My city MPG can drop to 10mpg, but often averages 12. Highway is 19-20, which is normal. Does any of you FX45/50 owners get better gas mileage around town?

I have no check engine lights "on" and other than 115,000 miles on the OEM O2 Sensors, I'm considering the possibility of replacing my 2 "upstream" O2 sensors. I'm also thinking O2 Sensors are the next step to improving city mpg if I have already performed a Seafoam treatment and cleaned my MAF sensor. So what do you think? And why do so many sensor vary in price?

I'm also concerned these cheap O2 sensors on Amazon may prematurely fail so I want to stick with Denso, Bosch or NTK/NGK, but if anyone has used the Walker or other Ebay vendor brands, please let me know if you are satisfied and if your mpg or performance improved after you replaced your sensors.

At O'reilly's these name brand sensors run $80-$120 each and since there are 2-upstream and 2-downstream sensors that's a lot of clams. So I'm thinking of only replacing the upstream if I am trying to improve my city mpg vs. trying to pass an emissions test. ...And remember I don't have any sensor codes flashed on my OBD2 Scanner.

So before I start throwing more money at this problem I'm hoping there are some testimonials out there to guide my decision. And I full accept most mechanics will say to do nothing until you get a TDC. However, I also know all O2 sensors degrade over time for a lot of reasons. And frankly, it's easier to just replace them vs. test them.

Does anyone know what the OEM brand of sensors Infiniti uses?

Attached is a chart I created with extra information on this subjeck with some part numbers... for your library.

imnprsd wrote: ↑

Sat Mar 12, 2022 2:09 pm

And I full accept most mechanics will say to do nothing until you get a TDC. However, I also know all O2 sensors degrade over time for a lot of reasons. And frankly, it's easier to just replace them vs. test them.

Unless they're easy to reach with a tap and thread chaser, I'd think twice about changing them prophylactically. The other thing they do besides degrading over time is seize in the hole and butch the threads on the way out.

VStar650CL: I appreciate your reply. Do you know if the Infinti exhaust "bung" is prone to corrosion or if your comments are good advice in general?

Likewise, if I do remove the old O2 sensors I will use some "Corrosion Buster" spray the night before, if I do this job at all. (TBD) Hopefully, someone with an FX45 can give me the benefit of their efforts and results before I go for it.

Note: I found 4 different Bosch O2 sensors on Ebay, from the same seller/store, for only $21 each (x4), but he has not confirmed Bosch is the manufacture and are in the original box and a branded "Bosch" on the part. So I'm waiting for that information before I order. I.e., for $42 to replace the "upstream" O2 sensors with a Bosch brand I may try it and see what I get. However, when O'relly's charges $200 for 2 sensors I'm not so inclined to go fishing when I don't have a TDC light flashing.

Can anyone tell me why I need to replace the 2 "downstream" sensors if the purpose of this effort is to improve city mpg?

Note: My engine runs great and starts up right away!

imnprsd wrote: ↑

Mon Mar 14, 2022 7:30 pm

VStar650CL: I appreciate your reply. Do you know if the Infinti exhaust "bung" is prone to corrosion or if your comments are good advice in general?

Likewise, if I do remove the old O2 sensors I will use some "Corrosion Buster" spray the night before, if I do this job at all. (TBD) Hopefully, someone with an FX45 can give me the benefit of their efforts and results before I go for it.

They all seize, and on a ride that old, no amount of PB Blaster is likely to help.

imnprsd wrote: ↑

Mon Mar 14, 2022 7:30 pm

Note: I found 4 different Bosch O2 sensors on Ebay, from the same seller/store, for only $21 each (x4), but he has not confirmed Bosch is the manufacture and are in the original box and a branded "Bosch" on the part. So I'm waiting for that information before I order. I.e., for $42 to replace the "upstream" O2 sensors with a Bosch brand I may try it and see what I get. However, when O'relly's charges $200 for 2 sensors I'm not so inclined to go fishing when I don't have a TDC light flashing.

Personally, my customers who tried Bosch have virtually all been sorry. If you can't afford OE, get Denso. Good ones will not be $21.

imnprsd wrote: ↑

Mon Mar 14, 2022 7:30 pm

Can anyone tell me why I need to replace the 2 "downstream" sensors if the purpose of this effort is to improve city mpg?

The downstream sensors will most likely do nothing for you. They're there to monitor the front cats, the ECM does not use or evaluate them for running the engine. Our saying in the business is, "The front O2's are for the engine, the rear O2's are for the government."

VStar650CL: Thank you for sharing your experiences with us. And clarifying your position on Bosch.

When/If I do replace the 2 front O2 sensors I will post the results.

