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THIS IS PERHAPS ONE OF THE MOST IMPORTANT ARTICLES ON THE SITE. THE VAST MAJORITY OF PROBLEMS THAT THE RX-8 HAS TO DEAL WITH HAVE A DIRECT CONNECTION TO IGNITION HEALTH.
One of the most often overlooked or ignored parts of RX-8 ownership is the health of the ignition system. This includes the ignition coils, spark plug wires, and spark plugs. They fail. Often. So often as to be critical parts of regular maintenance.
The VERY FIRST answer to all of these is: Ignition. Nothing on the RX-8 will fail faster than the ignition, and nothing causes so much cascading damage like failing ignition
Before I detail about the ignition itself, I'll address that very first item from the list above. More power. One of the biggest complaints from enthusiasts is that the RX-8 doesn't have enough power. However, they ignore their ignition. A few years ago, there was a test to see exactly what impact ignition had on power. A stock RX-8 with 30,000 miles on the stock ignition and zero owner complaints was put on the dyno, and tuned. 172whp consistently after several runs. They then installed band new stock ignition, and retuned. 199whp consistently after several runs.
Let that sink in a minute. The owner had no problems with misfires or ignition problems. No complaints about power loss or gas mileage problems. But yet the weak ignition was already causing a 13.5% power loss! 27whp at peak. In a car where it costs $500-$1000 for the first 10whp gain, and $5,000+ for the next 20whp, it's moderately stupid to let $190 in parts cost you 27whp. See the RX8club.com thread about the dyno test here: RX8Club.com: Impact of old coils, wires, and plugs
Mazda officially lists the plug wires and plugs as part of regular maintenance, but not the coils. Many dealers STILL don't know how easily the coils can fail. And they fail about the same time as the wires and plugs, which is about every 30,000 miles. Some can last longer, some shorter, and it's more related to your total RPMs than it is to your mileage. Highway cruising is easier on the coils than spending a day pounding around a race track. It's also related to your spark plugs and wires, as carboned plugs or old wires will wear out the coils faster as well.
When our coils fail, they don't suddenly shut off. They start producing weaker pulses scattered among strong ones. The rate of weak pulses slowly increases and pulses start getting dropped entirely, which is where misfires start. All of this means that you aren't burning all the fuel and aren't using all the air that the engine pulled in for that combustion. And this is where the cascading failures start.
Driving with failing ignition, misfires, and/or a clogged cat is at best a lengthy repair bill. At worst, it could cost you your life, or that of friends or family riding with you.
Spark plug fouling and wire failure is largely the same result, since all 3 pieces are needed for a complete spark. Foul the plug and it doesn't matter if the coil and wire are good. Break down the wire and it doesn't matter if the coil and plug are good. Additionally, once any one of the 12 components fail, the other 11 will start failing faster and faster.
Symptoms of ignition failure include
This is largely because Mazda opted for cheap coils on the RX-8, after RX-7 owner complaints about how expensive their coils were. The RX-7 coils lasted much longer though. So Mazda went cheap, and we have to replace regularly. And you can't compare to piston engine coils. A piston engine with the same setup of 1 coil for 1 plug has an average RPM of about 2,500rpm and the coil is firing every other revolution, so the coil is firing about 1,250 pulses per minute. Our rotary has an average RPM of more like 4,000rpm, and each coil fires every revolution, so about 4,000 pulses per minute. That's a bit over 3 times more. Even a piston max RPM of about 6,000rpm vs our 9,000rpm makes the difference 3,000 pulses per minute vs 9,000 pulses per minute, or 3 times as fast.
If our coils would last about 3 times longer, you are talking an average of 90,000 miles.
You have a number of options for coils:
Always go with OEM plugs. The only reason to go with anything else is if you are turbocharged or supercharged, have researched ALL the options, and decide to go with something different. Even most FI setups use OEM plugs. OEM plugs are still the best plugs found for the RX-8. If you find something else you think would be better, it will also be more expensive. If it's cheaper than OEM, it's not better.
NGK Brand, two each of:
You can get them from most Mazda vendors, Amazon, and autoparts stores easily. The price range is $18-$20 for each plug typically, $72-$80 + shipping total.
Be wary of "LSx D585 coil upgrades", as not all D585 coils are created the same, and the standard generic D585 coil is not properly designed internally for the RX-8's ignition needs. They generally "work", but there are anomalies and performance issues that have to be solved, if they can be solved. They are almost always NOT a plug and play option, even if it is advertised as "plug and play". There is a lot more on the subject to understand, so it would be to your benefit if you learned about the needs prior to making a purchase.