I recently picked up a 2006 G35X planning to fix a coolant leak, and lo and behold, it starts misfiring as soon as I fix it and tag it.
Long story short, I found some cheap off brand spark plugs in the car, and a melted coil in cylinder 4. I replaced all 6 with NGK Iridium, replaced the coil, cleaned and checked the grounds and all the usual stuff (ensured power/ground and signal at the coil, everything looked good) and at that point, the misfire moved from #4 to #1.
I scoped the cylinder after pulling the plug, and it was soaked with fuel. You could see fuel dripping from the intake valves when it was primed, so I pulled the plenum to swap the injector and saw that the runner was full of fuel, while the rest were dry… confirmed to be a leaky injector. I swapped the injector, put it all back together… and it’s still misfiring like crazy and pouring smoke (raw fuel smell). I pulled the plug again, and sure enough, it’s still overrun with fuel.

I checked compression to be sure there wasn’t something deeper going on, and it was about 150 PSI (good enough for me on a cold engine that’s being soaked down with fuel).

I swapped out the coil with a spare just to be certain that it was good, and that changed nothing. I hooked up the oscilloscope and ensured I had a good waveform, comparing it to cylinder 5 (most easily accessible) and they look identical… no problems there, so ECU should be okay.

What else could this possibly be? All I can think is that I accidentally put the old injector back, as about 3 people showed up at my shop as I was doing the job and distracted me, but in the case that didn’t happen (I don’t think it did) I wanted to cover all the bases first.

 

Your injector wire could be shorted out somewhere causing it to spray all the time??

 

I suppose it's possible, but listening to the injector it sounds like it's firing when it should.

 

Swap the injector with another one on that bank and see if the problem moves to that cylinder.

Also, verify you can SEE SPARK on the sparkplug, leather glove, hold the ground strap near the intake manifold while someone else cranks the engine to see if you visibly have spark. Might just be something else going on like a factory defective spark plug or other issue.

Also, are you 100% sure you didn't mix up the coil pack harnesses? It's really easy to do

 

Yup, 100% the coil harnesses are correct. Been there, done that lol.

New development though... it turns out the #1 injector is NOT firing. Interesting considering the last one was flooding. Anyway, I unplugged it and checked for pulse with a noid light, and there's nothing. Probed the power side with a test light, and I have a nice bright light, plenty of power. It would appear it's not getting pulse from the ECU.
Next step will be to check for pulse at the ECU connector, if so, there's an open somewhere in the harness. Probably around where it comes into the plenum. If not, maybe a burned out injector driver in the ECU? Is that a thing on these cars?
Oh well, we'll worry about that when the time comes. I'll update this thread once I see that the ECU is providing pulse.

 

So I had checked the wiring between the ECU and injector harness, and it ohms out under 1 ohm, so I don't suspect any issues with that. I ended up melting the coil on cylinder 2 now, at which point I confirmed grounding at each coil, and ensured all of the engine ground are clean. I also checked and cleaned the ECU ground behind the glove box.
I checked for pulse at the ECU and it looked good oddly enough, but there are no wiring faults. Weird.

Anyway, I had the noid light on the #1 injector when the cyl 2 coil burned up, and once that coil melted, the injector pulse came back.

I had grabbed an ECU from the junkyard just because I was there, and it was a 2006 G35X so perfect. After ruling out any other issues, I took a shot in the dark and swapped the ECU and programmed it. Started up, ran great for about 30 seconds... then it melted the #1 coil. Good news is I still have injector pulse, but this coil melting issue is getting annoying.

Anybody know what could be going on here? My mind immediately goes to a grounding issue of some sort, but everything is well grounded. I also checked the harness visually along the valve covers to make sure the coil wiring didn't have any issues, and everything in there looks perfect.

 

Check out these two threads:

https://g35driver.com/forums/engine-...acks-help.html

https://g35driver.com/forums/engine-...agnostics.html

 

I had seen those, I'm thinking that condenser may have something to do with this. I would have assumed a grounding issue based on this being random coils each time, from what I can see based on resistance and voltage drop tests, everything is very well grounded. A test light between the coil ground wires and B+ is nice and bright, so they seem very well grounded. Same for any point on the intake plenum, etc.

 

I pulled apart the harness along bank 1 to check the condenser, and it tests within spec (over 1 mega ohm) so I don't think that's going to be an issue. I replaced the cylinder 1 coil, ran the car for a few seconds, and pop goes cylinder 2 again. This is getting EXTREMELY annoying now.
I went ahead and thoroughly cleaned all of the grounds for the battery and engine, there is under 40 mV of drop between the battery negative and engine, so I really don't think there is any sort of grounding issue. What to do now?

 

U got the correct spark plugs? How do the spark plug wells look? Is it full of oil?
Are u sure you are pressing it down all the way until it clicks onto the spark plug?

 

Yes, they are the correct NGK platinum plugs. Spark plug wells are clean and oil free. The coils are definitely in place correctly.

 

Well damn, I cant think of anything else. 🤔

 

Yeah, that's the predicament I'm in now! This is a weird one.

 

Well after burning through 5 coils, I think I got it sorted out. I cleaned up all the ground points and added two 12 ga ground wires between the intake plenum and chassis, and so far so good. I beat on the car a little yesterday and it's still running great.
This is absolutely wild to me that these cars are this sensitive electrically. They seem to be sufficiently grounded from the factory, but I guess they aren't.

 

Good to hear u figured it out. Update this thread if anything changes.