Importance of 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.

  • Want more power?
  • Want better gas mileage?
  • Want a longer lasting engine?
  • Want a longer lasting catalytic converter?
  • Want a smoother idle?
  • Want a smoother top end?
  • Want to avoid a flashing CEL?
  • Want faster starts?
  • Want your sensors to last longer?

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 thread about the dyno test here: Impact of old coils, wires, and plugs

Do I have your attention now? Good.

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.

  • The excess fuel 'washes' the oil from the seals and housings, accelerating engine wear
  • The inefficient combustion will accelerate carbon buildup in the engine, around the seals, and on the plugs
  • The fouled plugs will further accelerate coil failure for both coils that spark in that housing
  • The carboned seals will stick more and more, wearing at uneven rates
  • The unburnt fuel and air are dumped into the exhaust, where they ignite rather uselessly
  • The blowtorch effect of post-engine combustion damages the O2 sensors and melts the cat elements
  • Fuel trims become more and more unstable as the O2 sensors are seeing the post-engine combustion more than they are seeing the engine exhaust itself, and they are being hammered by the blowtorching in the process
  • Once the cat clogs, this trapped post-engine combustion builds up increasingly greater heat levels, damaging the O@ sensors further, often making the cat heat shielding glow red
  • Eventually, the heat gets high enough that it lights the bottom of the car on fire. No, I'm not joking.

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

  • Power Loss
  • Gas mileage drop
  • unstable idle
  • bad idle
  • inability to idle
  • shaking at idle
  • unstable high rpm
  • misfiring
  • flashing CEL
  • coughing engine
  • glowing cat
  • flooding
  • inability to start
  • inability to pass an emissions sniffer test
  • and just about anything you can think of where a weak or missing spark causes problems

Why do coils fail so easily?

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.

Where can I buy new ignition coils?

You have a number of options for coils:

  • The Cheapest option: BWD/Intermotor coils from auto parts stores like Advance Auto, Pep Boys, Autozone. These ARE OEM coils, just being sold to auto parts stores directly from the original manufacturer. This is common for virtually every OEM part for any car older than about 5 years old. 4 coils, 4 plugs, and 4 wires can be had for around $190-220 total based on whatever promotion is running at the time, and usually shipped to your door for free. They are considered to be the first coil revision and you should expect to need to replace them around 20,000 miles, 30,000 miles max. They often come with a "lifetime warranty" by the auto parts store, which could potentially be leveraged for perpetually new coils. Advance Auto Parts online here: BWD/Intermotor Ignition Coil. The the top bar of the page for the current promotional offer.
  • The Best Upgrade: The BHR Ignition System upgrade can be had for $500 (shipping is free within the US), which eliminates the need to continue replacing coils periodically, as well as deliverying a significantly stronger spark for slight mileage and power gains. It is a proven kit with top notch customer service supporting it. BHR reports less than a 1% failure rate on their kit, and it's prized so highly that even used kits sell for about 80% of original retail. In many years of sale, no owner has reported reaching a lifespan limitation on the coils. It includes the wires, you still need to add plugs ($80). Purchase here: BHR Ignition System
  • The For-Sure OEM: Mazmart sells all 4 coils of the latest OEM coil revision (C) for $250, Supported by top notch customer service. They will likely last longer than 30,000 miles, but we don't have much solid data on how long the latest coil revision will last. If you are having trouble getting other coil options where you live, or are wary about purchasing coils from other sources, then this is your cheapest option for coils straight out of the Mazda dealer parts network. Mazmart also offers ignition sets, where you can purchase all 12 components together in one click. Purchase here: Mazmart: RX-8 Ignition
  • The Most Expensive option: Buying from a dealer will run you around $300+ for the coils, $500+ for coils, wires and plugs, and if you have them do the install, expect to get a bill for anywhere from $700 to $1,800. Yes, we see those numbers quoted all the time. You may not get the latest coil revision, and it is unlikely that the dealer or techs will be able to tell you what coil revision you have. Yes, you are getting shafted if you take this option, so bring lube.
  • The Highest Risk option: Ebay coils continue to pop up as counterfeit, mislabeled, dead on arrival, and have zero post-purchase support largely. They are the "cheapest" listed price, but when you add that $92 or whatever to the price of anything in the list above from having to do it over again, you can see that they are no longer the cheapest option. Do it right the first time. "Motor King" coils are popping up at an attractive price on Ebay, but are being proven as ineffective, to the point of being unable to get the engine fired most of the time. "Mazda" branded coils on ebay are almost always counterfeit. Check the seller's name though, since some legitimate vendors do sell coils there. The price will be $200+ though. Anything sold as "Mazda OEM" under ~$26 per coil should really be considered as suspect and probably counterfeit.

Spark Plugs

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:

  • RE9B-T (trailing / top plugs)
  • RE7C-L (leading / lower plugs)

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.

"LSx D585 Coil" Upgrades

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.