Question: I would think my Hwy AND my City MPG would both be affected by a bad or "weak" O2 sensor. However, in my case, my 2004 FX45 is getting 19-20 MPG on the highway. So does this suggest replacing the front O2 sensors are not necessary? ...And I just have to accept the around town city MPG is normal at 10-12 MPG?

...Again, my engine is really running great in all other respects.

I just came across this Fuel Trim Relearn Procedure and will try it. However, I don't know what to expect. I just know it can't hurt. After which I will monitor my city MPG to see if it has any positive affect:

https://www.infinitihelp.com/diy/fx/pro ... arning.php

Mixture Ratio Self-Learning Control Procedure

Instructions
1) Start engine and warm it up to normal operating temperature.
2) Turn ignition switch OFF.
3) Disconnect mass air flow sensor harness connector, and restart and run engine for at least 3 seconds at idle speed.
4) Stop engine and reconnect mass air flow sensor harness connector.
5) Make sure Detected Trouble Code (DTC) P0102 is displayed.
6) Erase the DTC memory.
7) Make sure no codes are stored in the ECM.
8) Run engine for at least 10 minutes at idle speed.

Has anyone heard of this? ...Does it work? Is if used to cure rough idle conditions or is this for MPG improvement?

Some DTC's, including most MAF codes, will make the ECM discard the long term fuel trim data. It isn't well-documented which cars and which codes it will work for. Most good scanners, including Torque Pro for your phone, have LTFT clearing available as a work support item. That's obviously a more reliable method. The first thing you or anyone should do when a fuel mileage problem is suspected is an Idle Air Volume Learn (IAVL) after cleaning the MAF. That's also a work support item. The silicon in a MAF can experience quite a lot of component drift over time if it never gets recalibrated. I've personally seen one that was off nearly 30%.

You help lead me to do some more research and and found a number of forum threads that have a lot to do with how the ECM sensors communicate with several sensors to determine the most optimal fuel trim.

Below is a summary of several easy to do procedures to keep your 2003-2012 FX45/FX35 operating at peak performance.

2003-12 FX45/35 ECM IDLE AIR RELEARN + THROTTLE RELEARN + MAF RELEARN NOTES (with edits)
("2003-2012 Infiniti FX35 - FX45)

Before performing Idle Air Volume Learning Procedure, make sure that all of the following conditions are satisfied. Learning will be cancelled if any of the following conditions are missed for even a moment.

The first 2 procedures are done with a cold engine and only take 2 minutes. (EASY-PEASY!) The next 2 procedures are done with a hot/normal engine and are also easy to do if you have a OBD2 Scanner that lets you reset your Trouble Detection Codes (TDC). Here’s and Amazon link to $23 Scanner I used:

https://www.amazon.com/gp/product/B07YH ... UTF8&psc=1

Perform Accelerator Pedal Released Position Learning (Cold Engine)

Note: This must be performed each time harness connector of accelerator pedal position sensor or Engine Control Module (ECM) is disconnected.

https://www.infinitihelp.com/diy/fx/pro ... arning.php


1) Make sure that accelerator pedal is fully released.

2) Turn ignition switch ON and wait at least 2 seconds.

3) Turn ignition switch OFF and wait at least 10 seconds.

4) Turn ignition switch ON and wait at least 2 seconds.

5) Turn ignition switch OFF and wait at least 10 seconds.


Perform Throttle Valve Closed Position Learning (Cold Engine)

https://www.infinitihelp.com/diy/fx/pro ... arning.php

1) Make sure that accelerator pedal is fully released.

2) Turn ignition switch ON, but do not start engine.

3) Turn ignition switch OFF and wait at least 10 seconds

==> Confirm the throttle valve moves during above 10 seconds by

confirming the operating sound. If not then proceed...

4. Turn ignition switch “ON” (without starting vehicle) and wait at least 2 seconds.

5. Turn ignition switch “OFF” wait at least 10 seconds.


END



Idle Air Volume Relearn Procedure To Reset ECM (Hot Engine)

Complaint: I cleaned my throttle body last night and now my truck idles a tad higher. Also the C.E.L. is on.

RESPONSE: This problem is perfectly normal after cleaning/replacing the throttle body. To fix it just perform this Idle Air Volume Relearn Procedure.


https://www.infinitihelp.com/diy/fx/pro ... arning.php


1) Start engine and warm it up to normal operating temperatures by driving the car for 10-15 minutes.

2) Check that all items listed below are in good order:

* Battery voltage: With engine running, alternator is putting-out +12.9V- 14V.

* Engine coolant temperature: 70 - 100 C (158 - 212 F)

* Park/neutral position (PNP) switch: ON (Shifter in Park or Neutral)

* Electric load switches “OFF.” Ex: Air conditioner, headlamp, rear window defogger, seat heaters.

