So I have an 03 350z with an fx35 VQ35DE and a 04 G35 trans 6sp. I have replaced all the sensors. All the plugs. The coil pack. Dropped the trans to check the flywheel. New wore harness (compared grounds from another z) had the ECU check and cane back good. No CEL lights. fuel is getting to the engine fine. Did a spark test and couldn' get anything. ECU is stock came with the shell.. engine does have compression. Everything seems fine. Just won't spark. My thoughts are; bad ecu or wire harness. I have also replaced the fuse boxes and battery if that makes a difference. I'm getting grey hair from this thing lol.

 

I would see if you can borrow or use another ECU, wire harness, well you're just going to have to buy and use a new one to find that out. I'm sure there are ways to test but I would just start fresh. But if that's not your problem it's a waste.

Have you taken the coils or plugs out to see if it's actually giving power to the plugs while you crank?

If not follow the trail back until you find spark and find out where it stops.

 

I say just go through and re-check everything. You could've simply overlooked something with all that replacing. Double check your grounds, and make sure that your fuses/relays are in the correct spot.