FX45 hesitation/stumble between 3K and 4K in every gear

C

CBRworm

Member
Location
South Florida
Car
2012 FX50S
The title pretty much says it all. I noticed this first around 40K miles ago, it would happen if I put in non-ethanol 89 gas instead of 93 w/ethanol. The first time it happened I was on the interstate at around 3,400RPM and noticed that it felt slower than usual and saw that my gas mileage had dropped from the normal 15ish at that speed to around 10. I thought - headwind, and slowed down some. After that it kept stumbling through that range in any gear until I refilled the tank at my normal station and got 93. A few thousand miles later I got gas at a different station, but still 93 and the stumble came back. I changed the plugs which had 40K on them (this happened to be at 100K so I rolled it into a 100K service) and I swapped the new MAF from my G35 into the FX45 to see if maybe the MAF was having problems.

It seemed to run OK for a while, but sometimes the stumble would be there and sometimes not. Now at 120K (with the new MAF still in place) the stumble/surge is present almost all the time between 3K and 4K. The only other work done to the engine was I replaced the bottom crank position sensor at some point in the not too distant past with an new OE part due to a hard start/no start issue.

With the windows down as I am going through that range, I frequently hear what sounds like a single ping, or it could be a mechanical clank that happens at that RPM, I don't know what speed the intake runner butterflys change position. I also don't know if the cam phasers make any noise during operation at that point. I do know that my G35 pings a ridiculous amount (has since new) and it doesn't seem to pull enough timing to feel a difference.

Watching through a realtime scan tool, I don't see timing being pulled, but it does seem to be quite rich as reported by the wideband O2 sensors - I figure that may be normal for acceleration through that range.

Any ideas? Again, this happens in every gear at mid to WOT. I alternate between driving it like a grandma when my kids are with me to driving like a loon when they are not. I also tow a ~1,500-2,000 lb trailer with it for hundreds of miles on odd weekends.
 
The VK45DE is a high compression motor and should not be run with 89 octane 91 octane is the lowest grade you should run especially if towing or driving like a "loon"
If the problem is still persistent after running premium fuel check your plugs again cause you may have some signs of detonation or pre-ignition.
Also make sure your plugs are gaped properly and also try a throttle body cleaner and or seafoam in the intake and gas tank.
you can find videos on youtube of how to do the seafoam in the intake manifold properly.

I personally use a full bottle of 91% Isopropyl alcohol in a full tank of 93 octane once a month

And for anyone who rejects the isopropyl alcohol idea check all of your $6+ fuel system cleaner bottles the number 1 active ingredient is isopropyl so save some cash and go to CVS or Walgreens and buy a $1 bottle of rubbing alcohol
 
I also used isopropyl in my earlier days living in Wisconsin but we put it in to combine with any water that was in the fuel so its function was basically as a gas line anti freeze. I still use it in my boats fuel tank just to combine with any water in the tank, not as a gas line anti freeze.
 
Interested in this.... have similar problem, mine stumbles more in 3-5 gear however. 100K service done recently (early at 90k, have 101k now and had fuel lines all flushed and injectors checked to make sure spraying right at dealer), runnin synth oil, always premium, and fuel additive 1x month, and new intake filter as well. Problem is off and on for me but has never been present in first or second gear. Never tried WOT, mine is more mid-range throttle. Any additional input from other members would be great.

03 FX45
 
stupkat said:
Interested in this.... have similar problem, mine stumbles more in 3-5 gear however. 100K service done recently (early at 90k, have 101k now and had fuel lines all flushed and injectors checked to make sure spraying right at dealer), runnin synth oil, always premium, and fuel additive 1x month, and new intake filter as well. Problem is off and on for me but has never been present in first or second gear. Never tried WOT, mine is more mid-range throttle. Any additional input from other members would be great.

03 FX45
Click to expand...


Can you possibly elaborate on "stumble"
does the car hesitate to accelerate for a quick second?

do you see the rpm's rise but the car seems to not be accelerating?

is it lack of throttle response? or more like a misfire?

if it is a lack of throttle response you could try resetting the throttle open close position by cycling the ignition on off http://www.nicoclub.com/archives/g3...e-pedal-release-idle-air-volume-learning.html check this thread

Also for better throttle response clean your MAF sensor which is inline between your air filter and throttle body and also clean your throttle body with carb cleaner or MAF cleaner.

if it is a misfire usually a check engine light will be on with it and the code will help you pin point which cylinder is your problem

let me know if any of this helps
 
The car pulls fine up till then, then the power seems to drop off. The RPM are not jumping without accelleration, so i dont think the transmission is slipping. I had the techs at infiniti dealer go through and they checked for misfire when i did my 100k maintenance. They changed out the plugs as past owner had 2 different types of plugs in her. Right now the only code and CEL is for a bad cat, diagnosed by autozone on code and confirmed when infiniti went through tests of everything. (be puttin on HFC when i find a pair to swap directly in...input would be good)

I did top oil off last night to top of fill point, and put in a bottle of octane booster on top of my 91 octane, currently running good and didnt have any hesitation last night after this or this morning.
 
it is definitely an engine stumble. I typically only run 93 octane gas, but have run 89 no E a few times and I have replaced the MAF and plugs recently. The stumble feels like either a timing retard or mixture too rich, but only at that engine speed. There is no slipping of any sort.
 
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In my personal opinion i would check for a sticky egr valve as this will cause a stumble if its staying stuck open as your gasing up. Also if you have a scan tool available check your sensor data and check your baro sensor reading and map sensor reading. Newer cars baro is part of the map sensor. my readings here in boston ma for sea level are close to 14.7psia, 101kpa or 29.9 inches hg. In that range. Anything a few numbers abobe or below that can cause you stalling issues because if your readings are too low the computer will enrich your fuel mixture therefor making it run excesively rich or if too high it will run lean because theres alot less oxygen up in the mountains. I recently had a car that had a stalling issue. And come to find out my map sensor was way off the charts at 4,000 feet below sea level and throwing too much fuel at it. But if your gona check those check with your local airport to find out what your local sea level readings are. They have the best answer. Good luck!
 
Yeah, I have monitored scan tool data real time and have not seen anything out of line, other than it seems to go rich through that range - which might be normal. This motor does not have EGR as far as I know, I understand it is done via variable cam timing.
 
I've been experiencing similar issues...a loss of power/hesitation when stepping on it at the beginning of 1 & 2 gear around 4k rpm. This post gave me some good insight on the on the issue thanks guys.
 
I finally figured out what this was.

On my FX45, the vacuum line that goes from the vacuum switching valve to the actuator on the back of the intake manifold had split, so instead of changing intake runner length, it was creating a vacuum leak and keeping the runners short. So, double whammy.

No codes were set, I found this when I removed the plastic cover to look at something else.
 
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