?

 

Here ya go! Picture of cylinder # 3 spark plug that has 5000 miles.


Also, I forgot to answer one of your question. On my first spark plug replacement around 38,000 miles I did use dielectric great. I found it made it very difficult to insert the boot over the plug given it seemed the air was trapped inside the boot and would not seat properly. When I replaced the coils just recently I used a little dielectric grease on the tip of the boot.

 

The plug may be on the rich side but then it depends on how long the engine is run at low RPM and also how many seconds it idled before you pulled it. In which case the other indicator would be normal fueling and timing and not a mechanical concern.
Dielectric grease needs to be used sparingly and properly to do the correct protection but nut cause an electric barrier.
look at the last page of my thread
https://www.mazdaforum.com/forum/maz...like-do-44018/

Back to the plugs, if the other plugs all looked like this then you should be ok. But if not then you should do at least a compression test on all cylinders. If you do that make sure that all the cylinder do no more then 5 rotations no more and no less to be accurate and accurate to compare .

If the highest comparing the lowest is more then 10 lbs I would consider to do a leak down test as well

 

Thank you, Challisto! All the plugs look the same so, good for now …

 

BTW you can actually clean those spark plugs with a little soaking of carburetor or throttle body cleaner and a soft copper brush. They could be used for another 3-5k miles unmeasured?







For some that may question this method of cleaning, it was widely used for decades to spray "GLAS BEADS" on spark plug to completely clean then of all carbon and other contaminates and was never shown by way of testing on a scope to hinder the performance of the spark plug. In fact, comparing a before and after cleaning often shown an increase in the spark kernel and spark energy.
Sadly this is a lost service art now because its easier to just spend the money and buy and change new spark plugs.
For those using Nitrous we all know the 2 second spark plug cleaning method... LOL