Misfire at 4k ish. Not ignition?
 

Hi Guys,

Like many people here, I have a CEL on for a Misfire on the rear rotor. Since I have owned the car, it has been this way. If I keep it under 4000 rpm's, it won't misfire, but once I rev it up past that area, it begins to happen. It revs up great and drives perfect, but I can't seem to get the misfire to go away.

I don't ever have a misfire on the front rotor, and I have swapped the coils, the plugs, and the wires from front to rear to see if the misfire would move. Sadly, it did not.

If the misfire Had moved when I did this, I would have happily bought new coils, plugs and wires, but since it didn't make any difference, I feel like that will not fix my problem.

I have searched this to death. Does anybody have any thoughts on what happens at 4k rpm that could cause a misfire (other than ignition)?

P.S. Its a 2005 Rx8 6 speed with 35K miles.

Thank you!
-Jeremy

Couple questions for you. First, are you certain that you're experiencing a misfire? Are you hearing noises or experiencing a power loss of any kind? Our knock sensor is pretty crappy and can often report a misfire when one doesn't actually happen.

Only thing I can think would happen in that range is the secondary fuel injectors open. If there's an issue with the injectors it *might* produce a lean condition.

Are you using 91 or higher octane fuel? Tried the throttle body coolant bypass?

Well, the only CEL code I ever get is for the rear rotor misfire. I cannot feel or hear a misfire at all, and the performance of the car is great. Is there an easy way to test for "phantom knock" (That's what us Mitsubishi guys call it ;) )

We actually have only used 93 octane in it, but we have only owned the car for about 2 months.

My throttle body is set up just like it came from the factory, no bypass. Also, the car is 100% stock other than the K&N air filter.

What else you got? :)

-Jeremy

I'm curious if you might have a faulty knock sensor. If you're using 93 octane then you should be in good shape since you're stock. Phoenix has piss water 91 octane and I've ran some aggressive tunes without too much trouble.

If you're running 93 then you're probably not in need of the coolant bypass.

I'm rather stumped regarding this with the exception that your knock sensor might be faulty. You can hear detonation through the motor most of the time. It's a pretty awful sound and while you might not know at the time what it is, you'd notice it.

I take it that you had the problem prior to the K&N airfilter being installed? If not, you might try cleaning your Mass Airflow sensor. I'd suggest that from time to time anyway cause the oil in the K&N can sometimes coat the sensor.

If you're still under warranty I'd have them take a look at the misfire issue and look at the knock sensor.

I have heard knock on turbocharged 4 stroke engines but have never heard it on a rotary. I would like to keep it that way :) I know that I do have a slightly noisy idler pulley on the front of the engine, I wonder if that is bad enough at high rpm to piss off the knock sensor.

I have cleaned the MAF, and sadly that didn't make a difference either.

It is not under warranty, so that is out of the question too.

I think I may start with the noisy pulley and check to see if the motor mount is damaged. I have heard that these engines eat mounts, so it is worth checking I suppose.

Thank you, and if anybody else has any thoughts, please feel free to share.

-Jeremy

Checking the motor mount is a good idea. I've experienced a blown mount without too much effort. Mazda did redesign them and they are not to hard to change on your own.