Ok, so this code is driving me crazy. About 3 weeks ago my car CEL turned on. I thought no biggie its probably my 02 censor so i didn't worry about it. Kept driving CEL went away. Two weeks later boom its back in worst this time. Cars CEL starts flashing like crazy i was like WDF. It stuttering and having a very bad acceleration issue. It also has a gas smell.

It idles fine when its just sitting there. Its only when u get on the throttle that it doesn't respond good. It's like it hesitates and when your WOT it feels like there is something preventing it from functioning right.

So i checked the code an it a P0300.

Things I've changed
Spark Plugs = NGK Iridium with correct gap
Brand new Coil Packs =BECK/ARNLEY Part # 1788317
New O-rings for injectors
A couple of vacum lines
Oil Change
Negative Ground Cable ( car used to randomly turn off different issue)
ECU reflash by Nissan
MAF
02 censors/ Megan racing HFC
New Y-pipe ( old y pipe had 2 holes in the elbows)

Things i think it might be
1.Bad Injector ( i have 6 new injectors in my garage just haven't installed yet)
2.Bad Fuel Pump
3.Clogged fuel Line
4.ECU
5. Bad Compression on one of the cylinders or more

Ive already spent to much money on this car but i don't want to sale it or get rid of it since im so close to paying it off about 700 bucks before its paid off

So do you guys have any suggestions? Or should i just take it to the dealership for a diagnostics ??

Or should i say F*** IT and get me a different car.

BY the wayt its an 03' g35 coupe with 114k on it

 

So it turns out it was either bad gas or the stock Y-pipe that had two giant *** holes in the flex pipes.


Put the new Y-pipe in but car was still driving like ****. About 3 days later SES code when away car ran like a champ. Guess it just took a couple of days before the ecu recognized the new Y-pipe.

 

How would the Y-pipe cause misfiring?

 

To be honest i have no idea maybe No back pressure. 02 censors weren't reading at all.

All I know is that after I put that Y-pipe i was more quite but still running bad. And after about 3 days no more random misfire. I didn't change anything else besides that y-pipe at that point.

 

it might come back, do a compression test ,could be your rings, does it smoke?

 

I will do a compression test if it comes back . No at the moment it doesn't smoke at all. Still running good at this time.

 

I had the same issue with mine, set in the garage for 8 months no money thinking i was going to spend alot of money after taking it to the Dealer they said had to change Rings and injectors. that wasnt the case i finally decided to work on it and changed all spark plugs and Coil packs that fixed a little but still would do the same ended up checking the cats and they clogged up guess with all the miss. that it was doing ended up messing up the cats if u havent already check the Cats might be a possibility for you too. since cats are tooo expensive factory put Megan racing test pipes and that did the Fix man try it before spending money on more diag.

hope it helps

 

I just had the same problem. I found the coil that was the problem and replaced it. It ran fine for about an hour then it started misfiring again. I pulled the coil again and found a pinhole in the stem that goes to the spark plug with evidence of arcing. I sprayed a coat of plastidip to fill the hole and then wrapped it generously with electric tape as a temporary fix/trouble shooting patch to see if it behaves now.

One thing to note is that with the random misfire code I couldnt tell what cylinder was acting up. So I went out back and noticed that exhaust on the passenger side was coming out rough and that narrowed it down to the coils on that side of the car when i first was trying to figure out which coil was bad.

 

Your ypipe wouldnt cause that. Your o2s dont read back psi. And im pretty sure our Gs dont have EBP sensors. Youre looking at an electrical issue. Especially that the cel came on. With the cel flashing/blinking mainly means a catalytic failure which is why your car went into limpmode. I would watch for the problem to come back.

 

I just test ran the car for about 30 mins. It ran smooth and had a hiccup or two which tells me the repair worked. Im gona order a new coil stem thingy and call it a day. However I bet i can fab a permanent fix on the stem pretty easily. I pulled it apart and the only working internals is the spring mechanism that transfers energy from the coil pack to the spark plug. The plastic part of the stem in just an insulating sleeve.

 

I had already spent an arm and a leg on this car so my last resort was the Dealership. The weekend I was thinking about taking it started acting fine so that saved me a **** load of $$$$.

I already have Megan High Flow cats so I know that wasn't the issue. The o2 censors were all brand new as well so eliminated those as well.

Yeah that Random Misfire Code is a Pain in the a$$ . Its not that bad if its just 1 coil or spark plugs but if you change both and you still have a misfire then its when its get expensive $$$$

 

Im dealing with this as well. I need to see about coilpacks but my cel went away not sure. P0300 is a tricky code.

 

Yeah the code will go away and then came back this is my 2nd time dealing with this issue. But thank GOD I think this time it will NOT come back if it does I'm getting an ls1

On the plus side i got to spend a lot of time with my G lol

 

I found yesterday that my stems had tiny cracks in the and were arcing. So I painted them with liquid electric tape all the way up to the boot. My mechanic also showed me how to find out which coil was bad. Its easy on the passenger side. But on the drivers side remove the air tube and unplug the MAF so the car can run. Start the car and unlpug the oils one at a time. If the idle drops then the pack is still good. If not then thats ur bad coil or stem. Yes cracked stems can be fixed.

 

^^Great tip for anyone having the same misfiring issue !! ^^^^