Hello everyone, i own a 2007 G35x with the HR motor and i've been dealing with some strange issues. Firstly on cold start (& letting the car sit for a few hours also) it struggles so bad to start like it's either out of fuel or is looking for its idle then when i give it gas it's goes normal. and if i shut it off and start it right after quickly it starts normally. i've already tested my fuel pump and it's delivering enough fuel, ive checked my plugs which were changed in december 2023 (NGK Laser Iridium) and i've tested all 6 ignition coils and are working in good order.
Secondly under light acceleration at around
1K-1.2K rpm it would dip then continue normally & in 4th and 5th gear trying to accelerate past 2k rpm it would bog and i'd have to firmly press the gas for it to start accelerating. all suggestions are appreciated. as for mods, I have Berk test pipes & custom 2.5 long tube intakes, car is not yet tuned

 

How many miles? Sounds like a fuel issue - potentially a weak fuel pump. Grab the torque app or any other one that can map AFR and see what you get under heavy acceleration/WOT. It should dip into 11-12s. If it's running in 13-14s - too lean and fuel pump is probably on its way out. You can also cycle the ignition before starting cold to see if that helps. If it does, it would further confirm fueling issue.

See if any of these threads are useful. Mine is the second one that I chased down to a bad fuel pump (posted pics). First thread, the OP narrowed his issue down to cam sensors.

https://g35driver.com/forums/v36-eng...-restarts.html

https://g35driver.com/forums/g35-sed...er-5-5-5k.html

 

Yeah it definitely turned out to be my pump that was failing. I got desperate & replaced the battery yesterday let the car sit for a bit and it still was starting weird. So i finally decided let me get a brand new donor pump from a 2008 and installed it earlier this morning primed it about 6 times before initial cold start, & boom car started right up strongly!!! been chasing this issue for literally 3 months lol, took it for a test drive and there no more slow acceleration etc, there is still hesitation at 2k rpm in 4th and 5th gear but i'm assuming that's the AFRs because of the LTI's and RTPs installed so i'll see if a tune sorts that out.

 

nice! your best bet is to go and do some logging of AFR. will tell you all you need to know.

anyone with over 150k miles on these is better of to just go and replace the pump as a maintenance/precautionary measure, as it will fail eventually.