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How to fix high long term fuel trim. 90 (+10%)means ecu is adding fuel.
- How to fix high long term fuel trim. You'll have to make do with the following: When I pull power to the ECU, LTFT starts at 0 and STFT is high positive at idle. Discover common issues, diagnostic steps, and solutions to maintain fuel efficiency and reduce emissions. Dec 4, 2013 · If long-term fuel trim (LTFT) for bank 1 is 25% at idle, but corrects to 4% at 1,500 and 2,500 rpm, focus on factors that cause a lean condition at idle, such as a vacuum leak. Dec 31, 2024 · How a faulty purge valve impacts fuel trim, causing performance issues. The ECM will adjust the fuel trim to compensate for continuous operation in cold or high altitudes. Feb 6, 2010 · Since the OP is experiencing high (20+%) LT fuel trims, that tells me his ECU meters air by MAF sensor and either a) the metered air is correct and there's a fuel delivery issue or b) the fuel pressure/volume is fine but he has unmetered air entering the system. It’s like an alert signaling that something is off with your engine’s air-fuel mixture. Diagnosing and rectifying the underlying cause, ranging from vacuum leaks to faulty sensors, is crucial to preventing performance issues and potential engine damage. So the STFT doesn't have to work as hard. Understanding Short Term and Long Term Fuel Trim (a SD Premium video) I Almost Gave Up - Rough Idling With No Check Engine Light - Mystery Solved! Top 5 Problems Volvo S40 Sedan 2nd Generation Using Short and Long Term Fuel Trims in Diagnostics Hunter Automotive 5. LTFT compensates for longer-term changes such as wear and tear, aging sensors, or modifications to the vehicle. May 19, 2023 · To fix your long-term fuel trim negative issue properly, you need first to diagnose the issue. Have used intake cleaner to check for vacuum leaks. Jan 1, 2020 · The long-term and short-term fuel trims trend nice and smooth between -2 and 8 long term and -8 and 7 short term. Normal range may be high as plus or minus 8, but closer to zero is best. When the o2 sees that air it's going to dump fuel to try and hit the correct ratio of air and fuel. You fix the car and fire it up only to find out the fuel trims are still in the high negative numbers!? Apr 6, 2025 · I would recommend Matt Sanford, GoatRoapGarage, and SilverSurver77 on YouTube. Today I show you how to reset your long term fuel trims, which allows the ECU to relearn the fuel trims. Aug 22, 2023 · A long-term fuel trim stuck at 25% is simply an engine that is running rich. This has also been increasing my long-term fuel trim. On a standard, unmodified engine we would expect these fuel trims to be close to zero. Nov 7, 2023 · It might sound trite, but it’s important to resent your long-term fuel trims once in a while — especially if they stay at 0. It, too, should be close to zero, positive or negative single digits under normal circumstances. (LTFT). If long-term fuel trim (LTFT) for bank 1 is 25% at idle, but corrects to 4% at 1,500 and 2,500 rpm, focus on factors that cause a lean condition at idle, such as a vacuum leak. How Fuel Trim Works Fuel trim adjustments are based on feedback from the oxygen sensors located in the exhaust system. The Airflow tables determine how much fuel to add by dividing the values in that cell for the ideal stoichiometric ratio of your fuel (14. Not crazy high but high enough for me to want to correct the issue. I just changed over from 36 lb injectors to 42. Throttle shaft leaks on a carburetor will cause erratic idle because after setting the idle mixture for smooth idle when the throttle is opened and close the throttle shaft will cause more or less of a leak. Sep 16, 2019 · 2) Long-Term Fuel Trim (LTFT): These adjustments are more gradual and are based on the accumulation of STFT data over time. See full list on cartipsdaily. Depending on if your vehicle has a sensor that reads oxygen, or a sensor that used a wideband, you can use this information to narrow down what could be your culprit. If the corrections exceed a pre-defined limit, the ECM interprets this as a fault in the fuel system and stores a trouble code. The guide is aimed at car enthusiasts who want to maintain their vehicle’s performance and fuel economy. 