Aging coils, ignition question
 

Not sure about how they fail, but I had similar concerns for my car.

Why not upgrade the ignition system to a more modern one using smart coils? If anything just for the reliability and longevity of the ignition system.

It's probably better than putting money into OEM replacement ignition components that were designed 20+ years ago.

I have seen bad coils before, one (leading coil) was bulging on the side and had an obvious internal failure. Don't know if this was caused by something the owner of the car did or what. I also have seen coils that looked fine but didn't pass the test or didn't work properly.

The shop manual has a good test for coils by checking the resistance. In my experience if it passes that test the coil is good. If the resistance is drifting towards being out of spec that could be a sign of them going out.

If they work fine and pass the test, just keep running them. On your setup I don't see a good reason to invest big money into a whole new coil setup. Heck, even if you did have one go out, you could probably pick up a good used low mileage coil pack for cheap, swap it in, and have another 10 years of life.

Dale

ive seen a few bad leading coils too, some percentage were due to spark plug wires that didn't fit right.

I can see that happening with crap plug wires. Stock NGK wires are dirt cheap, fit and work great, no reason to try and use something else.

Sgtblue, if you want to go the extra mile you could pull the leading coil and do the resistance test in the FSM. If it's dead in the center it's in great shape. Getting low or high then it may be showing its age.

Dale

IMO, be careful with the FSM testing of the lead coil. This is for true failure rather than simply a weak but not yet totally failed coil. I had my original stock leading coil cause a major catastrophic detonation event back in 2014. I was at half throttle on a cool 45 degree day with no heat soak at all and blew up my engine at around 5 psi. Chris Ott at RP searched for the cause after he rebuilt my engine and could not find the cause. He changed my fuel filter, changed to a new RP fuel pump (I had a relatively new RP pump before the blow up), he added the ignition wiring bypass mod similar to the fuel pump mod I already had, checked the coils as per the FSM, and looked at everything else he could think of with no cause determined. It wasn't until I got the car back that I had the coils rechecked by an engineer friend of mine in a lab. He found the lead coil would, on rare occasions, simply discharge on its own after being charged with no ground removal to signal the coil to fire. We believe this was most likely the cause of blown engine, particularly at such low boost and cool intake air. Also, the lead coil is the most used of the three coils having double the number of charge/discharge cycles due the wasted spark Mazda design rather than having one separate lead coil for each rotor like the trailing coils. IMO, I would buy a new lead coil at least. I bought all three new to be safe. Beats a engine rebuild hands down.
Mike

NGK is not the stock wire, Yazaki's are.

I think the Yazaki's were just on them from the factory, I've NEVER seen them for sale. The NGK's are OEM quality and are resold by Mazda. Color coded and labeled. And like $25 for a set.

Dale

have you ever looked? we used to stock them

the NGK's are fine, they are just not Original Equipment Manufacturer

I looked around yesterday and just now, if they are available they aren't easy to get.

Dale

exactly! the Yazaki's are date coded too, so you really need to bleach your white gloves!

i'm just correcting a really minor point, if you want the extreme example we put Penske shocks on the miata last weekend, they came from Mazda boxes, but that does not mean miatae were built with Penske shocks

It does make you wonder what the story is behind YAZAKI being used in production line and NGK being sold by MAZDA as replacements.

Yazaki makes the wiring harness, in fact they are one of the largest harness makers in the world (its kind of faci-boring, but they make the harness and the wire, but are using the AMP/Tyco/Sumitomo connectors, complex)

i think Mazda USA just supplies NGK by default, and there is nothing wrong with this, NGK stuff is good, and its easy to get and its cheap. i'm sure if we looked we could find other examples of this kind of thing in other brands. wheels are another area where Mazda does this, the newer cars have different wheel vendors, with different part numbers, but often they get superseded to just one number.

i could go on, this kind of thing is my day job...