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Discussion Starter · #1 ·
I just picked up my 2012 GT with 100k miles so I'm going through and replacing basic maintenance parts per the discussion I had with my friend who sold me the car. He told me about the misfire and I initially replaced the plugs just for the sake of maintenance and it seemed to do the trick. About 1000miles later, the misfire came back hard! #3 & #4 cylinders so now I have just replaced the coils, all 8, MSD SF coils. On the initial start-up it did throw a "random misfire on start-up" code. I wonder if that's normal following new coils. I drove it around for awhile, did some pulls and held the RPM at 3-4k where it would really misfire before and basically go into limp mode. So far so good. Can't tell if it's actually fixed yet tho.
 

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What are the actual codes?
 

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Through the years I've noticed when there is a drastic weather change my 13 with start with a misfire, and either set a random misfire, or just blink the CEL a bit. This usually evens out within a mile or 2 and then be gone. We have had some big swings here recently but honestly since the Lund tune was installed this has not happened.
I wonder if it is software related.
 

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You guys got me thinking. Though my Mustang has a Kenne Bell Mammouth SC w/Kenne Bell tune, I sometimes get those codes! Happens at first startup of the day. Starts fine then starts stumbling and hunting. Last about 20 seconds. The cooler the ambient temp the worse it gets. Runs fine after that! I only get those codes when it is around freezing. They immediately go away after that 20 seconds. I talked to a KB tech and he said my problem was the amount of alcohol in our gas. It condenses on the wall of the throttle body causing the stumbling. I have an N-Guage BTW, so I can see the codes immediately. I'm unsure if this helps?
 

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Discussion Starter · #6 ·
You guys got me thinking. Though my Mustang has a Kenne Bell Mammouth SC w/Kenne Bell tune, I sometimes get those codes! Happens at first startup of the day. Starts fine then starts stumbling and hunting. Last about 20 seconds. The cooler the ambient temp the worse it gets. Runs fine after that! I only get those codes when it is around freezing. They immediately go away after that 20 seconds. I talked to a KB tech and he said my problem was the amount of alcohol in our gas. It condenses on the wall of the throttle body causing the stumbling. I have an N-Guage BTW, so I can see the codes immediately. I'm unsure if this helps?
The misfire came back today.
I was cruising on the hwy and downshifted to overtake a semi and while coming around it in 4th gear at about 3500rpm it fell flat on its face and the check light flashed for 20 sec before it kicked back to normal.

Since last time, I checked the plugs and replaced the ignition coils with MSD SF coils. Seemed fine until today, even felt like it was pulling stronger.
Now I have no idea what could be doing it.
 

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Discussion Starter · #7 ·
Further update...I had a misfire jump up again. It is really only happening when I'm really pushing the car to accelerate in 4th or 5th gear. I'm wondering if I should be using the next tier spark plugs instead of the OE Motorcraft ones I just replaced a month or so ago. I have a coworker who has the advanced, professional scan tool and he couldn't find anything wrong but that's probably because in normal driving it's actually fine. But I didn't get a 5.0 to drive it like a passenger car. I got it go to the track and from what I've seen since getting it 6 months ago, this car needs some help before I take it to an actual track. I'm at my limit of knowledge for what could be wrong so any advice is appreciated.
 

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I'm at my limit of knowledge for what could be wrong so any advice is appreciated.
With respect! The next thing you should buy is a diagnostic from a professional & competent mechanic. Spend some time and find out who, the go to-guy is, in your area.
 

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Discussion Starter · #9 ·
I was advised to take a swing at seeing if injector cleaner would help and it seemed like it did for a bit but after another fillup it would come back. I went ahead and swapped out the fuel injectors after a few weeks and initially it really seemed to be the fix all solution until this week the misfire returned. I'm getting a compression check done tomorrow and some direction from Fastlane Motorsports nearby in NC.
 

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I'm getting a compression check done tomorrow and some direction from Fastlane Motorsports nearby in NC.
I’ve never been there but they have a great reputation, and I wouldn’t hesitate. I have family in Benson NC, and I’ve been thinking about stopping by there just to check it out.
 

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Wrong post

I just got the car back from Tricky Performance and they checked the car out did a crank re-learn and said that the car is running a little rich which could be effecting the way it runs right now. The engine seems to be a lot more powerful and more smooth, but it still has a little vibration and at idle I can definitely tell there is something not firing right. It could have something to do with the car running a little rich but I feel like it could be a little more than that. Tricky Performance recommended that I get their tune to help with the rich condition, which is what I plan on doing in the next week. Hopefully this solves the issue!

I've always leaned towards no aftermarket coils. When you rechecked the plugs, the gaps were ok?
I did check the gap on the plugs, they are Motorcraft SP-548, CYFS-12-F1 Platinum spark plugs, pre gapped to I believe .053 and they all were in the same range.
 
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