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My 2004 RX-8 is misfiring and getting TERRIBLE gas mileage.

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Old 03-10-2013, 10:05 PM
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My 2004 RX-8 is misfiring and getting TERRIBLE gas mileage.

Well, guys. It's been nice.. That's for sure. My car currently has around 88k miles on it and just started to have multiple misfires not too long ago. Every time I floor it it'll LAGS like a beech. I swear, if my 0-60 times aren't above 10 seconds I'd shat my pants. Yesterday I got OWNED by a prius. AN EFFING PRIUS GUYS! There are times I feel like the car has extraordinary power, then there are times where I'm pressing it to the floor and it feels like I have an old man pushing on the back. That's until I feed that old bag o sheet some redbull. After it hits 5k it hulls ***. But then when I get up to 7k the check engine light starts blinking. I get such bad gas mileage I'm at the pump every 40 miles..

I'm going to take a wild guess and say my Coils, Plugs & leads need to be switched out or else my catalytic converter will go bad.


Engine code P0300

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Old 03-10-2013, 10:57 PM
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Charles Bundy
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P0300 IS a misfire. Suffering a misfire? START HERE. Don't lolly-gag too long!
Old 03-10-2013, 11:03 PM
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You will typically have at least 1 of the 12 parts (4 coils, 4 plugs, 4 wires) fail within 30,000 miles. Replacing them is regular maintenance. Failing to replace them is a severe cascading failure situation, where additional ignition components start failing faster because of the first failed one. The cat clogs very quickly ($1,300), O2 sensors get damaged ($230 and $130), and engine damage starts($thousands).

Even a cat that DOES NOT have active flashing CEL (which is always a misfire!) but fading ignition components can be down around 30whp. The change is pretty dramatic.

Driving around with misfires severe enough to actually flash the CEL at you is well into the range where you start starting to damage other stuff.


Ignition isn't the only reason for misfires though, so if it's still doing it once you have replaced the ignition, make sure you check over that misfire thread.
Old 03-10-2013, 11:09 PM
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Originally Posted by iSki123
My car currently has around 88k miles on it and just started to have multiple misfires not too long ago. Every time I floor it it'll LAGS like a beech. I swear, if my 0-60 times aren't above 10 seconds I'd shat my pants. Yesterday I got OWNED by a prius. AN EFFING PRIUS GUYS!
You're the kid who works at the ski lodge, who paid cash for their RX-8, who had their "friends from High School" key the crap out of it, and yet here you are, knowing you're getting multiple misfires, and yet you keep driving the car in this condition, complaining that they can't keep up with a Prius from a stop. And to top off all of that, you know your insurance agent is ripping you off, yet you do nothing about it, no matter how much advise we give you.

*Sigh*

BC.
Old 03-11-2013, 01:38 AM
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Originally Posted by Bladecutter
You're the kid who works at the ski lodge, who paid cash for their RX-8, who had their "friends from High School" key the crap out of it, and yet here you are, knowing you're getting multiple misfires, and yet you keep driving the car in this condition, complaining that they can't keep up with a Prius from a stop. And to top off all of that, you know your insurance agent is ripping you off, yet you do nothing about it, no matter how much advise we give you.

*Sigh*

BC.
...THIS.

(and complains about it as though it's the car's fault).
Old 03-11-2013, 08:47 AM
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and i got warning for stating the obvious(read: pissing the **** out of)

now im just gonna sit back, relax, and enjoy watching these omg mpg thread popping everywhere
Old 03-11-2013, 10:34 AM
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Originally Posted by Bladecutter
You're the kid who works at the ski lodge, who paid cash for their RX-8, who had their "friends from High School" key the crap out of it, and yet here you are, knowing you're getting multiple misfires, and yet you keep driving the car in this condition, complaining that they can't keep up with a Prius from a stop. And to top off all of that, you know your insurance agent is ripping you off, yet you do nothing about it, no matter how much advise we give you.

*Sigh*

BC.
I just noticed the misfiring, I stopped driving it. The diagnostic codes kept wiping their self off the engine computer. Therefor there was no way to actually know if it was truly "misfiring". As far as my insurance agent, I realized I got a 6 month plan. So I'm locked into paying the jackass 6 months straight or else I'll get charged some sort of fees. As far as the key marks, I got them repaired.

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Old 03-11-2013, 10:43 AM
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flashing meaning misfire.
can be as small as needing new plugs to engine replacement.
Old 03-11-2013, 11:04 AM
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Originally Posted by iSki123
I just noticed the misfiring, I stopped driving it. The diagnostic codes kept wiping their self off the engine computer. Therefor there was no way to actually know if it was truly "misfiring"
The ECU keeps track of misfires in a table. They can be read with a halfway decent OBD2 reader.
Old 03-11-2013, 01:32 PM
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Originally Posted by jasonrxeight
flashing meaning misfire.
can be as small as needing new plugs to engine replacement.
It only flashes every now & then, it's not constant. Engines internals are healthy overall, I haven't done a compression test yet though. I will after I find replace the suspected problem parts...

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Old 03-11-2013, 01:36 PM
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Originally Posted by iSki123
It only flashes every now & then, it's not constant. Engines internals are healthy overall, I haven't done a compression test yet though. I will after I find replace the suspected problem parts...

- iSki123
"I'm having some health symptoms, I haven't been to a doctor but I'm sure I'm in perfect health...".
Old 03-11-2013, 01:36 PM
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i was thinking the same exact thing .... i'm quite interested in what 'internals' he is referencing too lol.
Old 03-11-2013, 03:20 PM
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Originally Posted by iSki123
It only flashes every now & then, it's not constant. Engines internals are healthy overall, I haven't done a compression test yet though. I will after I find replace the suspected problem parts...

