Hey everyone I got a 2004 infiniti g35 coupe. I was having a valvue cover issue prior to this problem so I had it replaced and when I got it back the p0300 code appeared and the note of the exhoust is completely different i changed the sparks and changed the coil packs and i still had the same issue. I had a couple of my personal machines check it out and he checked and gapped the sparks and checked the coils as well and said everything looked fine but my cat was getting red hot on one side. Most likely due to the misfires. I finally took my car to a reliable shop and got a diagnosis the shop said they found the missfire on cylinders 2 and 4. The shop also said that the coil packs and sparks are good. They did a compression test and the vehicle has good compression. He noticed that the top of the pistons on 2 and 4 looked clean so he suggested I changed the fuel injectors. I changed all 6 of my fuel injectors and still no go but the car note is improving but at this point I'm stumped any suggestions. She's pretty rough right now

 

Sounds like the coil pack harnesses got mixed up. Check the wire harness COLORS on the coil packs.

 

I had the shop diagnosis and they said the coil packs and spark are fine does that mean they should plugged in correctly or what do u think do u recommend I double check them

 

Cylinder #2 & #4 are right next to each other, located on the drivers side and the forward most cylinders on that bank of the engine. Its much easier (and common) to cross #4 and #6, but I could see #2 & #4 getting mixed.
It could also be that the cat on that bank is clogged or clogging up.

 

I am having the same issue with the same year car. I had a mechanic change out my valve covers and now i have a misfire. He pointed out that my Cat was turning cherry red and that it was probably clogged and causing the misfire. I removed the CAT and sure enough the driver side honey comb was completely loose and at the back of the pipe. I replaced the CAT with test pipes, new spark plugs and all new coil packs, replaced all the gaskets and visually checked all the connections and still having a misfire. Codes i get are P0300 Random/multiple cylinder misfire and P0327 knock sensor 1 circuit low bank 1 or single sensor. I have knock sensor ordered along with new harness. At this point I really don't know what to do either. I hate just going through and replacing parts.
I might replace the fuel injectors but would like to know what success others have had with this issue

 

As Cleric mentioned earlier, check/verify the harness connections to coil packs. It's very easy to swap the #4 and #6 harness connectors, as well as others. I used paint pens of different colors to help remember what was plugged in where.

P0327 I had a few months ago, and was solved by replacing the knock sensor and sub-harness, which you ordered. A rat chewed through mine lol.
Note that it is challenging to remove some of the fasteners towards the rear of the engine, particularly the ones that secure the knock sensor harness, I used zip ties in their place.

 

I have printed off the color code for the harness and will check it out when i get home. I hope that it is something that simple and not a blown piston ring as i have read in other posts.
Thank you for your reply

 

yea im still having the same problem im completely stumped the sparks and the fuel injectors i replaced are oem and the harness seemed to be plugged in correctly i dont know were to go from here

 

I needed to update my issue and maybe it will help you. I have fixed my misfire, my coil wires were crossed. It is easy to do because the wires that go to cylinder 4 & 6 can get switched because the 2nd wire coming out of the harness actually goes to cylinder 6 and the 3rd wire goes to cylinder 4. I did have to replace my CATS because the driver side was clogged and the honeycomb was completely detached and at the back of the CAT. I believe that because of the misfire all the fuel that passed through to the CAT clogged it.
check out the link below and go to 4:30 in the video.

 

For anyone having a misfire after messing with your valve covers or spark plugs, like Cleric said, u probably have your coil wires mixed up. It is very easy to mix them up due to their location on the harness.


Swap the plugs going to coils #4 and #6. They are on the (left) driver’s side. Middle and aft coil wires.

Do this first before u try anything else. Do not drive around or let the engine run for a long time if its misfiring. You will damage your cats or O2 sensors...like I did

 

Literally the same exact problem, the connectors for cylinder 4 and 6 were swapped you saved me such a headache lol. Unfortunately my cat is clogged and still needs to be replaced

 

this tread fix my miss fire I definitely mixed up #3 & #5 mixed up thank y’all

 

Could you share a picture of the plug order of the coils and is this also possible on a 2007 Infiniti g35?

 

I can show you how I had got mine switched up. It’s very easy because you would think 3 goes to 5 because of the length and position. But I will post pictures later for you

 

Just check the wire color on the harness, each harness has three wires. White/blue stripe is 12v power, black is ground, and a third wire that goes to the ECM

The third wire will be a different color on each coil.

Cyl1 - yellow/red stripe
Cyl3 - blue/red stripe
Cyl5 - purple/white stripe

Cyl2 - green/red stripe
Cyl4 - grey
Cyl6 - grey/red stripe