I have a 2004 G35 sedan 6mt. I just put a new engine in it along with a Z1 motorsports lightweight flywheel and clutch and AMS pulleys. Before install of the new engine I put new plugs in. After 200 miles of driving I dumped in some STP fuel injector cleaner and literally 2-5 miles down the road I got a P0301 # cyl misfire code. After reading the code I swapped plug and coil with spare parts I had. Still had the misfire so I changed fuel injectors and intake gaskets. Still had a misfire. Next, I checked the compression 150psi in every cylinder on that head. So after changing the plug, coil, injectors, intake gaskets, and doing a compression check I STILL HAVE P0301 misifre code.

ANY IDEAS WOULD BE GREAT.....thanks again guys!!

 

Did you try and move the coil from cylinder 1 to a different cylinder to see if the misfire follows?

Why did you run the fuel injector cleaner so early on a new motor?

 

Yes I swapped the coils...P0301 still....I'm going to try this again. And let me rephraise that..new to me 70k on the engine that was just put in.

 

Have you gone through the full tank of gas yet?

 

Ive gone through a quarter tank,...why do you ask?

 

Did you reset the ECU? Also do you feel the misfire or does the car run normally?

 

Yes, I have reset the ECU. The miss is definitely noticeable....along with unburnt fuel smoke coming out of the exhaust and in the engine bay. After checking injector, plug, coil, intake gaskets and compression I am clueless.

 

One thing I haven't checked is spark plug gap. It honestly did not cross my mind so that will be my next step. Check gap and use three of the coils I have that I know are good 100%

 

May be its the connector for the COP. If that is fried then your COP might be functional but isn't getting any current. I have no idea how one would test that though.

However, since the problem started after the injector cleaner, I am not sure if a fried connector would be the issue but it doesn't hurt to check it.

 

I've thought about this. But the number one cylinder still fires fine.....I have a spair wiring harness so I have a spare pigtail for the coils. I honestly don't think this is it but am going to try.....I think my next move is going to be check plug gaps...swap the coils on that head with other coils I have that are good top off the fuel tank and see what happens

 

My biggest advantage right now is that I have spare parts including an engine harness 13 good coils 12 good injectors 12 good plugs and doubles of every sensor on the engine

 

Lol the advantages of swapping engines haha.

Btw would you mind telling me how much you paid for the used engine and how much it cost you to get it swapped?

Also since you already swapped the plugs, not sure why the gap would be a problem...

 

The engine was 850 included everything from pan to plenum and exhaust manifolds. I swapped it myself and at the time of the swap I grabbed AMSpulleys Z1 motorsports silicone hoses and a z0Z1 motorsports ligtweight flywheel and street clutch.

 

Dude any luck?

 

Did new plugs swapped all three coils still missed...but at this point the miss cleared ou above 3k rpm...disconnected the evap return line off of the fpr and the miss went away drove it for a few miles like this put it back on and has been running fine since.....maybe blockage in the evap causing pressure instead of vaccuum created a miss idk...but in short yes I had luck...hope this helps somebody else someday thanks guys!........btw the car will be for sale in the next couple days after I tie up a few loose ends and put a couple miles on to ensure everything is operating properly