I have a g35 and i have got code P0304 from the ECU at autozone, The problem first occured after i filled up my car with premium gasoline, the car wouldnt turn over and the vdc and CEL came on along with power steering went out, I let the car sit for 10 min and the car was fine and i made it home and it started the next morning the next day the car started fine and ran well for my 15 minute commute to and from work, it was fine for 5 days until i filled up at chevron the other day and right when i got home 1 mile later the engine shut off and the same lights came back on but it started up again but not at first after 10 min what is the cause of this

 

Have you been putting premium gas in all the time? You said premium like you haven't been doing that since you had the car.

 

What grade fuel shouldn't matter. The sedan CAN run on 87 octane without issue. It will just sacrifice a little power/economy when you run 87.

Anyway, the OP's comment confused me

Car not turning over implies the starter did not engage and physically spin the engine. The power steering doesn't function without a running engine. So i'm confused as if you meant the engine cranked but didn't start, or nothing happened when you turned the key.

In terms of your CEL code.

P0304 is a cylinder #4 misfire. Cylinder #4 is the driver's side MIDDLE cylinder.

I'd check the coil and plug on this cylinder and inspect to see if oil from the valve cover is leaking inside. If the plug hole looks dry. Swap the coil to a cylinder next to it, erase the code and go for a drive. If the coil is bad, you should get another CEL with a new code pointing to the cylinder you moved the coil to. If that's the case, replace it.

How old are your plugs?

This could also be a failing fuel injector as well, or low compression in the cylinder, but the plug and coil are easiest to start with.

 

I too chased the common p0304 code a little while back and ended up changing all plugs (NGK iridiums), #4's fuel injector(found a clean used set for dirt cheap); and even after that p0304 still showed up- car was still misfiring. It was after I rewired the knock sensor harness and re-heatshield'd it the car finally went back to normal. EDIT- the knock sensor harness is also a known issue on these cars. I'm assuming your motor is a pre-HR VQ.
Although I did not have any turning over issues. In any case I truly believe there's something voodoo about cylinder 4 as it seems to be a common topic issue via search.

 

This voodoo of cylinder 4 popping up in OBD scans is true. Happened to me a few weeks ago on my stock block. A similar post recently: https://g35driver.com/forums/engine-...300-p0304.html

After testing coil packs, and replacing plugs with new NGK Platinums...I've come to testing injectors and replacing all sensors (since my block has over 100k).
Lastly..everyone seems to refer to the FSM (factory service manual) which says to perform the: “Idle Air Volume Learning” and “Throttle Valve
Closed Position Learning” ...pretty easy to do with practice. I haven't been driving the G since I'm getting a new motor installed, but if I buy a used injector for cheap, I'll do the rest to identify the problem.

 

Update...actually..I think my valves on cyl.#4 are done. It makes more sense because I get valve chatter at high rpm, white smoke (w/normal oil temp), and misfire. I'll do a compression test for the hell of it, but new motor is dropping in soon anyways.

 

Here is some more information that I have to date:

1. Car runs fine on short trips or any cold start for at least 15 min or 10 miles

2. Replaced Crankshaft sensor (Not camshaft sensor yet)

3. Car will only die when i am slowing down, at a stop, or when accelerating from a stop (car is fine when i am on interstate or cruising at steady pace on road)

4. Car runs smoothly at first on cold start but, then once car is warmed up you can feel car running hard and lurching

5. If car does stall it will turn back on but it takes much longer cranking and does not sound very clean (It also does this if the engine is heated up)

 

Should my next step be replacing Camshaft Position Sensor(s)??? If so which one? or both? If not what other next action should i take for troubleshooting this problem???

Also i live in Phoenix, Arizona so if any good G35 mechanic is in the area and works for cash send me a DM......

Thx for any feedback always very much appreciated

 

how did you fix this issue?

 

P0304 is usually either the spark plug or the coil pack. It's a specific error code for cylinder 4 misfiring.