Login  |  Register
Nissanhelp.com - All About Nissan
Do-It-Yourself Maintenance Owners Manuals Recalls/Campaigns Service Bulletins Service Manuals Nissan OBDII Codes Glossary & Acronyms More...
Member's Ride Photos Stock Photo Gallery
Classifieds - For Sale Classifieds - Wanted To Buy Classifieds - Mechanic Wanted Classifieds - Auto Services Search Auto Parts
Register FAQ Social Groups Mark Forums Read
Fuel trims Forums > > Fuel trims Fuel trims
Forgot Password? Join Us!


Altima Nissan Altima Sedan Discussion Forum

Reply
 
Thread Tools Display Modes
  #1  
Old 09-19-2012, 03:34 AM
naijaboy naijaboy is offline
Enthusiast
2007 Altima
 
Join Date: Dec 2010
Posts: 46
Default Fuel trims

I'm currently struggling with poor fuel economy.
I recently used a code reader and checked my fuel trims and got this

STFT B1- Btwn 14.83- 21.86%
LTFT B1- 13.27%
STFT B2- 24.98%
LTFT B2- 24.98%

O2 B1S1- 0.38-0.42V
B1S2- 0.4-0.8V
B2S1- 0.8V
B2S2- 0.22V

I dont really understand fuel trims so can someone help identify any issues with the above?

Thanks.
Reply With Quote
  #2  
Old 09-19-2012, 11:22 PM
naijaboy naijaboy is offline
Enthusiast
2007 Altima
 
Join Date: Dec 2010
Posts: 46
Default

Anybody???????????????
Reply With Quote
  #3  
Old 09-20-2012, 02:25 AM
bennyb53's Avatar
bennyb53 bennyb53 is offline
Moderator
2019 Sentra
2002 Altima
 
Join Date: Jan 2011
Location: Hawaii
Posts: 2,105
Default

idk how many miles your '07 Altima but if you're near or exceed 100k miles i would replace the O2 sensors.....all four of them as mentioned B1 & B2 so you must have the 3.5 VQ engine. see attached.
Attached Files
File Type: pdf Fuel System.pdf (111.7 KB, 52 views)
Reply With Quote
  #4  
Old 09-20-2012, 02:37 AM
naijaboy naijaboy is offline
Enthusiast
2007 Altima
 
Join Date: Dec 2010
Posts: 46
Default

Thanks.
I've got about 65k miles and the o2 sensors as well as the MAF has been changed.
Ive had an intermittent lean code for bank 2 but it hasnt returned since I changed the o2 sensors.
Ive also had a pending code for P0304 which comes and goes and a slight misfire I can currently feel.
Is there a connection?
Reply With Quote
  #5  
Old 09-21-2012, 01:33 AM
bennyb53's Avatar
bennyb53 bennyb53 is offline
Moderator
2019 Sentra
2002 Altima
 
Join Date: Jan 2011
Location: Hawaii
Posts: 2,105
Default

That is fairly low miles. I assume you replaced the O2 and MAF becasue of trouble codes. My MAF is still OE tho I cleaned it even tho no dtc. I also replace air filter 2x/yr.

Rich condition = more fuel and less air = more oxygen available in exhaust as measured by O2 sensor. Possible causes are leaky or defective injectors.
Lean condition = more air less fuel = less oxygen available caused by intake air leak after the MAF, fuel delivery, vacuum leak, etc. do fuel pressure test.

Misfires are pesky and can be frustrating. Luckily for you its cylinder specific so you know where to start. Inspect your ignition coil be sure mounting bolt is snug and tight, look for cracks in the boot and spring for corrosion, do spark test, inspect spark plug condition, test the circuit, do you experience coolant loss. hope this helps.
Reply With Quote
  #6  
Old 09-21-2012, 01:41 AM
naijaboy naijaboy is offline
Enthusiast
2007 Altima
 
Join Date: Dec 2010
Posts: 46
Default

Thanks again.
Yes I replaced the sensors due to the codes.
The codes still havent come back but the fuel trim seems to indicate the lean condition is still present.
I'll take a thorough look and check for leaks and do fuel pressure test this weekend.
How does a lean condition cause poor fuel economy?
Reply With Quote
  #7  
Old 09-21-2012, 11:26 PM
bennyb53's Avatar
bennyb53 bennyb53 is offline
Moderator
2019 Sentra
2002 Altima
 
Join Date: Jan 2011
Location: Hawaii
Posts: 2,105
Default

Fuel Trim is a program in the drive map that ECM uses to compensate the various driving condition. Example: You turn on the A/C, BCM send signal to ECM requesting higher rpm to compensate the extra load. So ECM send out signal to add fuel by lenghtening the pulse duration say 0.002 milliseconds. It will continue that way as long as the load is peresent. Engineers have pre-programmed the baseline numbers based on driving conditions. When ECM received feedback from O2 sensor, ECM will compare the data and based on that will add fuel or lessen fuel injected. This action is called fuel trim.

