The longterm fuel trim ltft is a stored value which accounts for changes in engine condition, wear and tear, etc. To accomplish this the ecu increases or decreases fuel delivery by increasing or decreasing the time that the injectors are open. It consists of the base fuel map bfm which is hard coded into the ecm, and the adaptive ltft. Engine performance diagnostics by scannerdanner scanner danner. For more information on this topic, i have written a field manual called. Nexzor reserves the right to change or improve its products and to make changes in the content without obligation to notify any person or organization of such changes, additions or improvements. Keep in mind that both leaking fuel injectors and vacuum leaks will have less effect at higher rpms. Fuel trims indicate how much fuel the computer is adding to the engine from the signals it receives from the o2 sensors. One, to consistently control the engine fueling to maintain a stoichiometric or 14. Once the longterm trim is in place, the shortterm continues to operate and go positive or negative as needed past the standing longterm trim.
Technician b says you can toggle between function codes 04 and 08 by. Engine performance diagnostics by scannerdanner scanner danner scanner danner, paul danner, paul danner on. Adaptive fuel dtcs diagnostic techniques p0171p0174 ford. The purpose of the ltft is to get the airfuel ratio back to stoichiometric in the event of a faultnormal wear so the stft can again cycle between rich and lean operating conditions.
Note that the injector size will automatically reduce the overall fuel and cranking fuel even if the trims are set to zero. I created a no fuel misfire and an ignition misfire on both systems. Here is an explanation of fuel trim and what it does for us. Use these videos to support sections 4 and 5 fuel trim and o2 sensor. The term additive is used because of the way fuel is added to the mixture. How to quickly identify a vacuum leak using fuel trim and water. Using fuel trim as a diagnostic tool can to improve vehicle engine power and economy is the focus of this avi video lbt177 fuel trim diagnostics with jim wilson. Engine performance diagnostics by scannerdanner scanner. Trim codes or trim files are codes that go into an electronic control module ecm that determine how long a fuel injector injects fuel into a cylinder for. The two parts of a computer fuel trim adaptive strategy are short term fuel trim stft additive and. Fuel trim diagnostics using fuel trims during a diagnostic plays an important function in plotting a trend, be it either a rich or lean trend. Acknowledgements general motors, the iagmasep association board of directors, and raytheon professional services, gms training partner for gms service technical college wish to. Fuel trim is a twopart adaptive strategy that adjusts fuel injector pulse width open time to adapt to wear, defects, or changes in the system.
Aug 16, 2019 trim codes or trim files are codes that go into an electronic control module ecm that determine how long a fuel injector injects fuel into a cylinder for. Negative fuel trims at idle ericthecarguy stay dirty. Technician b says you can toggle between function codes 04 and 08 by pressing buttons 4 and 8. May 08, 2006 understanding fuel trim some of the most common fault codes dtcs pertain to fuel trim rich mixture, lean mixture, etc.
Trim codes only apply to electronic caterpillar injectors and some newer electronic cummins injectors. How to diagnose a misfire a scannerdanner premium training. How to quickly identify a vacuum leak using fuel trim and water0rqn9ybmzig. Bmw and mini longterm and shortterm fuel trim diagnosis. Using fuel trim to help diagnose vehicles takes practice, but you also need to understand how each component affects fuel trim when in operation. Stft reads opposite of ltft after repair fuel trim data youtube. On scannerdanner premium i will bring you right into my classroom at. Gen iii speed density ve table and maf tuning instructions with a wideband o2 sensor create by 69lt1bird jeff anderson 2 system is operating rich, long term fuel trim will compensate for the rich condition by decreasing. Short term fuel trim is what the computer is doing at that time to control the fuel mixture. The two parts of a computer fuel trim adaptive strategy are short term fuel trim stft additive and long term fuel trim ltft multiplicative. Gen iii speed density ve table and maf tuning instructions.
To diagnose, i connected a blue driver scanner and checked live data compared to what the trucks service manual specifies. Using fuel trim to identify type of misfire can it be done. For more information on this topic, i have written a field manual called engine performance diagnostics which is available as an ebook or paper book. Understanding short term and long term fuel trim a sd. The purpose of any fault diagnosis is the elimination of known good components. In addition, i also offer a library of video resources, showing how to perform the diagnostic techniques taught both in my book and in my class.