* Steering wheel: Neutral (Straight-ahead position)

* Vehicle Cruise: OFF/Stopped

3) Turn ignition switch OFF and wait at least 10 seconds.

4) Confirm that accelerator pedal is fully released, turn ignition switch ON and wait 3 seconds.

5) Quickly depress the accelerator pedal 5 times within 5 seconds. (Aka “Stomp Test.”)

6) Wait 7-10 seconds, fully depress the accelerator pedal… and keep it depressed for approx. 20 seconds until the MIL (Check Engine Light) stops blinking and turnes ON.

7) Fully release the accelerator pedal within 3 seconds after the MIL (aka CEL) turned ON.

8) Start engine and let it idle.

8) Wait 20 seconds.

9) Rev up the engine two or three times and make sure that idle speed and ignition timing are within the specifications. Note: Your idle speed = 650 ± 50 rpm (in P or N position)

END


NOTES: If the above 8 steps do not turn on the CEL as described, try this sequence commonly used on Nissan Pathfinders to accomplished the desired results:


----- EASY METHOD TO RESET ECU ON NISSAN 2005 PATHFINER -----

1. Ignition "ON", count to 3 (1000-1, 1000-2, 1000-3)

2. Depress/Release pedal 5 times...hard and fast within 5 seconds.

3. Count to 10 (not 7!) and fully depress pedal

4. Count to 12 (WIF Light should be blinking and then will turn “solid-on.” When it does turn “solid-on” release pedal.

5. Count to 10, depress pedal

6. Count to 10, release pedal.

7. Turn Key off.

END.



NEXT PROCEDURE… And for added measure do this to reset how the Mass Air Flow (MAF) sensor communicates with the ECM.


MAF Sensor / Fuel Trim Relearn Procedure (Hot engine)

https://www.infinitihelp.com/diy/fx/pro ... arning.php


1) Start engine and warm it up to normal operating temperature.

2) Turn ignition switch OFF.

3) Disconnect mass air flow sensor harness connector, and restart and run engine for at least 3 seconds at idle speed.

4) Stop engine and reconnect mass air flow sensor harness connector.

5) Make sure Detected Trouble Code (DTC) P0102 is displayed.

6) Erase the DTC memory.

7) Make sure no codes are stored in the ECM.

8) Run engine for at least 10 minutes at idle speed.

END.

With my $23 OBD2 Scanner I was able to perform the MAF sensor relearn steps above and now my idle is holding right at 650RPM. (Before the engine would idle high in the the morning and then average 750RPM after the engine heated-up.)

The OBD2 scan tool also reveled the information below to me... and based on this data (at idle) I don't plan on replacing my O2 Sensors unless someone says I need to replace them? Note: I'm out of school on this subject so I would appreciate more discussion on this subject. However, at idle I think if the voltage remains at all times below 1V then the sensor is okay. Is this true or is it more likely I have to increase the RPM to ~1,800 and then take measurements?

UPSTREAM SENSORS AT IDLE

B1S1 Voltage would oscillate between 0.07V - 0.73V (occasional 0.90V) and held relatively steady at 3.9%-4.7%
B2S1 Voltage would oscillate between 0.04V - 0.45V and held relatively steady at 3.1%-4.7%

DOWNSTREAM SENSORS AT IDLE/b]

B2S1 would oscillate between 0.06V - 0.18V and held relatively steady at 3.1%-4.7%, with SHRTFT= 99.2%
B2S2 would oscillate between 0.45V - 0.46V (is this okay?) and held relatively steady at 3.1%-4.7%, with SHRTFT = 99.2%

Notes: I'm not getting any TDCs. My complaint is that my city MPG seem very low at 10MPG. However, after performing the above relearn steps, I think my dash data computer that measures MPG is reading in the 14-16 City-MPG so long as it is not stop-and-go traffic. So maybe I'm seeing some improvement. It's too soon to tell.

Your ride has 1.5V type A/F sensors (front O2's). They're direct-acting, above 1.50V the mixture is lean, below 1.50V it's rich. Nissan engines will always run a trifle rich at idle to keep the engine speed steady and smooth, so you can't tell much about the readings until you're cruising. Since your STFT is right around 100% on both banks, I'd say your engine and fuel system are fine.

The A/F's are for the ECM, the rear O2's are for the EPA. Contrary to urban mythology, the ECM does not use the rear sensors to run the engine in any way. The whole job of the downstream sensors is to make sure the catalytic converters are doing their job. The oscillations seen in the rears when cruising with lit cats are not a function of the sensors themselves, it's from the ECM deliberately cycling the engine rich-lean to watch how the cat responds. So forget watching the rears to learn anything about your engine, that isn't how it works.

