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Old 12-03-2008, 11:21 PM   #1
newyorker
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CEL code P0304

copy and paste from another forum i already asked this on

Car: 2004 Mazdaspeed Miata 43k miles

Issue: (3)P0304

Tuesday
What happened:
OK so yesterday I am driving to work and all of a sudden I notice a CEL on. Go after work and get it checked, car comes back with (2)P0304 code. For those who don't want to look them up

P0304 - Cylinder 4 misfire


Car's behavior:
Misfires only occur at idle (800rpm), behaves normally under load. Misfires are totally random, there could be 5 in a row within 5 seconds, or sometimes there will be one, then 10 seconds fine, then 1 more..sometimes 3 more...etc.etc. Cleared the codes and thought it was just random.

Wednesday
What happened:
Driving to school today, stopped at a light for a little while, CEL comes back on. Come to Advance Auto after class to get the code(s) ran, comes back with (1)P0304, same cylinder 4 misfire.

Car's behavior:
Misfires only occur at idle (800rpm), behaves normally under load. Misfires are totally random, there could be 5 in a row within 5 seconds, or sometimes there will be one, then 10 seconds fine, then 1 more..sometimes 3 more...etc.etc. Also noticed that if I sit at a light and hold the RPM at ~1,500 or so, I can feel it misfiring very slightly and only through the shifter. If at idle the misfires are strong to the point where it feel like someone keeps tapping you in the back bumper.

Solutions?
All of this leads me to believe I have a bad coil pack on cylinder 4. I think that if the spark plug was at fault the misfires would have been more consistent and drivability would be affected. Furthermore, a search on Miata.net revealed quite a few similar issues with misfires caused by coil packs. It seems like it has something to do with the voltage going to the coil pack that makes it act weird.


What should I do about this mess?



Today
Inspected plugs and they seem to be fine. Swapped coil packs from cylinders 2 and 4 around and cleared CEL. Waiting for it to come back so I can scan because misfire is still here. If it moves to cylinder 2, then I got a bad coilpack, if it stays at 4, I might have a bad plug that I can't figure out, or a clogged injector? But here is a twist.

The code reads a misfire in #4 but if if was a coilpack then it would also misfire on cylinder 1. The system has 2 coils, one mounted on cylinder 2 and one on 4. Cylinder 4 has a wire and plug that branches out to cylinder 1, and 2 has one that branches to cylinder 3. Wouldnt cylinder 1 misfire with cylinder 4 if the coilpack was bad?

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Last edited by newyorker : 12-03-2008 at 11:35 PM.
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Old 12-04-2008, 04:45 AM   #2
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Personally from what I've read it sounds like bad gas (Not the right octane level or just a crappy mix) or a plugged injector. However, I'm not saying it is absolutely not spark. But from what I've worked on, it's been more commonly (Unfortunately) fuel. But, IMO, I change my plugs/wires every 20K, coils every 50K, and injectors every 60K. It's probably not needed, but it's just what I lik to do just to make sure everything still works as good and efficient as possible. With that said, I think with a car like yours (Mazdaspeed edition) you should probably go ahead and replace everything (Minus the coils) since it's a guarantee that the problem will be fixed, and you know it's burning/squirting as good as new. Just my
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Old 12-04-2008, 08:05 PM   #3
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Quote:
Originally Posted by Satty101
Personally from what I've read it sounds like bad gas (Not the right octane level or just a crappy mix) or a plugged injector. However, I'm not saying it is absolutely not spark. But from what I've worked on, it's been more commonly (Unfortunately) fuel. But, IMO, I change my plugs/wires every 20K, coils every 50K, and injectors every 60K. It's probably not needed, but it's just what I lik to do just to make sure everything still works as good and efficient as possible. With that said, I think with a car like yours (Mazdaspeed edition) you should probably go ahead and replace everything (Minus the coils) since it's a guarantee that the problem will be fixed, and you know it's burning/squirting as good as new. Just my
I always use 93 octane but I am going to try some octane booster because it is possible that injector 4 is clogged or dirty. Parts aren't cheap to just start replacing stuff, coils are 130 each, wires are 70 each, so thats 400 just to replace the ignition stuff, then new plugs are 8 a piece, and injectors are I don't even want to know how much since I would have to use the stock 265cc injectors if I didn't want to re-tune for which I would need a standalone which is another 1200. I thought it was bad gas as well but it's kinda weird that it keeps missing on just the one cylinder. Im going to the meet tonight, so I'll see if the misfire moved with the coil but if I do have to replace coils and wires it puts a big stop on my plans for brakes and rollbar.
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Old 12-04-2008, 09:24 PM   #4
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Quote:
Originally Posted by newyorker
I always use 93 octane but I am going to try some octane booster because it is possible that injector 4 is clogged or dirty. Parts aren't cheap to just start replacing stuff, coils are 130 each, wires are 70 each, so thats 400 just to replace the ignition stuff, then new plugs are 8 a piece, and injectors are I don't even want to know how much since I would have to use the stock 265cc injectors if I didn't want to re-tune for which I would need a standalone which is another 1200. I thought it was bad gas as well but it's kinda weird that it keeps missing on just the one cylinder. Im going to the meet tonight, so I'll see if the misfire moved with the coil but if I do have to replace coils and wires it puts a big stop on my plans for brakes and rollbar.


