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Discussion Starter · #1 · (Edited)
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?

Here's a chart I created with extra information and part numbers I have be compiling for your library.


Motor vehicle Font Parallel Diagram Auto part
 

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Discussion Starter · #2 ·
In another Infiniti Forum, one professional mechanic comments he has only seen "bad results" from using Bosch O2 sensors and recommends Denso or to use the same OEM type that came with your car.

So I did 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. You can also print out the attached pdf file.

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/B07YHDFSP3/ref=ppx_yo_dt_b_search_asin_title?ie=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.
2003-2012 Infiniti FX35 - FX45 Accelerator Pedal Released Position Learning Procedure | Infinitihelp.com

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)
2003-2012 Infiniti FX35 - FX45 Throttle Valve Closed Position Learning Procedure | Infinitihelp.com
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.

2003-2012 Infiniti FX35 - FX45 2003-2012 Infiniti FX35 - FX45 Idle Air Volume Learning Procedure | Infinitihelp.com

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.
Here’s a chart to describe the above steps in strict secquence.

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)

2003-2012 Infiniti FX Clear Mixture Ratio Self-Learning Control Data | Infinitihelp.com

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.
 

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Discussion Starter · #3 ·
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.


Conclusions: From these numbers at idle I believe my ole O2 Sensors are still operating normal. So I will not be replacing them. And if I can confirm my city MPG is better, by virtue of reading the onboard MPG computer, I will let you know.
 

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Discussion Starter · #4 ·
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?
 

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Discussion Starter · #6 · (Edited)
Ever figure it out?
Yes & No. I was hoping other FX45 owners would reply with their MPG measurements for comaparison before I thru more money at this problem. ...But no one did.

In the meantime, I researched this subject even futher and came to these conclusions:

1) A number of Infiniti oweres were having problems with the Bosch brand of O2 sensors, but this may or may not apply to the 8-cylinder FX45, because all my findings came from V6 owners.

2) Apparently, the NGK brand of 02 sensors were the best sensors to buy. The problem is that the NGK type ran ~$100 each, and since there were 2 of them ($200 total) I decided to pass on this fishing expedition due to cost.

You now what they say: "If it aint broke, don't fix it!"

However, I suppose you can buy some cheaper Bosch 02 Sensors on Ebay and see if your MPG improves. Let us know if you go this route. I decide not to bother, but had I been able to get some NGK O2 Sensors at a good price, I may still give it a try, if for nothing else to confrim that a number of people say: Just becasue your O2 Sensor is not tripping a CEL, that does not mean the sensor is good. And I this case, a marginal "Upstreem" O2 sensor may produce poor city MPG, but will also product good highway MPG. (Which is my complaint.) So, while I think it's possible my Upstream O2 sensor is marginal, I was not willing to spend the money to find out, but I think there is a 20% chance this is a contributing factor.

Replacing the 02 sensor is easy, but I recommend you spray some thead bustor on the bung and let it work its magic for a day before you unscrew your sensor.

Also, some people say you should use the same brand of 02 sensor that came from the factory, and I think this too is a good idea.

Other MPG killer include your MAF Sensor, and IMO you should only but the OEM type or the aftermarket types sold at Napa, because the cheap MAF Sensors on Ebay will 50% of the time cause you problems, just like buying cheap coil packs on Ebay. DON'T DO IT. A number of people end up with blow ECM boards from cheap coil packs; and have reported engine misses and very expensive mechanic bill from trying to diagnose problems 100-200 miles afer they installed these cheap China knockoff parts.
 

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I get about 15 city and today on hwy going 60mph I was averaging 22.5
My problem is I randomly lose power. It doesn't run rough it will just not want to accelerate so effortlessly like normal. I view live data and don't see anything off but it only does it every so often.
I also used my computer to do the 2* timing mod so my mpg was about 16.5 city previously.
 

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Discussion Starter · #8 · (Edited)
I would think it's possible that if you randomly lose power, you might do some YouTube searching on that subject... to see if the Crank Position sensor is a contributing factor. And don't forget about the MAF Sensor as a possible cause too.

If it was my car, I would clean the MAF using only MAF cleaner. (This is very easy and cheap to do.) ...But watch a YouTube video on the subject for some additional tips.

This video on MAF talks about performance/hesitation when accelerating on to a freeway:

===
Can you be more specific and tell us what you feel, or what the car does, when you lose power? ...And how often it occurs and when it occurs if there is a pattern?

How many miles on your car and what year is it?

Here's a good reference on both the CPS and the Cam Positiion Sensor: M45 2006 Camshaft Sensor P0340 - Nissan Forum | Nissan Forums
 

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I have new factory crank and cam sensors straight from the dealership.

I clean the maf with maf cleaner frequently as well as cleaning out the throttle body and doing the throttle body reset and fuel trim reset.

It just doesn't accelerate like normal. Feels like timing is reduced. It'll happen a couple times a week randomly while driving. After driving the car later it'll be normal.
Doesn't correlate with the 02 sensors going into open loop.

Could be
-maf
  • throttle body
  • 02 sensors
  • knock sensors
-something to do with the vacuum/solenoids associated with the variable runners
- wiring harness associated with said sensors
-possibly an oil issue since I believe it needs proper oil for advanced timing with associated sensors

I get 0 codes and live data looks fine
2004 165k
 

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I'm impressed and appreciate the time you put into these informative posts. I wish I could contribute data but I stopped paying attention to MPG on my FX45 [2 other daily drivers] and focus on just enjoying it.

