P0301 Misfire Code that won't go away.

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2007 Mazdaspeed 3
Well, here's my problem. After reading and searching, combined with multiple attempts at repair, I have a misfire code for cylinder #1 that won't go away. I've replaced coils, plugs, switched plug manufacturers twice, checked the common things ( leaks, tears, loose clamps ) and changed gas stations. My car has a Cobb SRI, Forge BPV and exhaust (cat-back only). I intend on re-setting the ECU after putting the stock parts back on, but before I do that I don't want to waste time and possibly have the same problem, and I can't justify swapping plugs and coils time after time. The car averages around 25 MPG, runs and drives fine until WOT higher boost situations, then it begins to sputter and pop through the tailpipe combined with the overall loss of power... driveability shows no other issues. I don't have a tune, no Dashhawk, but I have a scan tool that lets me see certain parameters in real time. Any suggestions as to where I should go next?? Thanks in advance!
 
When you say it "won't go away" have you used your scan tool to clear the code to see if it comes back?

If you tried that and it came back, then, by all means just reset the ECU (disconnect battery negative terminal, stand on brake pedal to bleed out any residual current, let sit a little bit, and then reconnect battery and try.

My guess, however, is that if you are having the WOT drivability issues, then something is amiss.

A simple thing to do is to check plug gap. Many brands of aftermarket plugs for our cars come with a very wide gap. Make sure that they are gapped down to .032" or even a bit tighter. You'd be surprised how a wide gap adversely affects WOT performance.

Next up thought in my mind would be a bad DISI fuel injector on that cylinder. Swapping injectors to test that theory is not so easy on our cars. Might at least try to run some fuel injector cleaner through your tank first.
 
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I've cleared it with a scanner and it's come back within minutes, but after work today when I check things out will be when I reset the ECU. I have the plugs gapped at .030" currently. I use injector cleaner once a month or on the fifth fill up, whichever comes first. Perhaps I'll try some fancy Techron or Lucas along with this next tank of gas. I hope it's not an injector...
 
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Well after returning the car to stock, re-setting the ECU, 4 new plugs, moving the coils around to different cylinders and a brief drive around the block, I still have a misfire and I now have the distinct sulfur or "rotten egg" smell coming from the tailpipe. I'm assuming one or both of the factory converters has gone bad, which should explain my driveability issue?
 
I had the same problem on my 2007 Mazdaspeed 3 come to find out the it was just the a bad spark plug
 
Plugs are new, gap set at .030". I moved the cylinder #1 coil to cylinder #3 and the misfire code followed it. Swapped another new coil into that cylinder and still showed cylinder #3 misfire. I'm convinced it's a bad batch of coils from our supplier at work, going to try using the 4 stock coils again before I get them new from the dealer. The smell from the exhaust concerns me too, not sure if it's because of the misfire issues I'm having, or if it's the cause of all the problems.
 
Engine misfires can CAUSE damage to the catalytic converters. Not saying that is what is going on. The unburned fuel goes out the exhaust valve and manifold through the downpipe and gets re-ignited in the catalytic converter. Not good for the life of the cat.
 
Misfire has gone away now for two complete 70+ mile drive cycles. I put the original coil packs back on the car and haven't had an issue since.
 
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