I even fixed my furnace at home using these same principles. After showing you guys and my class the operation of an oxygen sensor on a motorcycle, i used this opportunity to discuss a very difficult topic from chapter 5 in. Use these videos to support section 1 universal testing methods of my engine performance diagnostics field manual available at. Then i will show you how to use fuel trim numbers to determine whether or not. Fuel trim and oxygen sensor testing scannerdanner premium. Scannerdanner llc assumes no liability for property damage or injury incurred as a result. Understanding fuel trim some of the most common fault codes dtcs pertain to fuel trim rich mixture, lean mixture, etc. Fuel trim is the fine tune control of fuel delivery by the ecu. The fuel trim ratios represent the amount of fuel the pcm is adding or removing in reference to a baseline to keep the mixture at optimum based on feedback from the o2 sensors, temperature sensors, etc. How to diagnose a misfire a scannerdanner premium training video. Fuel trim diagnosis maintenancerepairs car talk community. If you are trying to diagnose drivability issues but dont have any trouble codes to chase, take a closer look at the vehicles fuel trim. Using fuel trim to identify type of misfire can it be. Adaptive fuel dtcs diagnostic techniques p0171p0174.
Obdii primer using fuel trims for diagnostics in the first paper we saw what fuel trims are and how they work, now well put them to use and see what they tell us about whats going on in our engine. Chapter 4 oxygen sensors and fuel trim an sd premium. Using fuel trim as a diagnostic tool motor age training. Additionally, links to over 50 scannerdanner videos are included which explore the content of the book in more detail. The maf sensor was listed as a possible cause, but in order to make an efficient repair, its important to understand how fuel trim data can help point you in the proper direction. The ecu controls airfuel mixture in order to maintain power, efficiency, and emissions. Understanding short term and long term fuel trim a sd premium. Note that vacuum leaks after the throttle body cause negative fuel trims at idle on speed density systems. The ecu will now run selftests on the misfire detection, fuel trim, and evap purge flow. Learn more about scannerdanner s favorite products. He inverts the signal, adjusts time and trigger levels, changes the horizontal position of the signal, and takes cursor measurements. Gen iii speed density ve table and maf tuning instructions with a wideband o2 sensor create by 69lt1bird jeff anderson 2 system is operating rich, long term fuel trim will compensate for the rich condition by decreasing the injector pulse width, and a negative long term fuel trim is indicated.
This is a scannerdanner premium video recorded during my class at rosedale. Included in wilsons discussion to achieve this goal, which can lead to selling more fuel injection work, is the part fuel sensors and catalytic converters play in fuel trim. Using fuel trim to identify type of misfire scannerdanner premium. The purpose of the ltft is to get the air fuel ratio back to stoichiometric in the event of a faultnormal wear so the stft can again cycle between rich and lean operating conditions. Both my free channel scannerdanner on youtube, and my paid subscription channel scannerdanner premium have coordinated playlists that match the chapters in my book and the flow of my class. Chapters 4 and 5 fuel trim and oxygen sensor testing chapter 6 temperature sensor, thermistor circuit tests chapter 7 potentiometerposition sensor tests tps, evp, app, vaf etc chapter 8 pressure sensor testing, map, baro, dpfe, fuel tank and rail pressure sensors chapters 9, 10 and 11 the 5v reference and signal circuit quick tests. He inverts the signal, adjusts time and trigger levels, changes the horizontal. Content current flow voltage signal air fuel mixture low o. Positive fuel trim means the computer is adding extra fuel too lean. Short term fuel trim this is an immediate correction. Chapter 1 misfire id, compression tests, vacuum leaks, fuel trim, head gasket, restricted exhaust. The longft12 pids will display the fuel trim currently being used at that rpm and load point.