8L. That's unmeetered air. A few months ago, I had a fuel system cleaning service performed, replaced the distributor, both O2 sensors, cleaned the air filter, replaced the MAP sensor, and installed a new High long term fuel trim 2005 Sentra with 1. 4% like intense told me to do. I am now running into the whole long term fuel trim running too high. If this trend is mirrored in the long-term fuel trim, it suggests an underlying issue like an air intake leak or insufficient fuel pressure. Long term and short term fuel trims are pegged out at -25% and you found the cause of the issue. Aug 20, 2023 · Fix: Both banks showed a high long-term fuel trim (Bank 1 +17% and Bank 2 +23%), indicating a lean condition caused by something that affects both banks. Let the car idle for about 2 minutes with the scanner running, watch the cylinder air mass and the fuel trims (short and long term), add the short and long term fuel trims together to find out what to multiply the correct section of the MAF chart by. The cruising trims are still either adding in +20% or removing a decent amount of fuel at times. I cleaned the MAF sensor with the CRC MAF sensor spray a few days ago with no noticeable improvement. Mar 26, 2025 · Learn about negative fuel trim, its causes, and how it affects engine performance. Short term was floating around 0. 5 lb injectors. We would like to show you a description here but the site won’t allow us. Jun 25, 2022 · If LTFT or total fuel trim is greater than plus 10%, the PCM thinks the air/fuel ratio is too lean and it’s adding fuel to bring STFT control to the correct range. I gave you the long term under various conditions, short term is constantly changing so kind of hard to just give that. The fuel trim is a term used to describe the adjustments made by the engine control module (ECM) to maintain the proper air-fuel ratio. I recommend performing a visual inspection of all vacuum lines, the PCV valve, the brake vacuum booster hose, and the intake gaskets. Dec 6, 2021 · I thought it might be worth noting that the short term fuel trims always compensated to get to <3% total fuel trim but the loss of power and hesitation has been also gradually getting more pronounced. Oxygen sensor fix The oxygen sensor measures the oxygen level in the exhaust gasses. I recently replaced all four oxygen sensors new spark plugs new wires suburban runs very good but fuel mileage isn’t the best 14-16 on the highway at LTFT is measured over time and is usually used to change the air-to-fuel ratio when driving in a steady state. Jun 11, 2025 · Those long-term trends can tell you if something is persistently wrong, which would indicate a much bigger problem. It explains the concept of fuel trim, its importance for engine efficiency, and the steps to diagnose and correct negative long-term fuel trim. What is the normal range of short-term fuel trim, anyway? The STFT B1 normal range of the engine control module is between -22% to +25%. It, too, should be close to zero, positive, or negative single digits under normal circumstances. Aug 19, 2023 · Fix: Both banks showed a high long-term fuel trim (Bank 1 +17% and Bank 2 +23%), indicating a lean condition caused by something that affects both banks. New Custom Tuner Shop hesitates making changes until all potential issues are ruled out. Here’s how you can reset the long term fuel trim: Nov 30, 2023 · This article provides a detailed guide on how to fix negative long-term fuel trim issues in vehicles. A normal long-term fuel trim reading will appear to stay the same, giving a long-term average of fuel added. These sensors measure the amount of May 16, 2025 · Is your fuel trim system lean or out of range? Understand long term fuel trim, post catalyst adjustments, and how to read fuel trim values like a pro. 1. This is the adjustment the engine ECU is having to make to achieve the AFR (Air Fuel Ratio) targets set in the engine map. Aug 21, 2025 · Learn how to read Long Term Fuel Trim (LTFT) for Bank 1, what differ from STFT and LTFT, and explore causes of abnormal LTFT values with real-world case studies. My long term trims are pretty high positive. This helps to make short-term corrections faster and estimate the fuel trim