So I’ve seen this thread posted a million times on g37 and 370z forums but none of the threads had any solid answers or really any answers at all.

I've got a 2009 G37S 6MT Sedan with 110k miles. I put a 2016 Q70 3.7 engine in it about 7 months ago. Only mods done are ISR Test Pipes, HBP Single exit catback, Z1 lightweight flywheel, and CMAK Slave Delete.

90% of the time the car starts right up like normal and drives off, but every now and then especially after I turn off the car and come back after like 20 minutes, the car will start right up and just stall. Transmission is in neutral everything is normal but the car just starts and dies right after.

This will happen about 2-5 times in a row and then it will start and ALMOST stall then kind of fix itself up and idle. Only way I’ve found to get it to start without dying is to gas it as soon as it starts.

Now I’ve been having issues since the engine swap with the car running rich. I’ve tried everything from new intake filters, new and clean injectors, new fuel pressure regulator, cleaned MAFs, swapped them out with new ones and reset the ECU, fixed my exhaust leaks, pretty much everything I can find that would affect my AFR.

The car still has very loud and very noticeable pops whenever I shift or let off the gas anywhere higher than 3k rpm. The car is also much slower than it used to be with no difference whatsoever to any mods.

The stalling problem started about 2 months ago but the popping has been going on since the engine swap. I also put on new spark plugs after the swap just to be safe.

I have no CELs and no idea wtf is going on. I’ve already reset the ECU countless times and relearned the idle with an ECUTEK plug in. I’m stock tune and on the same ECU that came with the car stock.

Also posted pictures of my spark plugs to see if that helps with anything.

 

Also spark plugs have about 6k miles on them at this point

 

Are you still running the oem fuel pump?

 

Yes everything that wasn’t mentioned is oem

 

To my eye, those plugs are not showing signs of a rich condition. If they were rich, there were be a little black soot on the threaded ring (where the ground electrode connects to)

What are your short & long term fuel trims for each bank?
Have you checked fuel pressure?

 

You mentioned MAFs but have you cleaned out the throttle bodies?

I've had 4 different VQ37 cars now that have all had this same exact problem over the years, and cleaning throttle bodies fixed it every time.

 

I haven’t checked the fuel pressure since these cars don’t have a port to check it with. I bought the cjm kit to tap the fuel line and measure it but it’s hasn’t gotten here. I did replace the regulator/dampener though as well as the line that came with it. I’ve checked fuel trims but I’ve checked it on ECUTEK and it’s shows percentage. Usually hovers around 88-97% both banks with the occasional drop but don’t take my word for the fuel trim because I don’t remember much.

 

I haven’t cleaned them recently but I cleaned them out about 7k miles ago