- iSki123
A compression test is the only reasonable method you have of determining the health of your engine internals (read: the seals). If you haven't done a compression check, you have no idea what the health of your engine is.

Guessing that you have a healthy engine or convincing yourself that it's healthy is somewhat inconclusive.
Old 03-12-2013, 02:26 PM
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Installed new coils, sparks and leads. Drove it two miles and the dang thing started to rattle on me, LITERALLY. It shakes violently and sounds like a spark plug hole is open. It's louder than F and it stalls. I had to push it two miles home.. I have no clue what to do. I checked the sparks, coils & leads and everything seems to be fine... I think this is the end guys. =[
Old 03-12-2013, 02:32 PM
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Are you sure that you installed the wires in the correct order? If you crossed them and it's firing the wrong plugs at the wrong time, it could easily do this.

Of course, if that is the case, then it could have also damaged the engine. For example, firing the rotor 1 leading plug when the rotor 2 leading plug should be getting fired, you will be igniting 2 rotors at once (roughly). Can lead to all sorts of problems, shakes, bangs, etc...
Old 03-12-2013, 02:36 PM
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Originally Posted by RIWWP
Are you sure that you installed the wires in the correct order? If you crossed them and it's firing the wrong plugs at the wrong time, it could easily do this.

Of course, if that is the case, then it could have also damaged the engine. For example, firing the rotor 1 leading plug when the rotor 2 leading plug should be getting fired, you will be igniting 2 rotors at once (roughly). Can lead to all sorts of problems, shakes, bangs, etc...
It was running and driving perfectly, I said how nicely is sounded and I was pretty much AMAZED. Then it starts making these bogging noise when I rev it up like this:


It's as if it's not firing, the thing is. It was running beautiful until I started to actually drive it. There were times where it sounded and ran normal when I was driving it.. But then this LOUD noise appeared.. How could this be possible with new coils and leads?
Old 03-12-2013, 02:46 PM
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I'm going to take a couple of quick guesses here.

1: My Catalytic converter is clogged due to the misfiring before.

2: Side seals & Apex seals are a loss.

3: Coil blew instantly when I installed them.

4: Engine is a total loss.
Old 03-12-2013, 02:46 PM
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Did you plug the MAF back in after you installed the coils? No MAF plugged in will bog crazy hard.

What I mean to get across is don't jump to "dead engine", when it could have been a mistake during the replacement that just needs to be fixed. Work through the steps first.
Old 03-12-2013, 02:48 PM
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Significant vibration at or near idle, idle like a lawnmower, and sudden loss of half the engine's power output are signs of broken apex seals and complete loss of compression on one rotor/chamber.

Do the poor man's compression test by ear, or use a piston tester if you have one.

compression test. (for the rx8 you can just unplug the crank angle sensor under the main pulley during the test).

Last edited by RotaryResurrection; 03-12-2013 at 02:52 PM.
Old 03-12-2013, 02:56 PM
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Originally Posted by RIWWP
Did you plug the MAF back in after you installed the coils? No MAF plugged in will bog crazy hard.

What I mean to get across is don't jump to "dead engine", when it could have been a mistake during the replacement that just needs to be fixed. Work through the steps first.
MAF was plugged back in, that's the last thing I connected before I started the motor. I'm not throwing any codes or check engine lights. Which KILLS me...
Old 03-12-2013, 05:08 PM
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Just did a compression test, it's reading about 100PSI or more ALL AROUND. Spark plugs were terribly loose though. You think that's what caused my issue?
Old 03-12-2013, 05:09 PM
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Could be. Blasting the combustion out past the plugs, misfiring from the plugs not getting solid grounding to the housing, etc...

Secure them down properly and take it for a drive.


Problems immediately after doing work on a car are nearly always due to what you just did, usually a mistake made.
Old 03-12-2013, 05:51 PM
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You wouldn't believe what the **** just happened, it started spilling oil EVERYWHERE. I started it up and BOOM oil leaking in every which way..... If it couldn't get ANY worse.. I don't think this is related to the hard starting and terrible running. Because it leaked an assload of it... It seems to be leaking from the starter area...

Last edited by iSki123; 03-12-2013 at 05:56 PM.
Old 03-12-2013, 06:12 PM
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Is the "boom" an actual representation of a sound you heard? or just emphasis on it being sudden?

What were you doing with the car when it happened, was it under motion? what revs? etc...

Oil leaks are usually viable from:
- Front oil cooler lines that rust through
- Rear main seal inside the transmission bellhousing (rarely a significant leak)
- oil filter not secured properly
- Cracked engine block
Old 03-12-2013, 06:49 PM
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Originally Posted by RIWWP
Is the "boom" an actual representation of a sound you heard? or just emphasis on it being sudden?

What were you doing with the car when it happened, was it under motion? what revs? etc...

Oil leaks are usually viable from:
- Front oil cooler lines that rust through
- Rear main seal inside the transmission bellhousing (rarely a significant leak)
- oil filter not secured properly
- Cracked engine block
That's just me trying to explain how it came out of nowhere, it just started to leak oil like a beech. I should probably take it to the stealership or a mechanic. I don't understand how the engine could have 100PSI all around the board & a good ignition system and sound like a tank. Although, this could've been a issue that I never noticed. How the hell could this all happen in one day... My brother was just under the car.. He told me how he found a hole right before the catalytic converter that's rusted out in the exhaust... I guess I needed a new exhaust system.

I bought the RX8 from HELL...

Last edited by iSki123; 03-12-2013 at 06:53 PM.


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