when the oxygen sensors are not up to temperature in open-loop operation. Jul 24, 2024 · The Long Term Fuel Trim Bank 2 High code indicates that there is an excessively rich condition in the air-fuel mixture on the second bank of cylinders in your vehicle. If LTFT goes down with speed, suspect vac leak. Mar 22, 2025 · Once the Short-term fuel trim settles around one number and stops raising, it is a signal for a long-term fuel trim to make a permanent adjustment to the fuel amount. Feb 6, 2017 · 1997 - 2003 F150 - very high long-term fuel trims - I've been having this problem since I've gotten the truck about year ago. 1 I had a good opportunity to show you what fuel trims shouldn't look like so I show that here. Vehicle was at temperature. Positive values indicate the computer is adding fuel (lean condition), while negative values suggest it’s reducing fuel (rich condition). Get a bottle of 'seafoam' in jeep ASAP, Next easier said than done get a fuel pressure check. Ignoring this can lead to poor fuel economy, reduced performance, and even damage to your catalytic Fuel trim is a crucial aspect of internal combustion engine (ICE) functionality that often gets overlooked. This means the engine control unit (ECU) is trying to reduce the amount of fuel being injected because it thinks there's too much. What I learned so far: elevated LTFT happens when 1) MAF sensor under-reports air volume, 2) injectors squirt less fuel, or 3) vacuum leak. The both banks read similar values, so I've concluded the cause is either a dirty/faulty MAF sensor or fuel delivery issue. 200 and 0. Long-term fuel trim is more permanent. These numbers go down as speed increases. Apr 24, 2008 · Short Term Fuel Trim: A STFT value of greater than 1. Thus far I have replaced cam and crank position sensors, MAF sensor, and upstream O2 sensor. An engines long term and short term fuel trims are indicative of how much the engine is needing to compensate to reach a complete combustion. Feb 11, 2022 · Note that if the long-term fuel trim values fluctuate in a pattern that resembles the fluctuations of the short-term fuel trim values suspect a defective catalytic converter. Long-term fuel trim is the record of what the engine controller (ECM/PCM) has been doing over a long period to balance air fuel-ratio. Apr 8, 2012 · We need your short term and long term fuel trims in order to understand what is going on. The vacuum leak is the problem. It determines how the ECU controls the engine's fuel delivery. It even threw 2 codes for both banks being to lean and I explain what could cause that and how to fix Mar 10, 2022 · Idle Fuel trim at those numbers won’t be the cause of bad mileage. P0170 code signals an issue with the fuel trim system on Bank 1 of your engine. Mar 15, 2019 · Note that if the long-term fuel trim values fluctuate in a pattern that resembles the fluctuations of the short-term fuel trim values suspect a defective catalytic converter. 2L e Oct 17, 2024 · As a result, you might notice decreased fuel economy and increased emissions. Click to expand Oct 18, 2024 · The P0171 code indicates that your vehicle's fuel trim system is operating lean. 6 psi. A high Long Term Fuel Trim indicates that an engine is consistently running lean, or the computer perceives it as running lean. Nov 11, 2024 · How to Reset Fuel Trim? Resetting the LTFT can prevent such issues and is accomplished by disconnecting the battery for a few minutes or turning the ignition key to discharge the system. This code typically triggers when the powertrain control module (PCM) detects that the long-term fuel trim value exceeds a predefined limit, usually around 25%. Brucebo » It is extremely important to reset your Long Term Fuel Trim (LTFT) after any work that could possibly affect the engine fuel and ignition system. The fuel trim decreases when I accelerate, but then it rises again. Conversely, a dripping fuel injector results in a rich air-fuel ratio, causing the fuel trim to trend rich (negative Jun 25, 2023 · From some YouTube videos, I’ve educated myself on monitoring short term long-term fuel trims to diagnose intake, leaks, or bad oxygen sensors. I hooked up my scan tool and I see when idle that the long term fuel trim is about 1 % on