Jan 19, 2012 38 videos play all chapters 17, 18 and 19 fuel injector testing scannerdanner understanding short term and long term fuel trim a sd premium video duration. After injecting the fuel for that cycle the ecu reads the o2 sensor and sees if the engine is rich or lean. Fixed fuel trims analyzing pending lean codes was created by charles acosta at the 850 mark i start to go wot. Fuel trim question poor mileage scannerdanner forum. If the ecm sees it has to keep adding fuel for a period of time, it basically assumes that is the new normal and increments the long term trim by that amount. Cranking fuel trim applied when starting the engine. Fuel trim spread is greater than 10 points, bank 2. This book is the printed version of scannerdanners ebook. To better understand how fuel trim is used to maintain the proper airfuel ratio, look at the set of fuel injectors in fig. Using fuel trims during a diagnostic plays an important function in plotting a trend, be it either a rich or lean trend. The pcm starts out with a baseline fuelair mixture that it believes will achieve a stoichiometric ratio. The o2 sensors will be the indicator or as one of my students has said, is. Scanning obdii fuel trims explains the fuel control pid obd2 scanner parameter.
How to use fuel trim to identify the cause of a p0171 and p0174. Now with gdi engines there is very little fuel injector pulse. How to interpret fuel injector waveforms a scannerdanner. Understanding short term and long term fuel trim an sd. You have a ol fault so its stuck in open loop forever with no fuel trim corrections until. Diagnostic trouble code dtc p0171 fuel trim system too. Fuel trim is broken down to two types, short term and long term. Using fuel trims and downstream o2s to analyze intermittent misfire. Jun 12, 2015 avi can help with fuel trim diagnostics. The longterm fuel trim ltft is a stored value which accounts for changes in engine condition, wear and tear, etc. Understanding short term and long term fuel trim a sd premium. Sorry man, just read more and what youre describing is bad upstream o2s sensor. There will be a deflection in the adaptive terms which is capable of identifying a slow default emerging in case the adaptive value threshold is permanently exceeded.
A dirty fuel filter and bad fuel pressure will increase trims as well. Fuel trim spread is greater than 10 points, bank 2 tacoma world. As for finding the split fuel pressure regulator hose on the car you are working on, this may have been one reason the fuel trims were so negative, however, not all cars actually have vacuum controlled fpr, some may have hoses attached to the fpr, but they often just lead to filtered air inside the air filter box, the fpr holds a static fuel. I began teaching this technique to ford technicians in the. Clogged fuel injectors inefficient spray symptoms will be above normal injector pulse width at idle normal values are around 3. My short term is climbing 20% on both banks which tells me its a rich command for a lean condition and its happening at the moment of wot not long term memory. The disc will go into a computer and the computer will get connected to the ecm. Gm 3800 service tips, techniques, and advice facebook. Here is an explanation of fuel trim and what it does for us. Overall fuel trim an additional compensation applied evenly to the main fuel tables. This change in fuel being added or taken away is called fuel trim.
This book is the printed version of scannerdanner s ebook. Stft reacts directly with 02 sensor input 900 200mv with an average of 450mv, the short term fuel trim is a direct reaction to the 02 sensors. Bank 1, sensor 1 upstream sensor is used to analyse afr and adjust fuel trim and mixture accordingly. It uses your scan tool to watch the fuel trims and the downstream o2 sensors. My fuel saver works well for the first trip of about 10 miles after engine warm up.
After that, the mpg reduces for subsequent trips on the same day. Injector pulse width changed by allowing fuel trim short term or long term to add or subtract to the fuel injection pulse width. Use these videos to support section 1 universal testing methods of my engine performance diagnostics field manual available at. Changes in o2 sensor voltages cause a direct change in fuel. The calc button enables the overall fuel trim to be calculated from changes in fuel pressure or engine displacement. Technician a says the rich fuel mixture has clogged the catalytic converter and a back pressure test should be performed. Technician b says a vacuum gauge can be used to diagnose a. Diagnostic trouble code dtc p0171 fuel trim system too lean. The pcm needs this information for adaptive strategy known as short term fuel trim and long term fuel strategy. For more on understanding and using fuel trim go to. Note that the cranking fuel is automatically compensated for the injector. Comparison of fuel trim data for v type engines when the system utilises fuel system monitoring is a good way to see if a problem exists on one bank or is affecting both banks.
Nov 11, 2011 fuel trim is the amount of fuel added or subtracted by the pcm. Additionally, links to over 50 scannerdanner videos are included which explore the content of the book in more detail. 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. Since the standardization of obdii, fuel trim is found on most cars.
Chapters 4 and 5 fuel trim and oxygen sensor testing. Troubleshooting p0171, p0174 trouble codes how to read. After repairs, use the scan tool fuel trim reset function to reset the longterm fuel trim to 128 0%. The mpg for the the first trip after overnight storage is the best. Fuel trim is the internal mechanism within the pcm that switches the fuel mixture from rich to lean. Scannerdanner premium is a paid subscription channel which offers you the opportunity to be part of my engine performance class at rosedale technical college. The st being negative at the same as the lt trim being positive just means that this load cell has not adjusted to the new mixture condition. Find the prices for normal auto service activities including alignment, tuneup, timing belt replacement and more. Stft and ltft values will be displayed by number e. Short term fuel trim is what adjusts and changes the long term fuel trim numbers. The ecu reads a base fuel table and multiplies this look up table 3d matrix table by the long term fuel trim. The overall fuel trim is an additional compensation applied evenly to the main fuel tables. When the feedback from the ho2 sensors shows a deviation, the pcm adjusts the amount of fuel the injectors deliver, in an effort to hit the stoichiometric goal. Understanding fuel trim some of the most common fault codes dtcs pertain to fuel trim rich mixture, lean mixture, etc.