VStar650CL: Once again, thank you for making sense of data most of us do not understand.

I will continue to monitor my city MPG and report back if the ECM "Relearn" steps as described above move the needle from 10MPG-City to more like 14+MPG-City. TBD.

OP UPDATE: After performing all of the engine "relearn" steps which I hoped would improve my city MPG... it did not! And I am still getting 8-10MPG in stop-and-go traffic. Is this normal?

I get that if you are just waiting at a traffic light... that your MPG will be crappy.... because you are not moving... but I'm still surprised a rich running engine would "draw-down" my overall MPG numbers this much.

So then... other than replacing my 2 "upstream" O2 sensors "on a lark," I have no other ideas on how to improve my city-MPG. So what am I missing?

Note: I am aware, in general, O2 sensors wear-down over 100,000 miles and my car has 117,000 miles and my engine is not flashing any TDC. So that begs a question when my city-MPG is low: Are my "upstream" O2 sensors good or not?

Note: I am still getting 19-20 MPG on the highway, which is good, However, I'm still having trouble accepting this V-8 has normal fuel trims when I'm only getting 10.7 MPG overall. ...And yes, 80% of my driving is around town.

Maybe the question I should ask is this: What is your FX45 city and hwy MPG?

I hate to be the bearer of bad news, but that 10.7 isn't terrible for a 4300 lb car if you're coming off stoplights 80% of the time. The EPA figures on the FX were only 15/19, and EPA's "city" cycle is notoriously kind. Nobody ever matches it except Grandma Moses on a Green Light day. You're hitting the highway figure, so there's nothing wrong with your state of tune. You're just driving a big chunk of iron.

If my Highway-MGP is 20-22, why is my engine so rich at idle? ...And is there any thing that can be done to to fool the ECM so I can get better City-MPG?

Has anyone "chipped" there engine? Cam this even be done?

I have used these ECM "Fooler" chips in other engines got better MPG and more HP, but so long as you have a "light-foot" you can't get in any trouble; and along the way your MPG is better.

I also am stll not satisfied with 8 MPG in heavy Stop & Go city traffic! IMO, this is ridiculous even for a V8!

FYI, I have not replaced my O2 Upstream Sensors... yet. But I'm sill shocked my engine idles so rich! ...So much so, I can't believe it was designed this way????

Note: I have also checked my engine FUEL EVAC SYSTEM components and all is normal. So why did Nissan make an engine that runs so rich at idle? ...So hunk or medal or not, Kg or Lbs, at idle this is not a factor. Also, when the car is rolling without frequent idle-stops the City MPG can be in the 13 range. I.e., my engine at idle is a real PIG I want to slaughter if I can't fix it.

==> And my spark plugs are a nice gray color so its not showing fuel delivery problems. So again, I conclude, it's not the weight of the vehicle. It's the idle mixture that is the problem. So how can we fix that?

There are no plug-in "chips" like you'd put into, say, an old Fox Body 'Stang, but there may be a tuning package available for your ECM. I don't get into that end of things very much as a dealer tech, so maybe someone else can chime in who knows more.

One thing you may not have checked which might compromise your mileage is the IAT sensor, if that's reading colder than it should then the ECM will be enriching more than necessary. Even if it's healthy, you can actually "fool" the ECM into leaning the mixture by putting a parallel resistance to ground on the IAT circuit, making the ECM think the incoming air is warmer than it really is. You just need to be careful about overdoing that, it can result in a crappy idle, off-idle hesitation, and prematurely burned-up spark plugs.

Vstar650CL: Thank you for sharing. I think you might be on to something which all us FX45 owners have paid no attention to for years.

The other day I decided to check my spark plugs for several reasons and I can now share the following:

1) I wanted to make sure the spark plug tube seals in the valve covers were still sealing oil out. I did this because my valve cover gaskets on both side just started to leak oil and it's about $600 to replace V8 valve covers (both sides) vs $200 to replace a V6 valve cover. (This is a separate discussion.)

The short story for me is that all my spark plugs tube are dry and I was able to put 1/8" turn on most of 10mm valve cover bolts so I'm hopeful that will stop the oil leak; and I use some "Blue Devil" Stop Oil Leak, which I have had good success with in the past.

2) I replaced my stock NGK Spark Plugs (LFR5A-11) with Denso Iridium (SK16HR11) which are the same heat range. And even though my old plugs really showed signs of wear, the new plugs did not improve city-MPG. On the other hand, my engine sounds smoother and the engine is very quick to react to small throttle changes... like it is supposed to do.