both banks and the short term fuel trim is about 10%. When you get further into the throttle your long term trims max out at +25%, showing that it's still needing a lot of work to fix the lean condition. Mar 20, 2021 · Long term fuel trims, which can be positive or negative, are “adaptations” calculated by the ECU based on patterns of fuel trim adjustments. May 17, 2019 · I couldn’t find a “fix” posted, but the Xterra’s fuel trim problem is a real-world example of how a fuel trim diagnosis can go awry, so I decided to use its trim numbers and P2A00 diagnostic trouble code (DTC) to illustrate basic fuel trim diagnostics. So if the STFT is -5 for say 10 times in a row it will make the LTFT for that cell -5 and reset the STFT. Start the car and let it run until it reaches its normal operating temperature. Then long-term fuel trim spikes to −35 in about 30 seconds. Thanks, Joe Nov 19, 2017 · Running too rich - High negative fuel trim corrections can be caused by MAF sensor problems, high fuel pressure, leaking fuel pressure regulator diaphragm, faulty evaporative emissions components, leaking injectors, defective O2 sensors, exhaust leaks/pinholes before the O2 sensor, coolant temp sensor problems, and base engine issues such as I can reset the fuel trims to zero, but long-term fuel trim for both banks hits −35 in less than a minute after that. The maf sensor cant compensate for that extra air. If we had STFT +20% before, the LTFT would raise to the same level of 20% and STFT can go back to 0% and stay there unless there is another signal to increase the fuel amount. Apr 2, 2019 · If a fuel trim is high enough to set a code then you either have a vacuum leak, an exhaust leak, an injector problem or an O2 sensor problem. Below are ways you can fix a negative long-term fuel trim. Customer: My fuel trim is elevated, approximately 25%, while my MAP sensor indicates 3. And May 18, 2017 · Long term fuel trim, or LTFT, is the correction the PCM learns over time and stores in keep-alive memory. Fix that vacuum leak and clear the pcm before you start messing with anything else. By troubleshooting and replacing the faulty sensor, you can get your vehicle’s computer back to running smoothly. 0 or a "-" percentange means ecu is removing fuel 1. Jul 21, 2018 · Specifically, long-term fuel trim (LTFT) plays a significant role in diagnosing issues that may arise in the fuel delivery system. multiply the maf curve in that area by 1. 9 (+10%) A STFT value of . This incudes, Aug 16, 2025 · Engine Running Rich? A DIY Guide to Negative Fuel Trim Fixes If your car is running rich, you might be seeing negative fuel trim values on your OBD2 scanner. It does this by collecting information about the air in the engine via the downstream oxygen sensors and balancing it by subtracting or adding fuel. Jan 30, 2018 · 1997 - 2003 Ford F150 - Fixing high long term fuel trim - At idle, bank 1 9%, bank 2 14%. Jan 26, 2021 · How STFT and LTFT/Short Term & Long Term Fuel Trim works. 90 (+10%)means ecu is adding fuel. I just notice the short term FT and drove circled around the parking lot tonight, I found the value was more the 10% when I released the gas paddle, and it dropped to normal around 0% when I hit the gas. If the numbers are +, the engine ECU is having to add more fuel. At least those are the problems that are most common. May 14, 2018 · There are two kinds of fuel trims, short and long term. I changed the injector constant by 16. Feb 18, 2011 · My car's long term fuel trim is 9%. It looks at the trends of the fuel trims. The scan tool displays both the STFT and the LTFT as a percentage. Diagnose causes like vacuum leaks or faulty sensors and follow repair tips to improve fuel economy and performance. What Normal Fuel Trim Values Look Like Fuel Trim values are given as a percentage, indicating the amount of fuel to air in the mixture. Fuel trim refers to how much fuel is added or subtracted by the engine control unit (ECU) to maintain the ideal air-fuel mixture. Significant disruptions in fuel trim ratios may trigger a check engine light, with the May 10, 2025 · Learn what fuel trim system lean and OBD-II code P0171 mean, their symptoms, causes like vacuum leaks or low fuel pressure, and how to diagnose and fix a