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Hi guys!

Decided to take the beast out for a spin a few days ago, and noticed that the engine was running a little rough but no codes came up (Max speed was around 50mph). I took it out again and was driving on the freeway (Max speed was 65-70) and then I received "Service Engine, Reduce Power" Code. I plugged in a scanner and got a P305 Cylinder 5 misfire.

I replaced all 10 plugs about 3k miles ago, plus 2 new coil packs (including #5). I swapped coil packs was still getting a misfire on #5. I swapped the Ionic Modules, still the same misfire. What else is left for me to check? I take the car out every 2 weeks, currently sitting with 95k miles. I'd appreciate any help thank you!:grin
 

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Clean or replace the MAFS. I had same issue after a few runs at HPDE days at Mid Ohio. Hot days and hard driving. I changed plugs, coils and injectors. did it again last week. Always reads misfire in #5. M5 boards suggest looking into your MAFS.
 

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I’m having this same issue as well and can not find any leads on it. Anyone able to fix this issue?
Misfires can be caused by a number of things, there's no one magic bullet for it so you'll need to trouble shoot.

Did you attempt any of the fixes listed here? Is it persistent from start up? Only under acceleration?

Clean out/swap your MAF's, swap ionic modules and the ignition coil to rule them out if misfire doesn't jump around banks/cylinders after each swap. I'd then try a new quality spark plug, then fuel injector.

After that it's bigger money to replace parts namely the idle air actuator and throttle body actuator.
 

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If the easy stuff checks out (spark plugs/coil packs/injectors/seals around the tb), it may be time to check for mechanical issues. Broken spring values aren't that uncommon.

If it's just one cylinder, I wouldn't be throwing incidental parts at (idle actuator, mafs etc).
 

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Do you notice any smoke coming out of the exhaust? The only other thing to check is the injector and compression test.


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Thanks for the insight, the code and limp mode would come on randomly. Usually after driving for a bit. I have swapped the coil packs and hasn’t come back yet. If this doesn’t work I’ll try swapping MAFS with a friends car. Thank guys, I’ll report back with results
 

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Swapped coils packs, plugs and MAFS(my friend had an extra set lying around) and have driven the car about 85miles since the code came back. It only came back for a second and when I restarted the car it was gone. It stayed in my pending codes when I pulled it up. Pretty confused at this point seeing the only thing left could be the fuel injector? Cars has 127k miles and runs well besides this, pulls hard and no other issues(yet) lol
 

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Swapped coils packs, plugs and MAFS(my friend had an extra set lying around) and have driven the car about 85miles since the code came back. It only came back for a second and when I restarted the car it was gone. It stayed in my pending codes when I pulled it up. Pretty confused at this point seeing the only thing left could be the fuel injector? Cars has 127k miles and runs well besides this, pulls hard and no other issues(yet) lol
Keep your eye out for white smoke out of the tailpipe if the missfire starts again, also see how the idle behaves. Most common injector failure happens when the injector gets stuck open. If you are not seeing any of that it might be that the valve spring is starting to fail? Too early to know for sure though


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