I hear ya. Last time I did the Camaro, the plugs were 8 bucks (plus shipping), the wires were 142.90 (plus shipping), and the coils were 800 (bucks plus shipping). That's roughly 1050 for the general tune up job. lol. But, it's worth it IMO. Simply because I want no chance of have an ignition issue, since the SS will soon be running on juice. And tuning the fuel system isn't that hard...err, atleast not on my car. I have no idea about a Miata. But, remember. If you need to replace a coil, you are MUCH BETTER OFF doing your plugs and wires at the same time.
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Old 12-04-2008, 10:07 PM   #5
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Quote:
Originally Posted by Satty101
I hear ya. Last time I did the Camaro, the plugs were 8 bucks (plus shipping), the wires were 142.90 (plus shipping), and the coils were 800 (bucks plus shipping). That's roughly 1050 for the general tune up job. lol. But, it's worth it IMO. Simply because I want no chance of have an ignition issue, since the SS will soon be running on juice. And tuning the fuel system isn't that hard...err, atleast not on my car. I have no idea about a Miata. But, remember. If you need to replace a coil, you are MUCH BETTER OFF doing your plugs and wires at the same time.
If I have to replace one coil Ill definately do coils and wires at the same time but until I really know its a bad coil or wire or something, I don't see a need to throw 400 worth of parts into the motor if it doesn't need it...Im hoping its just a fouled up plug or something, but I'm really not sure at this point...just hope the CEL comes back by tonight.

If it were low octane gas wouldnt I throw a different CEL, like something regarding the knock sensor?
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Old 12-05-2008, 12:36 AM   #6
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Quote:
Originally Posted by newyorker
If I have to replace one coil Ill definately do coils and wires at the same time but until I really know its a bad coil or wire or something, I don't see a need to throw 400 worth of parts into the motor if it doesn't need it...Im hoping its just a fouled up plug or something, but I'm really not sure at this point...just hope the CEL comes back by tonight.

If it were low octane gas wouldnt I throw a different CEL, like something regarding the knock sensor?



Not exactly. MOST cars will usually throw a misfire code when there's bad gas in it. As you know I'm sure, bad gas won't combust properly causing a misfire in the cylinder. However, Thinking about it a little bit more, bad gas would cause a misfire in more than one cylinder, and it would be a random misfire. Also, did the CEL flash at all? If not, you're most likely looking at a cheap fix such as a fouled plug. If it did flash, you're looking at a little more money. Coil(s), wires, or worst case scenario, coil modulater (I doubt thats the correct name for it, but my memory hates me ATM. lol.
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Old 12-05-2008, 02:16 AM   #7
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Quote:
Originally Posted by Satty101
Not exactly. MOST cars will usually throw a misfire code when there's bad gas in it. As you know I'm sure, bad gas won't combust properly causing a misfire in the cylinder. However, Thinking about it a little bit more, bad gas would cause a misfire in more than one cylinder, and it would be a random misfire. Also, did the CEL flash at all? If not, you're most likely looking at a cheap fix such as a fouled plug. If it did flash, you're looking at a little more money. Coil(s), wires, or worst case scenario, coil modulater (I doubt thats the correct name for it, but my memory hates me ATM. lol.
It does not flash at all, just lights up and stays on. I picked up NGK Iridium IX plugs today, as well as some Lucas fuel injector cleaner just becasue my buddy said it's a good idea to use every 5k miles or so to keep things clean. Will scan code tonight, hoping that it's still in cylinder 4 so I can put in the new plugs tomorrow and be done with this whole mess.
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Old 12-05-2008, 04:30 AM   #8
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Quote:
Originally Posted by newyorker
It does not flash at all, just lights up and stays on. I picked up NGK Iridium IX plugs today, as well as some Lucas fuel injector cleaner just becasue my buddy said it's a good idea to use every 5k miles or so to keep things clean. Will scan code tonight, hoping that it's still in cylinder 4 so I can put in the new plugs tomorrow and be done with this whole mess.