3) I cleaned the throttle body using MAF Sensor cleaner, which was not that dirty; and when it came to doing the Throttle Relearn procedures, and resetting the MAF sensor fuel trims, by first disconnecting the MAF and clearing the codes using my code reader , this time I also noticed a P0113 IAF code as referred to above.

==> So I googled this P0113 code and learned the IAF sensor is part of the MAF, and then there is this:

https://www.engine-codes.com/p0113_infiniti.html

The Intake Air Temperature (IAT) sensor is built into mass air flow sensor or in some vehicles mounted to the air filter duct housing.
The sensor detects intake air temperature and transmits a signal to the Engine Control Module (ECM). The temperature sensing unit uses a thermistor which is sensitive to the change in temperature.
Electrical resistance of the thermistor decreases in response to the temperature rise. The Intake Air Temperature signal is used as an input for various systems in the vehicle.

===

That said, Vstar650CL, are you saying we can add a parallel ground wire (with some resistor value in the circuit), that will increases the total resistance value as seen by the ECM? And if so, will this fool the ECM into thinking the air temperature is warmer? ...And the net affects are that the idle AF mixture will create a leaner running engine at idle? ...Without affecting highway fuel mixtures? ...Have I got these relationships right?

And if so, do you know which MAF color
wire I should target and what R-value I should use? (See attached picture.)

Why am I motivated to do this? Well, about 80% of my driving is in the city and driving this FX45 around town when it's only getting 8MPG is rather expensive!

PS
I'm not worried about the lean mixture at idle, because I know my FX45 engine runs rich and is setup for higher performance at the sacrifice of poor city-MPG and high fuel mixtures at idle.

That said, I think the fuel trim settings from the factory is not the greatest for city driving; which begs the question: Can the OEM ECM fuel trims be changed with the Infiniti Insite System at the dealer?

imnprsd wrote: ↑

Mon Sep 19, 2022 6:54 pm

That said, Vstar650CL, are you saying we can add a parallel ground wire (with some resistor value in the circuit), that will increases the total resistance value as seen by the ECM? And if so, will this fool the ECM into thinking the air temperature is warmer? ...And the net affects are that the idle AF mixture will create a leaner running engine at idle? ...Without affecting highway fuel mixtures? ...Have I got these relationships right?

Not quite. The sensor will be NTC using a fixed pullup inside the ECM, so the resistance will drop as temperature increases, and because the fixed element is biased to 5V and not ground, the voltage will also fall and not rise as the temperature rises. To "fool" the ECM a trifle lean will mean raising the apparent temperature, so a parallel pull-down will do it.

imnprsd wrote: ↑

Mon Sep 19, 2022 6:54 pm

And if so, do you know which MAF color
wire I should target and what R-value I should use?

No, but the FSM knows. There may be an RT (resistance:temperature) chart, but if not, a pair of resistance readings at two accurate temperatures will allow determining the sensor beta, then a little algebra will come up with a likely value.

imnprsd wrote: ↑

Mon Sep 19, 2022 6:54 pm

I'm not worried about the lean mixture at idle, because I know my FX45 engine runs rich and is setup for higher performance at the sacrifice of poor city-MPG and high fuel mixtures at idle.

It doesn't work that way. Tweaking the IAT will affect the mixture across the range.

imnprsd wrote: ↑

Mon Sep 19, 2022 6:54 pm

That said, I think the fuel trim settings from the factory is not the greatest for city driving; which begs the question: Can the OEM ECM fuel trims be changed with the Infiniti Insite System at the dealer?

No. The map can only be tinkered by way of a tuner. Consult3+ doesn't have the ability to change the target mixture.

Thanks VStar650CL for your follow-up answers. I'm not at your technical level, but I can follow your comments. I'm just too stubborn to think there is no solution to improving city-mpg. I mean, why would any engine manufacture enrich the misture so much that it would only get 6-8 MPG in the city back in 2004?

I also suspected the ECM is simple device. I first thought that maybe my EVAP system was messing with the city-MPG, but found this was not the case. I.e., it purely is the way Infiniti set the fuel trims at idle. ...But why?

I know the idle is more stable with a rich mixture, but I can litterily see my city-MPG drop from 15MPG when I'm driving to 6-8 MPG when I come to a stop... again-and-again.

And if the spark plugs are "black" due to idle air-fuel-mixture setting then why would Infiniti do this?

The only answer I can come up with is this: Back in 2004 "performance" sold cars and they optimized this beast for g-forces. And being an old motor-head, I do like those G's!

...But now that we are paying over $5/gal, and becuase I drive 80% of the time in the city, I'm more interested in good city-MPG. So whatelse can I do to fool the ECM without affecting my highway-MPG? Nothing?

... Is there a vacuum hose I can plug? Haha! ...No seriously. ...Is there a vacuum hose I can plug?

