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Misfires can be caused by many problems in different areas of the car. Some are an easy fix with little to no cost, and others are major, such as loss of compression in one/multiple rotors. This is a list of possible problems and solutions that you can carry out in order to diagnose and possibly fix your misfire. I want to note that these are in no particular order, and that each person's circumstances can vary. Therefore I encourage reading over all the possibilites and going from there.
This includes coils, plugs, and/or wires. There are 12 components total, and even 1 becoming weak can cause misfires.
The coils on the RX8 have long been known to cause problems and misfires in these cars. With an average lifespan of approximately 30,000 miles, the plugs should be changed on a regular basis. The coils as well will need changing, possibly around the same time. If you change the coils, always change the plugs as well. The wires too can have issues with them, as well as the harness's that connect to the back of each coil assembly.
Solution: New Coils, Plugs, Wires
There are many different types of replacements you can obtain to fix the burnt out coil/plug issue. See Maintaining Your RX-8: Ignition Health for purchase options you have
To check the plugs, take them out and look at them. Brown is OK, but black and chunky is BAD. If you can take out the plugs, you can tell if there OK or not.
Check the coils by attaching an inductive timing light to the wires and revving up the engine. If the light blinks faster and faster (Or intensifies), then the coils should be in OK working condition. You can also use a spark tester (Looks like a spark plug with a clamp) to test the spark for color, intensity, and stability.
Also check over the wires with an inductive timing light, as well as visual inspection. You should also be able to tell when you connect the wires on both the coils and plugs that they seat properly when the snap into place. The harness's on the back of the coil packs should also be checked; it may not be likely that these are damaged, but if you find that with an inductive timing light, one coil is not producing spark throughout the rpm range, it could be coil, wire, harness.
Any time you disconnect the plugs wires from either coils or plugs, double check your work to ensure that you reconnect them properly! This image is very useful to easily see exactly which coil powers which spark plug, and how the wires trace between them.
It is not uncommon for the MAF sensor to become dirty inside the intake. Although this may not be the current issue directly related to the misfire, it can play a significant role. The MAF sensor is for Mass Air Flow measuring, which in short helps with your air/fuel ratio.
Solution: Clean or Replace
For the most part, you will most likely be able to clean your MAF sensor. There is a link included with more detailed instruction, but in short, remove the MAF sensor from the intake and spray the two prongs inside of the cylinder with Electrical Contact Cleaner. Be careful to not touch the sensor with your hands, either. Note that replacing the sensor may be necessary if it is damaged.
RX8Club.com: DIY: How to clean the MAF
A dirty ESS (E-shaft) can cause a misfire as well, which is related with NVRAM (Non Volatile Random Access Memory).
Solution: Clean ESS, Reset NVRAM
Also known as the “20 Brake Stomp”, this is an easy, quick, and free fix. Simply turn the car to On mode, and stomp the brake pedal 20 times within 8 seconds. If successful, the oil pressure gauge will sweep. Please Note: You must have the up-to-date ECU flash. Although older flashes do support this procedure, only the updated flashes (past few) will give the oil pressure gauge sweep confirmation.
RX8Club.com: tired of searching ess cleaning
The fuel pump is an obvious problem that can be directly related to a misfire. Although not too common for the fuel pumps to go, it has happened to many people. To check if the fuel pump is in working order, hook up the fuel line to a pressure gauge. If the pressure is Around 58 PSI, then you should be fine in this area.
Solution: Replace Fuel Pump
Title states it all - Replace the fuel pump. If the fuel pump is one of the problems, or the main one for that matter, get it replaced ASAP.
The fuel pump’s harness can also be an issue. Whether damaged, corroded or completely destroyed for some reason, it will cause the fuel pump to not act properly or at all, therefore causing a misfire. Check is the same way as the fuel pump - If the pressure is off, you may be able to check the harness for proper connectivity by either just observing it or trying some sort of grounded light method on it.
Solution: Replace / Fix
If the wires are broken and you want to try it, solder the wires up. But I would highly recommend replacing the harness.
Yupp, that’s right. Low fuel can cause fuel pump issues, which can cause a misfire. (And its not good to run your car on low fuel because it makes the job on the fuel pump significantly harder).
Solution: Fill Up
Fill up on gas
Many people will one day suffer from a bad or clogged Catalytic Converter (AKA 'Cat'). This is very easy to test out - On a night, and on a safe road, take your car for a hard drive. After that, look underneath your car and see if the Cat is glowing. If it is, its clogged. Also, you may notice a loss in power or acceleration.
If this does not work, the best way to inspect the Cat is to physically remove it and hold it towards the sun / point a flashlight into it.
Solution: Gut or Replace
If you are still under warranty, you can most likely get your Catalytic Converter replaced at no cost to you. If, like myself, you are not under warranty, you have two options: Gut the Cat, or Replace the Cat. To gut it, remove the Cat (Search in DIY), and gut it by pounding out everything inside of it.
Caution: Make sure you do not hit the O2 sensor!!!
Caution: Make sure the cat is actually dead before you willingly destroy a $1,300 cat! Plenty of people would be happy to trade you their dead cat for your good one.
If you do not want to gut the Cat due to emissions, noise, or apparent smell, then either buy a Mazda OEM one ($1,300+) and get it installed, or, replace it will a higher quality Midpipe, Resonater, High-Flow Cat, etc. You can find these from Racing Beat and other companies, although I would highly recommend the BHR Midpipe.
Low compression is a for-sure for misfires. If you have low compression, you will get a misfire. But in all honestly, if you have low compression, a misfire should be the least of your concerns. To check your compression, take it to a dealership. It should only cost half/1 hour of labour at most, and will give you accurate results. Because of the fact that these are Rotary engines, you cannot get accurate results from a normal compression tester, as you have to check each face of each rotor for its separate values - In other words, get it done properly.
Solution: Repair, Rebuilt, Replace
Well, if you have lost compression, you have three (3) options: Sell the car, do/get an engine rebuild, or get a whole engine altogether. If you are still under warranty, time to visit the dealership for a new engine! Otherwise you don't have many options:
The above prices are all just for the engine. Shipping, installation labor, and possible core charge would all be extra, but those will be incredibly variable depending on where you live, how much you can do yourself, etc...
There are many preventative measures one can take to help, well, prevent misfires from occurring. Such idea's could include: Installing a catch can, replacing the coils and plugs when necessary, get a compression test once every year or so, reset your NVRAM or KAM when the car is running roughly, keeping a close eye on your CAT, etc.