Hi all, I have a 08 g35 and I'm getting a slight misfire when the car is cold. After the car fully warms up the misfire disappears.

When cold, the car starts fine, idles fine, no misfire (from what I can tell) at idle. But as soon as I start driving it, with throttle at about 10% or more I will hear a misfire. I have changed spark plugs (old plugs looked normal) and checked the coils but misfire is still there.

There are no codes when I scan for them so I'm not sure where to go from here. Maybe injectors?

I looked around and found this video:
My car is basically doing the same thing.

Thanks

 

Are you SURE it's a misfire? You feel a sudden loss of about 20% power? I've seen MANY "cold engine misfires" that were actually very small exhaust leaks that would be more prevalent when cold and under moderate throttle before the pipes have expanded due to heat.

Did you use Denso FXE24HR11 spark plugs?

I would start by following the steps in the FSM which usually go something like.

-Remove fuel pump fuse
-Crank/run motor and run until it stalls
-Crank again 2-3 seconds to remove all fuel pressure from the line.
-Remove coils and all spark plugs
-Check resistance with a digital multimeter between the 3 pins of the coil (pin1-pin2, pin1-pin3, pin2-pin3) verify you don't have one coil pack with an odd reading.
-Physically inspect each coil pack for blistering of the resin encapsulation (shiny black) part on top or burning/scorching/discoloration/tears of the spark plug well boot, or corrosion on the harness pins / spark plug contact spring
-Attach 1 coil pack at a time with a spark plug installed, hold WITH A LEATHER GLOVED HAND the spark plug ground strap (hook part at the end) 1/2" from grounded engine metal or chassis metal (intake manifold works perfect) while a second person cranks the motor and you visually watch spark.
-Rinse/repeat for each coil pack

If you hold the spark plug with the ground strap directly touching the intake manifold it will almost always show spark so you need that 1/2" gap, the system operates at something around 15-20k vdc so it will bridge the gap if everything is working properly. Try to be accurate with that distance, too great a distance causes amp spiking which can damage the coil over time.

 

That having said, I haven't thought about it being an exhaust leak. I never really took notice of power loss since I wasn't accelerating hard enough to notice it, but I'll try that soon.

I replaced with the factory plugs, which were the densos that you mentioned.
I've already checked resistance of the coil packs and all of them were very close to each other.

 

Try resetting the ECU, might be worth a shot, costs nothing and only take a few mins.

 

I had this exact same issue. I believe there is a TSB out for it. Essentially, I just had my local Nissan dealer update my ECU to the latest version and perform an idle air relearn. I haven't had that misfire issue since.

 

update: this morning I gave it a bit more gas when I heard the "misfire" and it accelerated pretty linearly. I didn't notice any loss of power (or vibrations) so to speak. I'll try to test for exhaust leaks sometime soon.

 

Next time it does it go WOT for a second or so and see what it does.

 

Thanks, I will look into that if I find out it really is a misfire.

Just tried that. Had it in manual mode in 2nd so rpms wouldn't go crazy high and had it WOT from 2k to 3kish rpms. The "misfire" got louder when I went WOT, but I didn't really notice any loss of power or inconsistency with power delivery.