I need help I replaced the valve covers on my 03 g35 cause they were leaking. I also put new ngk plugs new coils. I still have a misfire so I changed the connector and nothing has changed. All the others are fine. I don't know what to check now can anyone help me. Thanks

 

You should do a compression test of each cylinder to verify you don't have one that's very low, is it a 100% fail to fire or does the misfire only manifest at a certain rpm or under a specific load? How did the old spark plug look on that cylinder? You can verify spark by removing the spark plug, plug it back into the coil, with a gloved hand hold the ground strap (little hook part at the end of the spark plug) against the intake manifold while someone else cranks the motor and visually check for spark. Also try swapping coils with a different cylinder but that's probably not the problem since the issue existed before and after 6 new coils.

 

I didn't have a misfire before I changed the valve covers. I swapped out the spark plug and coil to number 1 and still have the misfire on 3 the plug if I take it out smells like fuel. I will check if the plug sparks tomorrow that you for that tip.

 

Are you 100% sure you have the coils plugged in with the correct order? Two of the harnesses are very close to one another and can get crossed up. Something else that can cause the issue is a sticking fuel injector but since the issue only happened right after swapping the valve cover I'm more inclined to think something is plugged in wrong.

 

Are you using anti-seize? If not, do so. Sometimes plugs don't seat all the way if the threads are even slightly tarnished. I've had misfires when it was as little as 1-2 threads away from being completely seated.

 

Don't discount the possibility that it could be a screwed up injector. I had this happen to me after servicing the starter on my BMW. After getting everything back together (had to disconnect the fuel line from the fuel rail) I had a consistent misfire in one cylinder. Drove me crazy considering it had nothing to do with the work I had done. You can use a mechanic's stethoscope or even just hold the tip of a screwdriver against the injector body and stick your ear on the screwdriver handle to listen and make sure all the injectors are making the same clicking noises. In my case the injector in the hole with the misfire wasn't clicking. A solid rap on the injector got it going again instantly. It may be low on the likely list of suspects but it's so easy and quick to do..... I went nuts with compression tests and coil/plug swaps etc.

 

@sarah Did you ever find out a fix for this or what was causing it? I'm having the same issue, changed out the plugs and coilpacks and I'm still getting a misfire on cylinder #3 code thrown at me. I was going to clean off my MAF and filter just to see if those play a part, but right now I'm just guestimating. Any info or assistance would be greatly appreciated.