...What does that vacuum hose do (or go to) that drapes over the air snorkel in the above picture?

...And what does the plastic looking thing, that is to the left of the snorkel do?

imnprsd wrote: ↑

Mon Sep 19, 2022 9:44 pm

... Is there a vacuum hose I can plug? Haha! ...No seriously. ...Is there a vacuum hose I can plug?

...What does that vacuum hose do (or go to) that drapes over the air snorkel in the above picture?

...And what does the plastic looking thing, that is to the left of the snorkel do?

I must say, you make me seriously reminiscent for Mythbusters. I keep hearing Adam say, "I reject your reality and substitute my own!"

The plastic bubble is a tuned resonator which prevents "howl" and harmonic logjams in the intake at certain RPM's. The hose is ported vacuum for the intake manifold runner (power valve), which Nissan calls VIAS. You can read all about it on EC-1276 here:
https://www.nicoclub.com/service-manual ... 5%2Fec.pdf

Thanks. I try to make things entertaining if not informative. And you are right. I do like to push the envelope, and when I get lucky, I sometimes come up with a better mouse trap. But to do that I need help from the professionals. And this is one of those times. So again thanks for everyone's help noodling on this: Why is my Highway MPG in spec, but my City-MPG so horrible?

First I considered a vacuum leak, but none was found. Then I checked the VIAS solenoid and found that was not the problem. Then I since I needed to replace the spark plugs at 115,000 miles I decided to to with the same heat range, based on the color of my old plugs, only I selected the Denso Irridium type, and I think these are the better way to go at this point.

And least I forget, I found the new MAF sensor did improve the engine response, but I am still looking at 6-8 MPG in the city. And in very congested city traffic I would clock 4 MPG on the Infiniti Fuel Economy gauge over several 1 mile, 2 mile and 3 mile test cases.

So being the myth buster that I am, I am wondering if that other, vary rare symptom I experienced a few months back has any thing to do with my poor City-MPG? That problem was this: My engine would 99% of the time start on the first key turn, but sometimes I had to try 2 or 3 times by turning the key to "off" position and try again.
Note: This condition went away when I cleaned all the fuses in the fuse block next to my left knee inside the car vs. my Infiniti dealer who told me I need a new starter. However, other owners who live in freezing weather reported their No-Start Key Problem got fixed by replacing that blasted Air Conditioning (AC) Amplifier under the radio, which ties into the security system, and which can probably fixed with a solder iron by reflowing a x “cold” or cracked solder joint inside the AC-Amplifier. ...But I digress.

My point is this: All these FX45 engine sensors use a "Hall Effect" sensor type to regulate the engine, which in my case, IMO, at idle produces the weakest field possible. And while there is no CEL to pin point which sensor may be weak, it does beg the question: which one or multiple sensors might you replace first? ...Considering the problem here is too rich of a mixture at idle. And since I am NOT having a no-start problem, and no CEL then I believe only a weak sensor would be at fault; if this is even the case?

And/or it could be my upstream O2 sensors should be replaced, but again, my idle RPM is good and the throttle relearn also worked fine, and now my RPM holds steady at 650RPM.

I think for my money, I would not go about replacing all the sensors, even if there are some cheap ones on Amazon with good reviews. However, because there is only one (phase) sensor, which would affect both engine banks equally, then maybe that is the sensor I would start with and replace. I.e., if all the other sensors control Cam #1 timing and Cam #2 timing, and since my engine is running smoothly and has great power, then these sensors probably are not suspect.

What do you think? Can a fulling functioning, albeit weak, Cam Shaft (Phase) Position Sensor cause a rich AF mixture at idle, at a full stop? ...And BTW, I think this single sensor is better described as a Crankshaft Position Sensor, but I'm not sure on that?

This sensor is the single sensor I highlighed (in green) in the diagram below. Infiniti Part# 23731-4M506, which is now # 23731-4M50D (or at O’Reily’s they sell an Import Direct# 19-0205 for $40) worth replacing?

...An I wonder how easy or hard is is to get to?

I'd start with the crank. Cams are relatively slow moving and have more metal between teeth than the crank, so they're less susceptible to electrical noise. They're also more angle-critical, but still, a CKP can need to output 700Hz even at idle. Cam sensors output no more than 250Hz even at redline. Reluctance increases with the speed of the reluctor, and since your issue is at the bottom, if a sensor is causing it then I'd suspect the crank first. Not saying I think it will help your mpg, I don't, but it certainly might be responsible for your intermittent long cranks.