If there's no more CEL there's no code to read. But I'll go with you in hoping new plugs and injector cleaner will fix it. Oh, and btw, Seafoam>Lucas. Also creates a hell of a smoke show.
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Old 12-05-2008, 07:18 AM   #9
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Now I got code P0302. Gonna do a resistance test on the packs tomorrow, and check them thoroughly. Also putting in the new NGK Iridium plugs tomorrow. I put in new gas and Lucas Injector cleaner and immediately the problem seems to have lessened but it's still there. Now that I think about it, someone told me a long time ago that they thought the car was misfiring at idle because they put their hand behind the exhaust and felt it kinda pop, so yea...just hoping this doesn't cost me too much.
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Old 12-05-2008, 10:15 AM   #10
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Quote:
Originally Posted by newyorker
Now I got code P0302. Gonna do a resistance test on the packs tomorrow, and check them thoroughly. Also putting in the new NGK Iridium plugs tomorrow. I put in new gas and Lucas Injector cleaner and immediately the problem seems to have lessened but it's still there. Now that I think about it, someone told me a long time ago that they thought the car was misfiring at idle because they put their hand behind the exhaust and felt it kinda pop, so yea...just hoping this doesn't cost me too much.


That would be a Cyl. 2 misfire correct? You're probably looking at a new coil. Easy fix...not cheap, but easy. I still would highly suggest doing all 4, but I don't know how strapped you are for cash. If you can't afford it, do the one. If you can, do em all.
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Old 12-05-2008, 10:33 AM   #11
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Quote:
Originally Posted by Satty101
That would be a Cyl. 2 misfire correct? You're probably looking at a new coil. Easy fix...not cheap, but easy. I still would highly suggest doing all 4, but I don't know how strapped you are for cash. If you can't afford it, do the one. If you can, do em all.
Yea, it's cylinder 2. My buddy said he can get parts at wholesale cost and got me a price for all 4 @ $198.75 vs. $400+ from the dealer so that helps a bit

Regardless, I am putting in the new plugs and I am pulling all the coils and wires for closer inspection and a resistance test, it might just be a bad boot or some dirt or something so they are getting taken apart tomorrow.
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Old 12-05-2008, 10:25 PM   #12
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Quote:
Originally Posted by newyorker
Yea, it's cylinder 2. My buddy said he can get parts at wholesale cost and got me a price for all 4 @ $198.75 vs. $400+ from the dealer so that helps a bit

Regardless, I am putting in the new plugs and I am pulling all the coils and wires for closer inspection and a resistance test, it might just be a bad boot or some dirt or something so they are getting taken apart tomorrow.


That all works. btw Id be happy with 400 for coils. Mine are 800 something.
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Old 12-06-2008, 08:53 AM   #13
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OK, after all of the worrying I think I finally fixed the issue. Took out the old plugs and thanks to a friend's advice, I took the gap down from .035 to .030 and it seems to have fixed the problem. It also seems to have made the car run much stronger, builds boost smoother, better idle, just makes the engine run so much better. Additionally, the plugs were gapped unevenly, anywhere from .035 to .037 on all 4 cylinders. Still going to install the new NGK plugs tomorrow, but I'm glad the car is running better, drove about 50 miles tonight for various meets and not a single misfire at a light whereas before it would miss anywhere from 1-10 times.

Will update.
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Old 12-06-2008, 10:12 AM   #14
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NICE! Spark plug gaps...HA. Never woulda thought of it...
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Old 12-06-2008, 04:28 PM   #15
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It idles smoother than my friend's 525i lol
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