My 07 G35 sport sedan after having the ac compressor and new belt replaced (after battery was disconnected for a day or so) The car started a pretty big hesitation when taking off from a stop when you lightly accelerate.
I read where guys said to disconnect battery again and some times it fixed it. I did that, and it was gone completely until the car comes up to operating temp and then it was back. I then saw one guy say he had to replace the battery and I tested mine and it was going bad, so I installed new interstate battery and I thought it was fixed over several days it seemed to be gone. Then it came back again, but its very slight and only when taking off from a stop after the operating temp is up to normal and only under slow take off. If I give it more gas from a stop no hesitation, and it does not miss a beat driving and stepping on it, no miss. I cant figure it out. I also then put new plugs in it, but same issue. Has right at 108k now.
I saw guys talking about reflash, and some saying there is a procedure I can do using the gas pedal etc, does anybody know the exact directions to do that as I want to give it a try before driving 2 hours to Infiniti as not sure what else to do myself.

 

Definitely look around for any small vacuum leaks first since they will also cause a hesitation, the 2007-2008 HR was pretty notorious for a slight hesitation that could be corrected with the newer reflash though.

 

Thanks on the vac leak it does not hesitate at all when operating temp is below half and it all started after battery disconnect and new ac comp install, so I keep thinking its not vac leak that is has to do with the ecu possibly?
When you say newer flash, do you have steps for that?

 

It's not something you can do yourself, requires the dealership Consult-II / III tool.

 

Ok thank you, can I do it with a certain scan tool, I have a Foxwell for my BMW's and I think I can add the software for Infiniti.

 

No, unfortunately it's a dealership specific tool.

If the ECM update is the issue I'm betting it could be fixed with an Uprev tune as well though, I bet @seymore4 would know.

Definitely check for other potential issues though, starting with vacuum leaks, spark plugs, etc. Also if you have access to a realtime OBD2 scanner watch the O2 sensor to see if it's just getting old and lazy, doubt this is the problem though.

Also check for hidden codes, you might be throwing one, not all codes will trigger the check engine light.

 

This is an interesting one. 2007 sedan came with the VQ35HR right?

 

Yes, I've heard of this issue quite a bit and it's usually resolved by having the dealership reflash the ECM.

 

Tune fixes everything! 😅

 

I'm having this exact same issue with my 2008 G35X. I bought the Z1 high energy coil packs and good sorry plugs and it did run really well for the most part except it still has the stutter after getting up to temp! I still need to check for vacuum leaks but this is driving me crazy! I recently purchased the XTool A30M just cuz and it is showing a code for O2 sensors bank 1 and 2.. the Xtool shows no voltage to both down pipe sensors. I ordered some from rock app that should be here later this week and we'll see what they can do for me.

 

OP, can you describe the hesitation? does it feel like it's about to die (rpm dip) during that slow takeoff? mine had a similar issue that turned out to be a weak fuel pump. check your afr with torque or some other obd2 app when you gun it. it should dip down into 11s/12s at most at high load. if you're anywhere near 13 or more, your pump is on its way out. this is very hard to diagnose w/o having any codes on the dash.

 

Mine is exactly like your description.
which sensor should I be looking at exactly? There's a couple that say "Air Fuel sensor"
I've attached a snapshot of all the readings I could get from Xtool

 

I see several Air/Fuel indicators in that pdf. Torque is very simple in that regard. You can just choose to display the AFR in real time, without having to look at the voltage and figure out what your AFR is.

Scan Data Analysis section here describes how you can use those xtool indicators. Hopefully i'm not sending you on a wild goose chase here, but it's worth testing your fuel pump to make sure it's operating as it should.

Understanding Nissan's wide range oxygen sensors | Vehicle Service Pros

 

Those O2 heater codes shouldn't be causing a hesitation.

 

update: I replaced the fuel pump assembly with this Hitachi from Rock Auto. https://www.rockauto.com/en/moreinfo...=10147&jsn=360
It's running exactly the same except that the O2 codes I had before have gone away on their own. This also happened a week ago just coming home from work after the CEL starting flashing then solid again.. no noticable driving concerns and I already had the OBD2 plugged in so i checked it quick after and it showd a cylinder misfire??? never had that before but I didnt feel anything knocking or shaking (i think i know what a misfire feels like since my 03 maxima is having an 'actual' cylinder 3 misfire... shaking engine harder with rpms as they go up etc..) The G was fine driving and then the CEL went away entirely and i ran the codes again and it indeed showed no codes.. for a couple days and the same O2 codes came back...
All that to say this,
After replacing the fuel pump it runs exactly the same. stuttering at parkng lot speeds when I rev to about 1000rpms just barely pushing the throttle from a stop. Only when its under a load like Drive or Reverse will it stutter the engine. Park and Neutral the engine revs smooth all the way up. I have still not checked for vaccuum leaks and if anybody has the best method, I would appreciate that info. Listening for leaks is difficult cuz trombone exhaust ya know? I can share some OBD scans if anybody understands it like that.