Got it. 2 cams means I have 2 Cam Shaft Position Sensors. And 1 Crank means I have 1 Crank Position Sensor (CKP). I wish Nissan/Infiniti would not try to rename the obvious. As for the 2 oil pressure controled "solenoid" sensors, I don't see how these would factor into my assumptons regarding AF mixture at idle, and on top of that my idle is not rough or fast. So these mechanical "muscle part dubbed a Solenoid" must do all the work to vary the valve timing using oil pressure to move the valve timing mechanically. Am I right?

I think the ECM reads cam sensors and the CKP sensors and maybe the O2 sensors and then tells those solenoids to mechanically move the valve timing on each bank. Just a guess.

Consequently, I'm also guessing, the only other sensor left by deduction is that CKP sensor, which Infiniti calls a Camshaft Position Sensor for some reason? No matter. I ordered this $25 Beck Arnley Part # 180-0397 aka "Engine Camshaft Sensor" on Amazon and I will give it go and report back in a week or so.

https://www.amazon.com/gp/product/B002I ... UTF8&psc=1

I also noticed another owner in the Amazon reviews of this part said his MPG returned to normal after replacing this sensor. TBD. IMO, there are "long-odds" that I will see any improvement in MPG, but we shall see. ...And I have not rulled out replacing those upstream O2 sensors if this CKP R&R does not improve my city-MPG.

I also don't mind replacing a $25 CKP sensor as a "preventative maintenance" move -- if nothing else to avoid a tow down the road. My only hesitation is using sensors bought on Amazon, but I have had good success using the Beck Arnley brand -- so we shall see.

** Before anyone orders sensors for their engine, they should verify what the correct Infinit part number is for their engine first. There is a lot of confusion concerning sensor types and part numbers so do your homework. I use this website to look up Infiniti OEM part numbers:

https://www.infinitipartsdeal.com/parts ... m=130_B002

imnprsd wrote: ↑

Tue Sep 20, 2022 10:39 pm

Got it. 2 cams means I have 2 Cam Shaft Position Sensors. And 1 Crank means I have 1 Crank Position Sensor (CKP). I wish Nissan/Infiniti would not try to rename the obvious. As for the 2 oil pressure controled "solenoid" sensors, I don't see how these would factor into my assumptons regarding AF mixture at idle, and on top of that my idle is not rough or fast. So these mechanical "muscle part dubbed a Solenoid" must do all the work to vary the valve timing using oil pressure to move the valve timing mechanically. Am I right?

Yes. There's a part called a "phaser" on the end of each intake cam which responds to hydraulic pressure from the solenoid by advancing the cam angle. The ECM uses this in what's called "Miller cycling", manipulating cam overlap to inhale a tiny bit of exhaust gas between strokes. This eliminates the need for a separate EGR Valve to reduce NOx emissions. It's really a quite-elegant setup (elegant in the engineering sense).

imnprsd wrote: ↑

Tue Sep 20, 2022 10:39 pm

I think the ECM reads cam sensors and the CKP sensors and maybe the O2 sensors and then tells those solenoids to mechanically move the valve timing on each bank. Just a guess.

Very oversimplified and you're leaving out a raft of other sensors, but yes.

imnprsd wrote: ↑

Tue Sep 20, 2022 10:39 pm

Consequently, I'm also guessing, the only other sensor left by deduction is that CKP sensor, which Infiniti calls a Camshaft Position Sensor for some reason? No matter. I ordered this $25 Beck Arnley Part # 180-0397 aka "Engine Camshaft Sensor" on Amazon and I will give it go and report back in a week or so.

It's very common for a CMP on one engine to be used as a CKP on a different engine, or vice versa. So that's at least forgivable, unlike some of the weirder s*** Nissan does with part nomenclature.

imnprsd wrote: ↑

Tue Sep 20, 2022 10:39 pm

https://www.amazon.com/gp/product/B002I ... UTF8&psc=1
I also noticed another owner in the Amazon reviews of this part said his MPG returned to normal after replacing this sensor. TBD. IMO, there are "long-odds" that I will see any improvement in MPG, but we shall see. ...And I have not rulled out replacing those upstream O2 sensors if this CKP R&R does not improve my city-MPG.

I also don't mind replacing a $25 CKP sensor as a "preventative maintenance" move -- if nothing else to avoid a tow down the road. My only hesitation is using sensors bought on Amazon, but I have had good success using the Beck Arnley brand -- so we shall see.

I'm not a big fan of aftermarket Hall sensors on general. I've seen lots of hair pulled out over the years by well-meaning DIYers over them. China-cheap sensors are particularly prone, but never lose track of this fact -- magnetism is invisible. When it pulls your leg, you won't know about it.

UPDATE: Throttle Relearn Steps that are easier to follow and may cure your CEL Code #P0507 (High Idle).

These steps should work on your Nissan or Infiniti.