lean air-fuel ratio issue effectively. When the long term fuel trim on Bank 2 is high, it means that the ECM is making significant Jul 13, 2020 · With the engine idling, look at the Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT) values. Most often, this issue arises from a vacuum leak. 28K subscribers Subscribed Apr 30, 2019 · A negative fuel trim percentage indicates a taking away of fuel while a positive percentage indicates an adding of fuel. Addressing the underlying problem promptly will help prevent further damage and ensure your vehicle's optimal performance and fuel efficiency. All engines, whether gasoline or diesel, require a precise air-to-fuel ratio to operate efficiently. I've run the royal purple fuel injector cleaner through and that allowed me to get the long term fuel trim down, but I can't get the short term to come down. If the numbers are negative, the engine ECU is having to take away fuel. May 27, 2015 · In fact, immediately after starting the engine after resetting the computer, the long term trims went straight back to +15. For example, a vehicle that’s running rich will have negative STFT numbers because the PCM will be trying to correct for the rich mixture by reducing fuel delivery below the factory programming. This incudes, but is not necessarily limited to: Oxygen Sensor MAF Sensor MAP Sensor IAT Sensor Coolant Temp Sensor Throttle TPS Sensor IAC Valve Any Vacuum Line Fuel Pump Fuel Injectors Fuel Pressure Regulator Purge Valve Cannister Apr 2, 2010 · If a fuel trim cell's STFT stays negative or positive for too long then it subtracts or adds to that fuel trim cell's LTFT and resets. 7/1 on gasoline). Mar 31, 2022 · The ECM does not perform a fresh calculation every time it fires an injector. Oct 16, 2011 · Open HPTuners scanner and hit the space bar. How to Fix High Long-Term Fuel Trim A high long-term fuel trim (LTFT) indicates your car's engine control module (ECM) is constantly adding extra fuel to maintain the correct air-fuel ratio. May 13, 2025 · Review Fuel Trim Data: Use a scan tool to monitor short-term and long-term fuel trim values. Sep 9, 2023 · Thanks! Normal Fuel Trim Values are for the sum of both the Short Term and Long Term Fuel Trim values in percentages (Thanks for using percentages and not voltages), and the preferred (or normal range) is typically -10% to +10% So, what does your Short Term Fuel Trim percentages look like? Mar 8, 2022 · P0171 and P0174 coupled with the long term fuel trims are pointing at the fuel pressure/volume. I show how to diagnose for Dec 16, 2012 · Running too rich – High negative fuel trim corrections can be caused by MAF sensor problems, high fuel pressure, leaking fuel pressure regulator diaphragm, faulty evaporative emissions components, leaking injectors, defective O2 sensors, exhaust leaks/pinholes before the O2 sensor, coolant temp sensor problems, and base engine issues such as low compression and incorrect camshaft timing Remember, a high long-term fuel trim is a serious issue that shouldn't be ignored. If I reset the fuel trims and erase the codes, then start the engine cold, fuel trims behave normally until the engine reaches operating temperature at idle. Fuel Trim Data Interpretation Short-Term Fuel Trim (STFT) and Long-Term Fuel Trim (LTFT) values are given in terms of a percentage. One of the main functions of the ECM is to control the air-fuel mixture ratio — which can be short-term fuel trim or long-term fuel trim. So if you are getting 14. Think of long-term as how much weight you gained on average after 40. Always consult your vehicle's repair manual for specific instructions and safety precautions. com Oct 6, 2019 · I've ruled out vacuum leak since LTFTs don't improve at high RPMs. Sep 26, 2022 · Negative long-term fuel trim can be a serious problem, but fortunately, it’s usually easy to fix once you know what’s causing it. This isn't just a minor inconvenience; it can lead to decreased fuel economy, rough idling, misfires, and even damage to your catalytic converter. 00% for a long time. This means the engine isn’t receiving enough fuel in relation to the amount of air entering. Many factors could cause the problem; once you can find the cause, you can fix it quickly. 