I started my RX8 today after work and it ran VERY rough for about 30 seconds and then straightened up. On the way home I hit 9k RPMs in 2nd and when I hit 3rd gear at about 7k RPMs it started to misfire again....badly. Now when I hit high RPMs it misfires. I have already ordered new coils. The car has about 94k on it and it has a brand new motor with about 3k on it. it has new plugs and plug wires already. It did not smoke at all when it misfired badly ( it did when my old motor blew. ) Should the coils fix my problem?

 

Usually, yes, new coils will fix high rpm misfires. Though it's possible it's your wires and/or plugs as well. It's typical for dealers to reuse the old ones on a reman install.

 

I asked specifically and the tech told me he put new plugs in. would coils make it run rough upon starting in 50 degree weather?

 

Not quite the right way to think about it.

In order for an engine to create the needed combustions to start or run, everything has to be working right.

The battery or alternator has to be providing enough voltage to the coils, the coils have to be converting that voltage and current appropriately, the wires have to be letting the current reach the plugs without resistance, the plugs have to be getting that current to the tip, the current has to bridge the gap successfully without fouling, and the current has to return to the battery or alternator. And this is just the ignition.

Then you have the fuel system with fuel present, voltage to the fuel pump, fuel pump generating pressure, injectors getting the needed voltage to cycle, injectors opening and closing correctly at the correct times, and nothing fouling the fuel itself.

And then there the compression of the engine. A squick spritz of fuel in mid air that is ignited generates no pressure against anything. Done inside the engine, all the seals need to be sealing correctly so that pressure is transformed into usable force to generate the work. In order for that to work correctly, the charge has to be compressed beyond a certain point before being ignited.


And there are still more components, like the various fuses, the e-shaft position sensor to tell everything WHEN to fire/fire, etc...


See everything that can go wrong?


Issues with misfires, power loss, starting, etc... is never a matter of "this part should fix my problem" but always a matter of "where is the link in the chain failing or broken". And you have to eliminate parts that are known to be working correctly to get to that point.

So back to your issue, the tech just "Said" he put new ones in. Are you sure? Did you get charged for it? If not, did the warranty get charged for it? It should be on the invoice because it's not automatically included. Pull a spark plug (easy to do, right inside the driver's side wheel well) and check the tip. 3,000 mile spark plugs will look radically different than 30k+ plugs, or whatever you had before. That still doesn't address the plug wires. If this started all of the sudden, perhaps a plug wire is jostled loose, jumping around on the plug. That's a free and easy fix.


To really answer your questions better, we need you to be much more specific in what is happening when. Not just what isn't happening, but what is happening correctly. Nearly every common problem in the 8 shares at least 1 symptom with another common problem. Half of the common problems all have almost the exact same symptoms!

 

I didn't check the plug wire...I probably should though....and yes the spark plug set is in the Mazda invoice. I'll check before I pay for the coils...any other suggestions?

 

Just checked the plug wires and everything is as tight a can be. And it didn't start rough when I started it. Should I still get the coils or no? The dealer mentioned that I could have a coil breaking up, but I just attributed it to then trying to get more with out of me. I just don't want to spend 126 dollars on coils if I don't have to...

 

If you don't want to buy 4, you can buy a $13 coil tester and test each of the coils to find which one is not firing cleanly, and just buy one to replace it.

 

Look at it as a preventive measure......if you plan to keep the car the other three could fail too. Do you want to do this whole thing again...... for that amount of money.

 

Failing coils will cause your Catalytic Converter to fail. That's about a $1200 hit by it's self.

Pay me now. Pay me more later.