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Questions tagged [fuel-trims]

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24 views

Why are my oxygen sensors staying at 1.275v most of the time?

I have an old Volvo s40. Because I had gotten a P0420 code and because of it, an OBD scan tool, I noticed that my fuel trims were very high. Or they could be the result of the age of the car (17 years ...
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0answers
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Jaguar v6 petrol 3.0 2010 STFT and timing all over the place

2010 XF petrol 3.0 P171 and P174 and timing issue For the last few months I’ve had both codes, so the time has come to resolve it, so far no joy, what have I done so far, the car also has a poor idle ...
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0answers
86 views

Need to understand Short term and long term fuel trim numbers

I have the following numbers with idle and at 2000 rpm. What would this conclude? I had a O2 sensor check engine light but even after replacement it had the same engine light after resetting.
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122 views

Analysis of spark plugs [PHOTO] and fuel trims

Again, this is a 2002 Nissan direct injected engine (QR20DD). By judging spark plugs, I assume that the air / fuel mixture is not rich. May be some kind of a lean condition? But the issue is fuel ...
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29 views

AF/O2 and Fuel Trim data - Normal or not?

I'm learning to diagnose my car's poor gas mileage: Car: 2010 Toyota Matrix (Base). Engine: 1.8L, 4 cylinders, Auto, FWD. ODO: 103,000km (64,000 miles). City gas mileage: 12.6L/100km = 18.6 mpg (...
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1answer
265 views

Are mineral oil smoke test machines sensor safe?

So there's heaps of DIY smoke test machines demonstrated around the web. I learned to built one of these, was kinda fun. It worked, even found a crack on my air intake that was messing with the ...
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1answer
78 views

02 honda accord 2.3L, engine shaking and low stft

When the vehicle turns on it will hang around 750 rpm for 1 sec then go to 1250 and stay there. Eventually a p1399 code will come up. I turn the car off then back on and it immediately goes down to ...
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1answer
449 views

Why does my LTFT1 make wilder, faster changes than STFT1?

[1999 4Runner, 6-cylinder 5VZ engine. Not supercharged.] STFT1: Short Term Fuel Trim, bank 1 LTFT1: Long Term Fuel Trim, bank 1 While trying to diagnose a P0171, I decided to observe my fuel trims ...
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543 views

LTFT way too high, O2 seems sane

Issue Car in question is a Renault Clio B 1.2 16V with about 85KKm. I experience two issues: Intermittent starting problems, independent of hot or cold engine. When the problem occurs I need to ...
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1answer
155 views

Can fuel trim (LTFT) be too high or too low? Not using stock injectors

Application is a '97 Jeep Cherokee 4.0L straight-six I installed EV6 fuel injectors to replace the outdated EV1 injectors. The new ones are slightly higher flowing I think. old: 23.2 lb/hr @ 49 psi ...
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2answers
3k views

Help on diagnosing positive Long term fuel trim

My vehicle (Ford Fiesta 2014 Petrol) always have a positive long term fuel trim, which means its running lean mostly. The log data that I recorded using torque pro can be downloaded here : Torque Pro ...
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74 views

2002 Nissan Sentra XE (1.8) bogs down under heavy acceleration

This is my first time asking for help here so please bear with me. As the title says, my 2002 Sentra XE bogs down when my try to accelerate hard. It's more noticeable from a stop, but seems to do ...
2
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1answer
99 views

negative LTFT in bike

I have Bajaj Dominar 400 CC single cylinder bike with FI system.its 7k on odo now.Recently i pluged Diagnostic tool and found my LTFT is negative 11%.My bike has underbelly exhaust with catcon as ...
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932 views

Are (STFT + LTFT) values less than +/- 38% really normal for 2002 Toyota RAV4?

According to a 2002 Toyota RAV4 Repair Manual, "If total of short-term fuel trim value and long-term fuel trim value is within plus or minus 38 percent, the system is functioning normally." Based on ...
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1answer
1k views

High O2 voltage paired with high LTFT reading

What is likely culprit when O2 pegs at .9 volts and stays there indicating engine is rich. Then as this continues for 15 - 30 seconds, the LTFT eventually climbs to +25% or more. Computer calculates ...
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2answers
2k views

P0172 System Too Rich, while fuel consumption is too low

I got this error on my Skoda Fabia 2006 1.2 Bensin 3 cylinder (engine code BME), the car is shaky on idle like it is missing a cylinder, acceleration is non-linear, and fuel consumption is low at 5L/...
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327 views

LTFT high and never changes

Santa Fe 2001 2.7 GLS. LTFT is always +18 on both banks, never changes at any RPM. STFT +4 to +6 Bank 1 and +3 to +5 banks 2 at idle. At higher rpms STFT hangs around Zero but goes up when engine ...
4
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1answer
195 views

What is the the base fuel calculation in a fuel injected vehicle based on?

For a few years, I've been using a Bluetooth <-> OBDII adapter with the Android Torque app. One of the cool things about this is that it's taught me things about a car's operation that I may not ...
8
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1answer
2k views

P0171 and Fuel Trims

I have a 2002 Toyota Corolla (1zz-fe engine) and I am getting a P0171 code - lean condition. I am trying to make sense of my fuel trim values and I was hoping someone could help understand these ...
6
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1answer
1k views

What does the ECU use the long term fuel trim for?

I have a 2001 Honda Prelude SH (Honda H22A4 engine). I was trying to determine how the reported short/long term fuel trims fit in to the fuel control loop (in particular I was wondering if the long ...
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1answer
6k views

Very high short term fuel trim

I was checking my short term fuel trim numbers and o2 sensor switching speed as I think my post-cat sensor has degraded. The car is not throwing a code, and I don't believe that there's a hole in the ...
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3answers
10k views

Cold air intake causing rich condition

This is a follow up question to my initial question which can be found here : LTFT and STFT values are off and don't make sense Car is a 2015 F10 M5 Mods : Cold air intake, aftermarket rear ...
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2answers
1k views

Exhaust Backpressure and Its Impact on LTFT Values

This is a follow-up from my initial question which can be found here : LTFT and STFT values are off and don't make sense. Car : BMW 2015 F10 M5 Modifications : Eisenmann Race Catback Exhaust, ...
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1answer
24k views

LTFT and STFT values are off and don't make sense

Car is a 2015 BMW M5 and it has an aftermarket CAI and a catback (slip on) exhaust. No other performance mods or tunes. About 6-7 months ago, I bought a Kiwi OBD-II reader, simply out of curiosity ...
11
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1answer
3k views

What exactly are fuel trims?

What is meant by the term "fuel trim"? Why are they so important in diagnosing engine operation issues? How do short-term fuel trims differ from long-term fuel trims?