Being able to interpret your scanner fuel trim data requires a basic knowledge of the interaction of short term fuel trim and long term fuel trim data. Fuel leaks vacuum hoses disconnected or split see figure 314 corroded connectors unusual noises, smoke, or smell check the air cleaner and air duct for restrictions. Fuel trim download can be obtained atfuel trim download can be obtained at atechtraining com. Adaptive fuel dtcs diagnostic techniques p0171p0174 adaptive fuel dtcs diagnostic techniques before proceeding, attempt to verify if any driveability concerns are present. Information in this document is subject to change without notice. Gm fuel composition reset snapon diagnostics product forums. Open loop fuel system statusopen loop fuel system status due to fault status with all the. Scannerdanner uses the uscope with a low amp probe on a 99 honda civic with no spark. During this time the oxygen sensor o2 response, air intrusive ais system, egr flow, purge valve, misfire detection, and fuel trim diagnostics will be performed. Chapters 4 and 5 fuel trim and oxygen sensor testing youtube.
Conversely, if additive fuel trim is outofspec in the positive direction and the multiplicative trim is within spec, chances are the car has an intake vacuum leak rather than a failing maf. The engine control module ecm controls the airfuel metering system in order to provide the best possible combination of driveability, fuel economy, and. Our universal, directfit, carb, high performance and diesel converter lines cover over 100,000 applications, including obdii coverage for all 50 states and are certified in 58 countries around the world. Fuel trim numbers fuel trim download can be obtained atfuel trim download can be obtained at atechtraining com. Use the information to target the next diagnostic steps. This first article ive started at page 3, just so youre aware. Technician a says you can switch sequentially through display groups by pressing the r or c button.
Scan tool basics this will help you prepare for the nc3 snap. The ecu controls air fuel mixture in order to maintain power, efficiency, and emissions. The rest of this series on oxygen sensors and fuel trim can be. On scannerdanner premium i will bring you right into my classroom at rosedale. The cranking fuel trim is applied when starting the engine. What i have read mentions that this would show that the truck is running rich and the fuel trim is trying to compensate, but only at idle. Ive used this to cure fuel trim problems caused by adding too little fuel to trip a reset or relearn. How to use fuel trim to identify the cause of a p0171 and p0174 code. In general, if a shortterm trim goes above 10%, this creates a longterm fuel trim that is semipermanent the exact way that this happens, as well as threshold percentages, varies by manufacturer. I am not teaching widebandnarrow band o2 operation here, just fuel trim reaction to a misfire. Eastern catalytic manufactures catalytic converters, manifold converters and converter components for aftermarket and oems. Note that clearing fault codes even if no fault codes exist will also reset the fuel trim values to 0, so it is essential to. Engine performance diagnostics by scannerdanner scanner danner pdf for free, preface.
The hanatech scanner will display voltage data as shown in the table below. Now hold your vehicle speed steady at 55mph for three minutes. The overall fuel trim is an additional compensation applied evenly to the main fuel tables. Additive fuel trim has the most influence at idle range loads, but is also used off idle for minor trimming adjustments. Observing these changes in longft12 can help when diagnosing fuel. Using fuel trim to help diagnose vehicles takes practice, but you also need to understand how each component affects fuel trim when in. The fuel map is a two dimensional table of values, sort of like an excel spreadsheet, for how much fuel to squirt, based on engine rpm and load value. Ive used this function in the past on other gm vehicles that dont have the sensor but use an algorithm based on fuel level changes to adjust composition settings. Learn what does p0175 chevrolet fuel trim system rich bank 2 means, location and how to repair. Find the prices for normal auto service activities including alignment, tuneup, timing belt replacement and more. Fuel trim question poor mileage scannerdanner forum. The attached screenshot shows that bank 1 and bank 2 long term fuel trim are showing 24.
Im wondering why the reset did not work on the 20 impala. Chapters 4 and 5 fuel trim and oxygen sensor testing. Monitor and record the fuel trim values in the four common operating rangesidle speed, light load 20 to 30 mph, moderate load 40 to 50 mph and heavy load 60 to 70 mph. For more information on this topic, i have written a field manual called engine. Engine performance diagnostics by scannerdanner scanner danner pdf.
Youtube free menu chapter 1 misfire id, compression test, vacuum leaks, fuel trim, head gasket, restricted exhaust, low power, dvom. This book is the printed version of scannerdanners ebook. Engine performance diagnostics fuel injection vehicle parts. Eastern catalytic converters apc automotive technologies. With the free videos i am providing here, combined with my book and online classes on.