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Discussion Starter #1
I've got a 2006 Mustang GT With 150,000 miles on it. It runs amazing 99% of the time. Every now and then, I get a misfire that sounds horrible. It throws a P304 code, causes the check engine light to flash, and makes a horrible knocking noise with the misfire. It occurs at any RPM, and usually acts up once every 3-4 weeks. I've changed the spark plugs, and have changed all of the fuel injectors. I thought I had it fixed, but I got a nasty misfire once again that only made the check engine flash, and immediately corrected it's self after about 2 minutes. I'd like to nail down what it might be somehow. But it's difficult with it being so intermittent. Any ideas?
 

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That's a misfire code for cylinder 4. Try swapping the spark plug with cylinder 3, disconnect the negative battery cable for a few minutes to remove the ECU fault code, and after you restart the engine see if code P0303 pops up instead. If the code doesn't change, swap the coils and repeat. If it still doesn't change, swap the injectors and repeat again. You'll eventually find the culprit.
 

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Discussion Starter #3
It's got all new plugs, and new injectors. The only things left as far as I know would be a wire harness, and coil packs. It's the knocking that is concerning. I'm not sure if that might be pointing to something more serious.
 

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I agree with bullitt as far as eliminating small, less costly possibilities before diving into internal possibilities.
I would swap coil packs at this point.
 
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Discussion Starter #5
I've swapped the coil packs. Put in the MSD Street fires. I think it's getting better, but I'm not 100% sure. I got on the freeway tonight pushing hard in 3rd, and got the misfire again. Not getting the knocking noise, but the check engine light flashed, and it misfired while accelerating hard. When the vehicle is at idle, I can hear a tick in the engine. It goes in, and out in volume. I'm sure with 150k miles on it, all this needed to be done, but I'm wondering what is next. It runs absolutely fantastic when it's not misfiring. And it doesn't do it very often. But the tick is always there. I'm wondering if the two are related.
 

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Wonder if this could be your issue. With 150k miles you're due for new lash adjusters and rocker/followers as well as full timing gear replacement.
 
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I suggest you use a mechanic's stethoscope or a long piece of rubber hose to localize the ticking sound. This will help us advise on which parts you should replace without you spending extra money on parts that don't need replacing.

You might want to do a compression test on all cylinders to rule out the possibility of a valve problem.
 
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