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Engine Misfire at High Speeds

Old 02-22-2009, 01:55 AM
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Engine Misfire at High Speeds

Hey guys, I need some advice with my RX8. It is misfiring when I put my foot down while driving at 80km/h or more. There is a flashing CEL that disappears after about 5 seconds.
2004 AT 48xxx kilometers
The spark plugs/coils were all changed last year and 6000km ago. I believe it was flooded once/twice by the previous owner since that time.

Should I be concerned about a more serious problem than coils/plugs?
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Old 02-22-2009, 01:58 AM
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chances are is that it could be your cat that is causing the problem, also did you read the code? If so what was it?
Oh other problem is that it's a 4speed.













Jking about the last one...
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Old 02-22-2009, 02:05 AM
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Might be an issue with the PCM...did you do both the PCM reset procedures after you had the plugs and coils swapped?
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Old 02-22-2009, 07:40 AM
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Better go get that code read....................given all you say, I'm going to guess plug wires...........they do go bad ya know. Also, check and make sure that all plug wires are on good on both ends. If you don't feel/hear them snap a little, then keep working with them until you do. Either that or the CAT, but I don't think that is it this time around.
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Old 02-22-2009, 10:13 AM
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It's common for rotories to misfire, especially the MT.


Make sure the wires are tight.

Clean the MAF......
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Old 02-22-2009, 11:00 AM
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thanks for the quick response guys.

Apparently the cat was causing problems earlier according to the dealer records. It is an aftermarket Greddy exhaust. The previous owner had it fixed by replacing the exhaust converter a year ago.
I should add the exhaust smells like pure gasoline everytime I cold-start it.


How do I check the other problems such as wire looseness? Haven't really gotten my hands dirty like this before but I'd like to give it a shot.

Last edited by igotacookie; 02-22-2009 at 12:16 PM.
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Old 02-22-2009, 12:20 PM
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I think the PCM should have learned in 6k km about the new plugs coils. Not sure what effect flooding might have had on the plugs, it could have fouled them.
I'd suspect the cat or a restriction in the exhaust (I just got my cat replaced for this reason.) Is the cat OEM, or does the Greddy include a cat? Parts inside the cat can break off and clog it. The flashing CEL was for engine misfire, but it won't stay lit and be readable until it happens on 2 consecutive drive cycles.
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Old 02-22-2009, 01:24 PM
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http://www.rx7.com/RPGReddyRX8exhaust/

this is the exhaust. Seems like it should still be the OEM cat converter.

So I can't get a Cel code unless the check engine light stays on? I thought it might have logged something everytime it goes off...
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Old 02-22-2009, 06:35 PM
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Originally Posted by igotacookie View Post
http://www.rx7.com/RPGReddyRX8exhaust/

this is the exhaust. Seems like it should still be the OEM cat converter.

So I can't get a Cel code unless the check engine light stays on? I thought it might have logged something everytime it goes off...
It should store any codes..................I'm pretty sure.
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Old 02-23-2009, 08:18 AM
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If the reader can read pending codes I guess it'll pick it up. I use a scangage, which can't read pending codes, but I guess the high-end readers can.
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Old 02-23-2009, 09:49 AM
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I would also check the Injectors,..or injectors wires,...maybe 1 injector is sticking and playing a game on you,...sometimes they get stuck open and flood or make your gas mileage go bad.
Maybe thats the extra fuel smell you are getting.
Good luck.
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Old 02-23-2009, 12:18 PM
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Originally Posted by igotacookie View Post
Hey guys, I need some advice with my RX8. It is misfiring when I put my foot down while driving at 80km/h or more. There is a flashing CEL that disappears after about 5 seconds.
2004 AT 48xxx kilometers
The spark plugs/coils were all changed last year and 6000km ago. I believe it was flooded once/twice by the previous owner since that time.

Should I be concerned about a more serious problem than coils/plugs?
Just curious, did the previous owner state that they were changed 6000 km ago or did he have records stating it?
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Old 02-23-2009, 06:50 PM
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i have the dealership records stating plugs/coils was changed at 42k (now 48k)

This car had a lot of issues in the past. The original cold air intake had to be taken off, as it was choking the engine. Replaced by Sunridge Mazda with a MS CAE.
Spark plugs changed twice in a 1.5 year period.
4 coils replaced about a year ago
Had a catalytic converter problem as well pulling a CEL about the O2 sensor. Seems like it was taken care of already at some muffler shop.
New Alternator belt + oil pan installed in December 2008, month before I bought it.
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Old 02-24-2009, 05:49 AM
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I would take it to a Mazda dealer and have them read the code they will also tell you whats wrong with your 8. Or if the wait is to great see if autozone can read it. Then corss ref the code to Zoom44 sticky about the list of codes. There you will find whats wrong with it.
-Gil
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Old 02-27-2009, 02:41 PM
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Update:

Started it this morning and CEL was on and solid. Throttle seemed limited, I could not rev and acceleration was extremely slow (to the point where I could not keep up with traffic). Limped the car to the Mazda dealership. Haven't heard back yet. The Exhaust looked hot! Like it was -20C outside and it looked like it was burning. I'm going to assume the cat died haha.

So questions about the CAT replacement. Its a 2004 vehicle with 49k (km). Will this be replaced under a recall/warranty? If the same issue arises again will it be replaced multiple times? Should there be anything I need to be wary of that can be attributed to this problem. Like can it damage the engine?

Thanks for any input
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Old 02-27-2009, 03:04 PM
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Cat. is fried. They have an 8yr 80K mile emissions warranty. It should be covered for free. It would not cause a blinking cel though so make sure they tell you what the CEL was for.

My other though was the e-shaft sensor got lost. a computer reset should take care of that though.
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Old 02-27-2009, 06:22 PM
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thanks for the help guys!

I created a new thread since it seems to be a different problem entirely.
https://www.rx8club.com/showthread.p...96#post2889196
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Old 02-28-2009, 11:12 AM
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Clogged cat will definitely cause a flashing CEL due to misfires.
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Old 03-01-2009, 03:48 AM
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What if you have no cat and you have the same issues? well when I had my AT it was my spark plugs that where bad. Turns out I was not the only one who had this issue.
Just keep that in mind.
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Old 03-01-2009, 01:00 PM
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Originally Posted by skrubol View Post
Clogged cat will definitely cause a flashing CEL due to misfires.
My point is the clogged cat. will not fix the misfire issue necessarily.
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Old 12-30-2010, 08:02 PM
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I have the same issues right now and I had straight pipe and now im back to the factory exhaust...I'm assuming my air filter could be horribly clogged up which I haven't changed yet, but i'm about to, along with cleaning my MAF, but something is telling me that I have a sticking injector..
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Old 12-30-2010, 08:11 PM
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First get the code read and take it from there. I also have an 04 and when my OEM cat converter went I did not get a CEL. Lucky me I was 2 miles away from the dealership since I could not even go 20 mph downhill.
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