I see in the numbers you posted that STFT at 25% and LTFT at 25%. This is unusually high numbers. STFT is short term and when you shut off the engine after your drive all data are erased. But LTFT is long term and the cumulative effect of STFT and stored in the memory. When ECM is adding fuel and reached the upper limit of 25%, it resets. When this condition occurs a few times ECM will ignore the data and will resort to default value which is in rich condition. The same upper limit is true when it is deducting fuel. When engine is operating fairly efficiently you see the STFT during the course of the trip in the range of 5% may be a high of 9%.

When I hook up my scanner with Live Data during a drive I see STFT range of 7.3%, 6.4%, -3.7%, -2.4%, 3.4%, 1.5%, etc. and LTFT sort of mimic the STFT value. But my overall LTFT value is showing 0.7%.
Reply With Quote
  #8  
Old 09-21-2012, 11:34 PM
bennyb53's Avatar
bennyb53 bennyb53 is offline
Moderator
2019 Sentra
2002 Altima
 
Join Date: Jan 2011
Location: Hawaii
Posts: 2,105
Default

i hope you're using Bosch or NGK O2 sensors and after you take care the misfire do the air fuel mixture ratio self-learning found in EC-32.
Reply With Quote
  #9  
Old 09-26-2012, 09:00 AM
naijaboy naijaboy is offline
Enthusiast
2007 Altima
 
Join Date: Dec 2010
Posts: 46
Default

Fixed.

Issue was with the injectors. They were clogged.
Had them taken out and cleaned with thinner.
STFT is now just like yours.
Current LTFT is 0%
Reply With Quote
  #10  
Old 09-26-2012, 06:47 PM
bennyb53's Avatar
bennyb53 bennyb53 is offline
Moderator
2019 Sentra
2002 Altima
 
Join Date: Jan 2011
Location: Hawaii
Posts: 2,105
Default

kudos to you for your effort. very surprising at that mileage. with my 02 Altima i only use Chevron 87 octane probably 99% of the time. that's because Chevron gas already has "techron" additive. you can buy techron at any auto parts store or even wal-mart. if Chevron is available in your area i recommend you use their gas.
Reply With Quote
  #11  
Old 07-06-2017, 03:06 AM
ikiriye ikiriye is offline
Registered User
2007 Maxima
 
Join Date: May 2017
Posts: 10
Default Fuel trims

I am having poor gas mileage of 123 miles per 20 gallons on my maxima 2007
changed air filter, cleaned MAF sensor. car Mileage is 84k and the readings I got at idle are


STFT B1- Btwn -1.6 to -2.3%
LTFT B1- 0.0%
STFT B2- -2.3 to -3.1%
LTFT B2- -5.5%

O2 B1S1- 0.30V
B1S2- 0.47V
B2S1- 0.6V
B2S2- 0.45V
any help will be greatly appreciated
Reply With Quote
  #12  
Old 07-06-2017, 10:26 AM
bennyb53's Avatar
bennyb53 bennyb53 is offline
Moderator
2019 Sentra
2002 Altima
 
Join Date: Jan 2011
Location: Hawaii
Posts: 2,105
Default

123 miles on 20 gal. that's impossible. Fuel must be leaking somewhere. Inspect your fuel line all the way to fuel rail. Is MIL light on?
Reply With Quote
  #13  
Old 07-06-2017, 12:11 PM
ikiriye ikiriye is offline
Registered User
2007 Maxima
 
Join Date: May 2017
Posts: 10
Default

I just don't know where
Reply With Quote
  #14  
Old 07-06-2017, 12:13 PM
ikiriye ikiriye is offline
Registered User
2007 Maxima
 
Join Date: May 2017
Posts: 10
Default

no SES LIGHT
Reply With Quote
  #15  
Old 07-06-2017, 12:16 PM
ikiriye ikiriye is offline
Registered User
2007 Maxima
 
Join Date: May 2017
Posts: 10
Default

With my fuel trim data above does it show something wrong
Reply With Quote
Reply

Tags
fuel, trims

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -8. The time now is 12:39 PM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Search Engine Optimisation provided by DragonByte SEO v2.0.42 (Pro) - vBulletin Mods & Addons Copyright © 2024 DragonByte Technologies Ltd.