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Discussion Starter #1
My wife recently came back from a drive and told me she was getting a misfire code on the ultra gauge. I checked the codes and saw P0301 P0305 P0300 (and P1300 if I remember correctly). I checked that all the plugs were connected and checked the plugs in cylinder 1 & 5 (cyl 1 looked a little darker than the rest, but nothing too crazy, no wetness, oil, etc). I cleared the codes and am getting P0301 returning. I swapped the plug in cylinder 1 to cylinder 3 and am still getting P0301, so I'm confident the plug is ok. The misfire seems to happen when shifting from 2 to 3 under load on the highway. It idles fine.

Upstream O2 sensors (Denso) are 2k miles old (got a misfire & o2 sensor code soon after I bought it), plugs (NGK BKR6EIX-11) and wires (STI) are a few hundred miles newer than that.

What should I look at next?
 

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You should swap the injectors too
 
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Discussion Starter #3
That was going to be my next guess. I'll order some and see how it turns out. Thanks.
 

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Make sure that wire isn't bad. Damp and dark..... look for arching. Easy to check to make sure before you start buying parts. Also do a compression check just to be sure.

There's so many things that can cause multiple misfire codes. Mine started getting worse and worse and then led to random no starts, but usually ran fine. Stumped 2 shops even who were looking a live data for the cause. It ended up being a crank pos. sensor.
 

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Just went through something similar to this. Change the plugs and wires and it should solve the issue. Start with just doing all the plugs and see what you get. Then do the wires. If I had to do it again, I would change the wires and do the coils as well since everything will be a part anyway. And if was me I would also do the coil relocation kit so I never had to take anything apart again haha.

But wires should fix the problem. If it doesn’t then the coils may be bad.
 

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I did spray down the wires last night and got some arcing where i soaked it enough that there was a little arcing where the water bridged the gap between the valve cover and wires, but nothing jumping through the air. The wires have about 300 miles on them, so I doubt they're bad, but it's possible. I'm going to check my routing and make sure they're not touching anywhere. I do have my old plugs too, so I can swap one back if that doesn't work.

Since the initial codes I've only got the P0301 to come back, so I wouldn't think it would be the coil or crank position sensor, but nothing would surprise me on this thing and maybe I just wasn't driving long enough to get another misfire.

I did hold off on the injectors for now. All of the misfiring was happening on a single tank of gas, so I think I'll try to make sure it wasn't just a bad tank as well. Does bad gas even happen anymore?
 

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My first reply was to swap two existing injectors (let's say 1 with 3) to see if the code goes to 3 or not cos if it does you know that the injector is fubar
 

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There should be no arcing at all. The "spark" should be contained from the coil to the plug only ever say hello inside the combustion chamber. Sounds like it needs wires. If they're that new, you could probably get them warrantied or upgrade like most suggest here.
 

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Discussion Starter #9
I agree that there should be no arcing. The only scenario that I saw it was when the water bridged between the wire and the valve cover. I wouldn't consider that normal operating conditions. I did check the routing (looked good) and re-dielectric grease the boots as well as fill up at a different gas station. I haven't had the misfire return in 6 trips totaling ~50 miles. I'm not convinced it won't come back, but given that it was happening on every trip, one of those things definitely helped somewhere.

The wires have a lifetime warranty, so I can always swap those out if/when it returns.
 
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