Gen 1 misfire

Just bought a 2009 Speed3, it turned on check engine light on code is P0304 for misfire on cylinder 4 the car stutters at higher rpms above 3000 any idea where I should start? I’m a newbie

 

Lots of posts here.
1) swap plugs (not from Amazon, those are likely fakes)
2) swap the coil pack to another cylinder see if it goes to the other cylinder. If so bad coil pack. Oem only aftermarket is trash.


Still bad after?
1)Compression test. And leak down. You may need a motor.
2) take off intake manifold, pull injectors and replace the injector seals with Corksport seals as oem may be leaking.
3) clean the valves while inside.

 

Also, try some E-85 (gallon or so on a full tank) if you have it handy. Unlikely to help if your injector seals are bad, but may help if you just get shitty gas.

 

Sounds good guys thanks for the advice I will go this later today and hopefully it is just the spark plugs or coil packs... thank you!

 

Hey guys I switched the spark plug to cylinder 1 and the misfire moved with the spark plug so good news! Do you guys know what the gap is for the new spark plugs? Thank you in advance.

 

What spark plugs are currently in there and any idea how long you have had them. Might be time just change them out if they look like crap. Porcelain counts also, just not the electrode.
I usually ran mine at 0.028".
https://www.mazdaspeeds.org/index.php?threads/spark-plug-data-base.1436/

 

NGK plugs,. 026 to. 028. 1 new coil pack and you should be OK.

 

@Brian R did you get this sorted? Raiders post above this should have done it for you hopefully. also only used OEM coil packs it'll be a bad time if you don't.

 

Sorry for the late updates, I replaced the spark plugs it got a little bit better but the car still feels like it stutters when building boost. Where could I get oem coil packs? Thank you.

 

Dealer is the best option for oem.

 

Might be cheaper than dealership
https://www.tascaparts.com/oem-parts/mazda-ignition-coil-lf2l18100a

 

Thank you for the link I called dealership and they quoted me 105 a piece I’ll order it from that website and keep you guys updated!

Another quick note, when I put the spark plugs in the guy at autozone told me gap was .36 but someone mentioned .28 would this cause the misfire to happen just less severely?

 

Gap size: 0.026" - 0.032"| Preferred gap is between 0.026" - 0.028"

.36 is huge! Shouldn't be more than .032" .036" is probably the OEM spec but through trial and tuner .026"to .028" has become the go to gap for the speeds so definitely gap your plugs in that range.

 

I changed the plugs gapped them to the right gap and switched all 4 coil packs, the problem went away a little bit but there is still hesitation/misfire when accelerating slowly.

I did a compression test all cylinders read between 145-150 .

 

since you replaced the coils and plugs, is it still throwing codes?

 

No more codes but it’s still misfiring I am lost and don’t know where to go from here I will probably end up taking it to a shop this week

 

Maybe it's related to your APP. Might be worth looking into. Do you have anything that could monitor koeo and slowly depress the accelerator pedal to check for inconsistencies?

 

Finally got the mess sorted out, it was a fuel injector that was leaking took it in to the shop and they figured it all out.

 

At least it was something fairly simple and not an internal engine issue causing a miss. Glad you got it worked out.

 

So the first response in the thread by raider that said if after coil packs it continued replace injector seals was spot on

Glad it's fixed