The ltft is also influence by the short term fuel trim stft. 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. The truck was recently tuned up with new plugs, wires, cap, rotor, and coil. I also tuned mine by feel, but i doubt its right and i should have it done. Use these videos to support sections 4 and 5 fuel trim and o2 sensor testing of my engine performance diagnostics field manual available at. When we talk about fuel, trim we have to keep in mind that the o2 sensor is the heart of the fuel control system. Long term trim ratios vary less thus they are long term. Jan 16, 2010 a fuel trim which is highly positive may indicate the ecms attempt to correct a lean conditions, and a higly negative trim is an attempt to correct for a rich condition. How to use fuel trim to identify the cause of a p0171 and p0174 code. Long term fuel trim is what the computer has learned over a certain duration of time to control the fuel mixture. Once that happens, the short term trim is again bouncing around 0%.
The vehicle is now backfiring and has a lack of power. 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. The ecu controls air fuel mixture in order to maintain power, efficiency, and emissions. My short term is climbing 20% on both banks which tells me its a rich command for a lean condition and its happening at. 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. May 15, 2008 importance of reseting fuel trim ltft. Being able to interpret your scanner fuel trim data requires a basic knowledge of the interaction of short. Mogelijke oorzaken van een te rijk mengsel negatieve fuel trim. Fuel trim is the amount of fuel added or subtracted by the pcm. The cranking fuel trim is applied when starting the engine. The close loop system is designed to rapidly change the airfuel ratio from slightly rich to slightly lean to maintain a. Monitoring fuel pressure while driving the vehicle at various road speeds andor loads may become necessary here.
He explains how things like high mileage, dirty injectors, lazy o2 sensors or coking affect shortterm fuel trim. May 08, 2006 understanding fuel trim some of the most common fault codes dtcs pertain to fuel trim rich mixture, lean mixture, etc. If i understand the o2 monitoring system on these trucks correctly those who know something i dont please chime in. Fuel pressure an excessively low pressure will make the system lean. A fuel trim which is highly positive may indicate the ecms attempt to correct a lean conditions, and a higly negative trim is an attempt to correct for a rich condition. A fault code indicating a rich air fuel ratio has been repaired by replacing a leaking fuel injector. Chapter 1 misfire id, compression test, vacuum leaks, fuel trim, head gasket, restricted exhaust, low power, dvom chapter 2 switch inputs, digital signals, module communication, hall effect testing chapter 3 transistors, solenoids, computer controlled output testing chapters 4 and 5 fuel trim and oxygen sensor testing. Some injectors will come with a disc containing the unique trim code file. I basically have the same problem with trim values on my truck. Ive owned the truck for two years, and it has consistently gotten 460480 kms per tank about 16. Learn more about scannerdanner s favorite products. To better understand how fuel trim is used to maintain the proper air fuel ratio, look at the set of fuel injectors in fig. Short term fuel trim is what the computer is doing at that time to control the fuel mixture.
When the engine operates at normal or higher load or at higher engine speeds, larger volumes of fuel and air are needed. The ecu controls airfuel mixture in order to maintain power, efficiency, and emissions. Fuel trims are the deviations from the correct airfuel mixture. Note that the injector size will automatically reduce the overall fuel and cranking fuel even if the trims are set to zero. It has to do this a minimum of 2 to 5 times a second. The ecm can only correct for a certain amount, then the check engine light will come on.
Fuel trim diagnosis maintenancerepairs car talk community. Understanding fuel trim is an efficient in automotive emission troubleshooting. Fixed fuel trims analyzing pending lean codes scannerdanner. Understanding st and lt fuel trim was the key to identifying this multiple problem issue.
This is a scannerdanner premium video recorded during my class at rosedale technical college. Really, the oxygen sensors are what drive the fuel trim readings. I think snapon does it, i know the auto xray does not even though i was mislead when i bought it. Positive fuel trim means the computer is adding extra fuel too lean. 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. 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. Information in this document is subject to change without notice. Fuel trims are the deviations from the correct air fuel mixture. As the vehicle runs the trim ratios will vary based on fuel mixture wintersummer blends, temperatures, etc.
I dont doubt it, if you see long term fuel trim pid but dont see short term trim it is likely a software hole. Is there any way to clear the short term fuel trim and long term fuel trim other than disconnecting the battery. Adjustable insulation piercing test clip with bplug inputs. 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. By changing the airfuel mixture from lean to rich is called close loop. Short term fuel trim stft multiplicative this is the control of the injection pulse time open over the mid to upper range of engine operation. The injectors were removed from a 2000 honda odyssey that had idle quality.
The o2 sensors will be the indicator or as one of my students has said, is the snitch of the air fuel mixture. To evaluate the actual trim numbers that the pcm is using add the st to the lt which results in the total fuel trim. Not uncommon to have a 3 times increase in pulse width idle to 2500 rpm. Bank 1, sensor 2 downstream sensor is used to analyse the efficiency of the catalyst by comparing to sensor 1.
In this program jim wilson shows you how to use fuel trim as a diagnostic tool to test certain sensors and to verify your auto repairs. Fuel trim flips to negative to reduce fuel accordingly, fuel to compensate for the leak. Some programming will run and the injectors serial numbers will be inputted, which tells the ecm all of the injection data. The short term fuel trim stft refers to immediate changes in fuel occurring several times per second. Teaching gas direct injection diagnosis with information. Use the information to target the next diagnostic steps. 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.