P0301 cannot find the cause
 

09 370Z 69K miles

About 10 days ago on my way home I pulled off interstate and got $15 worth of gas at a gas station i dont usually attend. Right after I left and was on the on ramp to interstate it started to miss, on the rest of the way home, anytime I was driving up an incline it would also miss. I figured bad gas right away. The next morning I drove into town and put in a bottle of Iso-Heet and topped the car off with 93 octane from a reputable gas station. Problem persisted. It threw a code and I got it read and it was a P0301 (cyl 1 misfire), I changed all the plugs, all looked ok except cylinder 1 was caked with carbon, was not oily or anything. The problem got a better by a small margin but persisted. I added a bottle of seafoam to the tank to try to clean the injectors with no luck. So I pulled the fuel injectors and cleaned them. While doing this I also swapped the #1 injector out with the #2 cylinder in case I had not cleaned it properly the misfire should switch cylinders and I could identify the bad injector. I reset the code and after a little driving the CEL came back on and was still reading P0301. I then replaced the #1 ignition coil, no difference. Yesterday I pulled the ignition coil and plug so I could make sure it was getting spark. The plug I had replaced just a few days earlier was already caked with carbon. I replaced the plug and verified it is sparking correctly. The problem still persists. Im kinda lost at this point and could use any advice or direction as to where to look next. Thanks.

TLDR: Cyl 1 misfire, possible bad gas, replaced plug(heavy carbon deposits), added seafoam, cleaned injector, replaced coil pack, Replaced spark plug again(Heavy carbon deposits), dont know where to look next.

Replace the injector.

Even though I swapped it another cylinder and the misfire didnt change cylinders?

If the injectors weren't swapped for long (ie, not long enough for #2 plug to foul) and the #1 plug had already begun to foul when you swapped, you might get your symptoms.

If they are the original injectors, I'd say it's worth a try to put a new one in #1. And put a new plug in #1 - might want to inspect #2.

Looks like your fuel injector/s need to be replaced not a cheap fix. Also I would replace your spark plugs at the same time if you had a misfire and your coils inspected and tested. Nissan highly recommends only using top tier gasoline like Chevron or Texaco gasoline with Techron in all Nissan and Infiniti models and you should be using gasoline with a 91+ octane rating FYI.

I pulled the #1 and #2 plugs today. The #1 plug has fouled again, the #2 plug looked just fine. I think that in this case I can effectively rule out the fuel injector as the potentially bad injector is now in the #2 cylinder.

I've read that low compression could lead to that, so Im gonna do a compression check tomorrow and see how that goes. Anything else you guys can think of that can cause dry carbon fouled plugs?

Definitely get a compression check done on your Z to find out the true over all health of your engine. I am wondering what the compression is on both sides of your engine?? Carbon fouling could mean a lot of different things going on with your engine. For one a overly rich Condition happens more times than not.Carboned up/dirty air filters,intake tubes,upper and lower intake manifold runners,dirty MAF’s,dirty PCV valves,and not changing motor oil on time is for sure. Get a decarb/fuel injection service done as soon as possible. What brand gasoline’s are you using in your Z? I would hope you are only using a top tier gasoline brands like Chevron or Texaco with premium Techron additive. Low quality gasoline’s (generic additive) add a lot to carbon build up in your engine. Nissan recommends only using “top tier” gasoline’s in all Nissan and Infiniti models. Low compression,vacuum leak/s,too low or retarded timing,using the wrong heat range spark plugs could all be possible culprits. Sounds like your Z was not very well taken care of as far as doing all your general maintenance go’s.