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  #1  
Old 09-19-2012, 04:34 AM
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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.
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  #2  
Old 09-20-2012, 12:22 AM
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Anybody???????????????
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  #3  
Old 09-20-2012, 03:25 AM
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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, 27 views)
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  #4  
Old 09-20-2012, 03:37 AM
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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?
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  #5  
Old 09-21-2012, 02:33 AM
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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.
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  #6  
Old 09-21-2012, 02:41 AM
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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?
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  #7  
Old 09-22-2012, 12:26 AM
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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%.
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  #8  
Old 09-22-2012, 12:34 AM
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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.
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  #9  
Old 09-26-2012, 10:00 AM
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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%
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  #10  
Old 09-26-2012, 07:47 PM
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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.
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  #11  
Old 07-06-2017, 04:06 AM
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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
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  #12  
Old 07-06-2017, 11:26 AM
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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?
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  #13  
Old 07-06-2017, 01:11 PM
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I just don't know where
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  #14  
Old 07-06-2017, 01:13 PM
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no SES LIGHT
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  #15  
Old 07-06-2017, 01:16 PM
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With my fuel trim data above does it show something wrong
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