I don't know if there is a test for the condition of your catalytic converters. Our 45 suffered a massive internal failure on the hightway- no warning at all [passed emissions tests, no warning lights, no rattles, etc]. The fix ended up being replacement of all the cats and 02 sensors [California only specification $$$$ AND the only thing our Air Resources board will accept is OEM CA spec]. I spent more than the vehicle is worth. While I was at it installed new spark plugs, etc. Slight improvement in economy and notable improvement in performance. I can't say I'd recommend such an extreme fix to anyone else but I do enjoy the improved performance. FWIW.
 

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Discussion Starter · #14 ·
UPDATE: I found several things that you all my like to know:


1) I found cleaning the MAF with MAF cleaner did NOT do as good a job restoring that "pep" and very quick throttle response we all had to get used after we first bought our FX45. So, it appears to me, that if you find your throttle response becoming more typical of a "beefy V8" then you might consider buying a new MAF sensor on Amazon for $25 instead of cleaning your old one.

2) And if you have over 100,000 miles, then I would also recommend you change your OEM NGK spark plugs (LFR5A-11) with the Denso Iridium SK16HR11 spark plugs (same heat range). Note: The back spark plugs are the only hard ones to get to, but with 2-short-3/8" extensions and a 5/8" socket you and manage pretty easily. This only scary thing about this job is the first time your remove the throttle body "snorkel tube" which easily flips out of the way after you remove the MAF Tube and loosen the hose clamps. Then you see your valve cover underneath with the spark plug tubes underneath. (Only a 1.2 hour job for the experienced; and 2 hours for us first-timers.)

3) My OEM PCV valve mostly failed the "rattle test" so I replaced it... But only hand tighten so you con't crack the plastic valve cover.

4) This is a good time to check and/or tighten your valve cover bolts ~1/8" turn.
Note: My valve covers started to leak in the back on the driver's side and in the front on the passenger side, but after putting 1/8" turn on the valve cover bolts (following the zig-zag torque sequence from the center of the valve covers to the outer ends) I was able to stop the oil leak... and for good measure I used added a small bottle of "Blue Devil" Stop Oil leak to my engine oil.

Parts:
Spark Plug extension: https://www.amazon.com/dp/B01BVSA3S8?psc=1&ref=ppx_yo2ov_dt_b_product_details
PCV Valve: https://www.amazon.com/dp/B001UEDHC8?psc=1&ref=ppx_yo2ov_dt_b_product_details
MAF Sensor w/Tube: Amazon.com: 22680AR200 22680AR20A SCITOO MAF Mass Air Flow Sensor FITS FOR 2004 for Infiniti FX45 4.5L,2003-2004 for Infiniti M45 4.5L,2002-2004 for Infiniti Q45 4.5L : Automotive
Blue Devil Stop Oil Leak: https://www.amazon.com/BlueDevil-Pr...p+oil+leak&qid=1663640462&s=automotive&sr=1-2
 

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Discussion Starter · #15 ·
I also want to provide BETTER throttle relean steps that are easier to follow. This is needed if you find your idle RPM does not equal 650RPM.


After cleaning the throttle body my engine idled high (750RPM) and my CEL was on. I then found a P0507 code on my code reader.
The fix was to follow these throttle relearn steps exactly as written below:

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
=== The following steps should reset the idle to 650RPM with all loads off. ===
1. Drive the car sufficiently to reach normal operating temperatures.
2. Parked, with front wheels straight ahead, and every DC load off, I.e. Radio, lights, wipers, heater, etc. follow these steps:

3. Turned the key-off, waited 10 secs.
4. Turned the key-on, start a stopwatch immediately, and at the 3 second point… STOMP on the accelerator (quickly) 5x and release.
5. 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).
6) When the CEL stops blinking (in about 5-10 seconds)… release the pedal and immediately START the engine.
7) Let the engine idle for 10 seconds and then rev-up the engine twice.
8) Turn off the engine and wait 20 seconds and you are done.
9) Restart the engine and confirm your idle is remains stable at 650RPM.
 

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Discussion Starter · #16 ·
I came up with an easier to follow when it comes to these Throttle Relearn Steps:

After cleaning the throttle body my engine idled high (750RPM) and my CEL was on. I then found a P0507 code on my code reader.
The fix was to follow these throttle relearn steps exactly as written below:

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
=== The following steps should reset the idle to 650RPM with all loads off. ===
1. Drive the car sufficiently to reach normal operating temperatures.
2. Parked, with front wheels straight ahead, and every DC load off, I.e. Radio, lights, wipers, heater, etc. follow these steps:

3. Turned the key-off, waited 10 secs.
4. Turned the key-on, start a stopwatch immediately, and at the 3 second point… STOMP on the accelerator (quickly) 5x and release.
5. 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).
6) When the CEL stops blinking (in about 5-10 seconds)… release the pedal and immediately START the engine.
7) Let the engine idle for 10 seconds and then rev-up the engine twice.
8) Turn off the engine and wait 20 seconds and you are done.
9) Restart the engine and confirm your idle is remains stable at 650RPM.
 

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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?

Here's a chart I created with extra information and part numbers I have be compiling for your library.


View attachment 20655
When comes to sensors you're better off getting OEM. 🤙
 

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Discussion Starter · #18 ·
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 on the NICO Forum. I'm satisfied now.
 
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