1 (-10%)stfu means you need to multiply the maf curve in that area by . For example, a disconnected vacuum hose causes the fuel trim to trend lean (positive 10%). The overall engine operation relies on the information from the engine control module (ECM). Any value above or below A normal long term fuel trim reading will appear to stay the same, giving a long term average of fuel added. It is constantly compiling the data to arrive at the long-term fuel trims. Let's dive into the causes and solutions for this common Mar 30, 2022 · The ECM does not perform a fresh calculation every time it fires an injector. The oxygen sensor has gone back to swinging smoothly between 200 and 800 millivolts (0. When this balance is disturbed, it can lead to a variety of issues, some of which can be severe. Short term fuel trims (STFT) represent immediate changes that are happening real time and are erased from the computer’s memory when the engine is shut off. Jun 8, 2009 · It is extremely important to reset your Long Term Fuel Trim (LTFT) after any work that could possibly affect the engine fuel and ignition system. How to Fix a P0170 Code Once you’ve identified the cause, here’s how to address it: Repair Vacuum Leaks: Links Below: Datalogging indicates high Long Term Fuel Trim (LTFT) @ +15%. Does this mean there’s another problem? I should mention that the high pressure fuel pump was replaced back in January. Nov 22, 2024 · Learn how to fix negative long term fuel trim issues in your vehicle. From my understanding, they should be around 10 combined. That was the MAF sensor and vacuum leak. Should probably add your throttle position channel and injector information so you can watch that too. Jan 3, 2024 · Fuel trim is critical when it comes to diagnosing lean and rich conditions. Jan 17, 2025 · Positive Fuel Trim Example: A short-term fuel trim of +15% means the ECM is adding 15% more fuel to address a lean condition. Dec 29, 2016 · When this occurs, the engine control module (ECM) will generate negative long-term fuel trim corrections to compensate. This article explores what long-term fuel trim is, how it functions, and how it can be used to diagnose problems in a car’s engine. It means that too much fuel is going into the engine due to issues with sensors or other important components. I put a fuel pressure gauge on it and it had good pressure when running, but leaked down 15 psi in like a half hour. 800V), and the calculated engine load PID went to 100 percent at the WOT shift point. Sep 21, 2019 · However, when viewing the live data at idle today, I noticed the long term fuel trim to be -13. Aug 19, 2023 · Once the Short-term fuel trim settles around one number and stops raising, it is a signal for a long-term fuel trim to make a permanent adjustment to the fuel amount. Learn more about STFT and LTFT/Short Term & Long Term Fuel Trim. Does anyone on here know how to lower this via hp tuners? I'm still new to the whole hp tuner thing so please be as specific as you can. 4 days ago · Learn about long-term and short-term fuel trims, their importance, and how to interpret them for optimal vehicle performance in this blog post. Jun 1, 2024 · STFTs stand for “Short Term Fuel Trim”. Sep 27, 2023 · Learn what the P0171 code means, the common causes of a lean fuel trim in bank 1, and how to fix it with our expert guide. 6 instantly even though the short term trims stayed right around 0. it has very high long-term fuel trims and it seems no matter what I do I cannot get them to go down my fuel trims at idle are 39 Bank1 and 33 bank2 they go down to around 12>7 while driving. Learn how it impacts engine and what steps you can take to fix it. Always verify the STFT (short-term fuel trim) and the LTFT (long-term fuel trim) while reading live data from your Innova OBDII scan tool. Aug 3, 2025 · High long-term fuel trim (LTFT) readings indicate that your engine’s computer is consistently adding fuel to compensate for a lean condition. 7g of air, then you need 1g of fuel. Did some data logging and notes that my LTFT is high. In this video I am going to explain how your short and long term fuel trims are calculated, than we'll try to diagnose a problem on a 2003 F150 with a 4. j9syk oy ujn puqr zzf2 rd6cv8 vv08u 4tbw 7hs tes