Follow these throttle relearn steps exactly as written below:

===> Turn off all loads like the AC and lights and other accessories if any.

1. With a cold engine..
2. Make sure the front wheels are straight ahead and everything is off, I.e. Radio, lights, wipers, heater, etc.
3. Shut the engine off, waited 10 secs. This resets the butterfly-closed position.
4. Turn the key to on, waited 2-3 secs
5. Turned the key to off, waited 10 secs. This resets the butterfly-open position.
6. Turned the key to on, waited 2-3 secs

===> Drive the car sufficiently to reach normal operating temperatures. Park it, and keep the front wheels straight ahead, loads off... and follow these steps:

Note: If you don't see your CEL blink in Step #3 below, then you will need to repeat these steps and pay closer attention the time as counted down on the stop watch.

1. With enging running, turn the key-off and wait 10-15 secs.
2. Turned the key-on, start a stopwatch immediately, and at the 3 second point… STOMP on the accelerator (quickly) 5x and release.
3. When the stopwatch reaches the 15 second point… STOMP-AND-HOLD the throttle pedal to the floor until the Check Engine Light (CEL) starts to blink (around 20 seconds typically).
4) When the CEL stops blinking (in about 5-10 seconds)… release the pedal and immediately START the engine.
5) Let the engine idle for 10 seconds and then rev-up the engine twice.
6) Turn off the engine and wait 20 seconds and you are done.
7) Restart the engine and confirm your idle is remains stable at 650RPM.
End.

If you have a OBD2 test device that will clear your DTC codes you might also consider following these steps to reset your fuel trims:

Instructions
1) Start engine and warm it up to normal operating temperature.
2) Turn ignition switch OFF.
3) Disconnect mass air flow sensor (MAF) harness connector, and restart and run engine for at least 3 seconds at idle speed.
4) Stop engine and reconnect mass air flow sensor harness connector.
5) Make sure Detected Trouble Code (DTC) P0102 is displayed.
6) Erase the DTC memory.
7) Make sure no codes are stored in the ECM.
8) Run engine for at least 10 minutes at idle speed.

I agree OEM (Hitachi) sensors and NGK/NTK usually higher quality products and are used by Infiniti. So today I bought Hitachi # Crankshaft Position Sensor and will install it tomorrow.

Thanks to EdBowy's video on YouTube I also now understand naming these parts is part of figuring out what we are talking about. And in this case the Crankshaft Position Sensor is located underneath the car, on the driver's side, where the transmission mates with the engin block. And is identified by a bright "green" sliding clip that will release the electrical connector. So I have updated the diagram above to show the Cam Shaft Position Sensor is the same part number as the Crankshaft Position Sensor... as identified as #2 & #5 in the picture below.

To be clear, if you have a grean connector to one of these cam or crank sensors, you just "slide-it-forward" to release the connector.

And for more information on how to access this sensor watch these videos:

https://www.youtube.com/watch?v=9uil0Gai7oY

How the bro's do it: https://www.youtube.com/watch?v=VJO1jif_28U

And how the pro's explain it: https://www.youtube.com/watch?v=k3mwZyzWdlQ

TO CONCLUDE: I openned this thread based on the goal of increasing MPG by replacing the Upstream 02 Sensors with the hope that would improve my city-MPG, and my journey has tought me several things:

1) This VK45DE (V8) in my 2004 FX45 is a pig when it comes to city MPG, albiet what's a 8MPG in this Infiniti I enjoy driving vs 12MPG-city I used to get in a V6 Honda. I mean who cares? s*** MPG is just that.

2) I found replacing the upstream O2 sensors was not as easy as I thought so I paid a shop to do it. $400 later, because they upcharged me, my city MPG is still in the toilet at 8MPG in heavy city driving, but my highway MPG is acceptable at 20-22MPG.

Would I recommend you replace your O2 sensors if you are getting 20-22MPG on the highway? ...No!

3) Would I recommend you replace your crank position sensor in you were not experiencing any no-start conditions? ...No!

Conclusions: It's all about weight vs. HP and you can't fight that. The only upside is that I may not end-up stranded on the side of the road anytime soon, because I elected to do some preventive maintenance (PM) by replacing my CKPS tend to fail somewhere between 120K-200K miles. And as for the 02 sensors getting replaced, that was a crap-shoot from the beginning and I lost.

So now my wallet is $600 lighter. or ...You decide?

PS
On my 2004 FX45 the CKPS was on the passenger side where the transmission mates with the engine block and not on the driver's side as implied in the video above. And I decided to us the OEM-Hitachi Part because Japanese cars tend to be finicky about sensors and coil packs. And the O2 sesnsor were NGK.

May thanks to VStar650CL weighing-in. I'm satisfied now.