Misfire and po420 error code
 

I had received a po420 error code a month ago. I reset the CEL twice since then and it came back a few times, but now it's been off, and hasn't come back

The car seems to "stutter" (misfire) between 6000 and 7000 rpm under load, but then it picks up again when you get through the 7,000 rpm mark. I mostly feel it in second gear, but it's definitely present in all gears. (well, not 6th, since I'm not going that fast).

I replaced the spark plugs (which by the way, the old ones appeared very rich). I replaced then one by one, so the wires are on in the proper order - and tight. About 12 thousand miles ago, the coil packs were replaced, wires, and plugs due to a "not able to start" issue that we're all familiar with.

I have a hard time believing that the wires are bad in only 12,000 miles - I didn't think that it was the plugs, either.

I have a used set of coil packs that I bought from ebay a while back (they claim they're good) so I'm planning on swapping those in one by one to see if I can figure out if it's a coil pack problem.

Any suggestions on any other possibilities that could be causing this?

Also, are there any after market coil packs for this car that are more durable than the oem ones?

Thanks for your comments.

MazSport and Okada have Upgrades for the coil packs but expect to either wait a long time or pay a arm and a leg for the product.

wow, I checked okada - $735.00 - I hope it's for four, but that's way too much money.

Thanks, though

Mazsport is only $100 cheaper but it is a sweet product.

Or................................... https://www.rx8club.com/rx-8-parts-sale-wanted-44/fs-couple-oem-items-remain-138818/

Thanks, but I already have an extra set of oem - are the mazsport and okada's actually giving performance improvements? If the spark is igniting the fuel, completely, I always had a hard time believing that a "bigger" spark would do much of anything.
If they're more reliable, that might be worth the money, though.

How many miles on the air filter?

Take a timing light to each of your plug wires and verify that the coils are working, If your car continues to have misfires you will damage the catalytic converter which may be why you a getting a p0420 code.

Your cat is bad or you can check these:

Front H2O sensor is loose
Reset the Eccentric shaft.

Charles, how you tease us so.

air filter is a k&n and I just recently cleaned it.

I was thinking that the o2 sensor might be bad.

I'm not sure I understand how a mis-fire could "damage" the catalytic converter.

Resetting the eccentric shaft? Not sure what that is/how to do that. Is there a "how to" on that?

Thanks guys

eccentric shaft sensor that needs to be reset:

Unplug the neg. battery terminal for a few mins, then re-connect it and turn the car on to the acc position and tap the brakes 20 times quickly within 10 seconds to reset it. it will be succesfully done if you see the oil gauge sweep half way and back.

Misfires will allow unburned fuel to reach the cat which will damage the catalyist, once the cat is damaged it can no longer reduce emissions.

The PCM preforms a test on the cat everytime you drive the car and determines cat performance by monitering the front and rear o2 sensors. If the rear o2 sensor inversions match the front o2 inversions then the PCM determines the cat is no longer reducing emissions and you end up with a p0420 code.

Karl has spoken!

I believe the ecentric signal is in the KAM

Do this:
1) With the key in the off position, press and hold the odometer reset button and turn the key to on;
Continue to hold the odo button until the odometer reads "TEST" and then release.
2) Turn the key to off and repeat step one.

This will reset the entire PCM except the KAM which contains the sensor profiles amongst other things. You can reset it with the familiar procedure:

1) Turn the key to on
2) Depress the brake pedal rapidly 20 times in a row until the oil pressure gauge sweeps to halfway and back again.

Thanks for the explanations. This is what I'm planning to do. I have a used (but supposedly good) coil pack (for all of them). I'm going to replace all of them. If it's fixed, great. If not, the car had a new cat put in a while back - in NJ, cat's are warrantied for 80K miles (which hasn't expired yet) so I'm going to bring it in. Of course, I realize it could just be the o2 sensors, but I'll try the warranty route, first, and if they have to replace the o2 sensors, so be it.

Thanks.