The short term fuel trim stft refers to immediate changes in fuel occurring several times per second. Are you positive that clearing codes with obd2 scanner resets ltft. You set your obd2 to graph shortterm fuel trim over time and then you spray either the propane or the carb solution near the suspected vacuum leak point, while observing the stft graph for a sudden and strong deviation. Obd2 scannerdongle for stft and ltft hyundai tiburon forums. Positive fuel trim percentages indicate that the powertrain control module.
Obd2 eobd2 diagnostics blog fuel system monitor stft ltft what diagnostic code reader scanner should i buy. If the ltft is higher than 10 either way, it may indicate a problem. Using the wrong process while scanning your vehicles systems can cause the readings to be inaccurate. Unlike many scanners you can pop your phone on to the windshield and monitor things. Stft and ltft means short term fuel trim and long term fuel trim and what the numbers are saying is that on bank 1 there is a problem and its running rich, bank 1 cus u have a v engine there are 2 banks, bank 1which is usually the left side as u look at the engine has somthing like a 02 sensor fault air leak injector fault, really u need to look at the live data of the 02 sensors to see what. How to read live data from obd ii scan tools scanneranswers. The stft, and ltft, and 2 oxygen sensor voltages were available. If it is a bad injector or o2 sensor, then i have to explain why both sides track pretty well in both ltft and stft. Baselining the fuel trim data is a simple fourstep diagnostic process. Stft will normally sweep rapidly between enrichment and enleanment, while ltft will remain more stable. If the mixture is off enough so that ltft reaches the limit of its control and still cannot correct the condition, the stft would also go to its limit of control in the same direction. By now you should see the benefit of monitoring fuel trim values and will begin the process of using the fourstep fuel trim procedure.
It uses sensors to measure or calculate airflow, consults an air fuel. Multiplicative mixture correction 1 is ltft in obd ii generic and will change only during cruising speeds. My younger son took his bmw to a local place that specializes in that sort of thing. Ltft refers to changes in stft but averaged over a longer period of time.
If someone can help me solving a lean condition issue, id appreciated. Understanding stft and ltfl in automotive nguyen hieu s. In a perfect world, the stft would read 0%, ltft would read 0%, and o2. This short video will show you how to get your fuel trims under control when they are off more than 23% using hp tuners 3. Bmw and mini longterm and shortterm fuel trim diagnosis. Obd ii generic data contains more than enough information to solve many. Elmscan 5 compact buy the elm327 based obdii scan tool. Since the driver controls airflow load with the accelerator pedal, the powertrain. Generic elm327 scan tools do not support mscan, but will provide access to. Fuel trim diagnosis maintenancerepairs car talk community. Graphed data is very useful but it can be shown digitally too.
Whats about short time fuel trim and long time fuel trim. There are often questions asked on the forums about fuel trims and ive even had a few emails requesting clarification. Global obdii fuel trim reporting was standardized for all manufacturers in. Generic obd2 the features that are supported by most obd2 software applications on the market provides access to. Ease verification tester with can support created date. Short term fuel trim stft the correction factor being used in closed loop by the pcm to maintain a balanced fuel mixture. When reading live data from any obd2 scan tool, it is best to always check the stft. Well, i have worked very hard to make a definition file that works well with tunerpro, and here it is. Interpreting generic obdii scan data obdii resource. I have a basic innova that shows me codes but nothing else. These three variables in the fuel calculation stft, ltft and. I like to see stft go from positive to negative rather than staying positive. Ltftstfttension of lambda 1tension that must reach the lambda 1. To check the low oxygen sensor range, simply create a lean condition and check the voltage.
Typical causes for a change of offset type stft ltft idle mode. The software has all of the standardgeneric obd2 pids available. This is 2 important definitions in automotive engine control and diagnostic. In this case, the ltft will continue to change until the stft becomes balanced. Having wideband data is often preferable to hegostftltft. As with ltft, the number should usually be plus or minus five. Changes in o2 sensor voltages cause a direct change in fuel. Tunerpro is a software package designed for the diy tuner.
I am looking for a windows based obd software, which would mainly be used on smart. The ford enhanced diagnostics addon is designed to work with any scan tool that is based on the elm 327 command set. Ltft may show a noticeableltft may show a noticeable impact as a result of the single cylinder ignition misfire rangingcylinder ignition misfire ranging from single to dual digit positive values. If theyre in the percentages, it means the computer is seeing a rich condition so it adds less fuel to the engine by decreasing the pulse widths of the injectors. As reference, bank 1 looks normal, i see stftltft going updown single digit mostly. Stft and ltft are expressed as a percentage, with the ideal range being within 5%. Enhanced obd2 diagnostics enhanced diagnostics provide access to oem level diagnostics that are not available over generic obd2. About 67 months ago, i bought a kiwi obd ii reader, simply out of curiosity as i am a computer guy and a geek and was curious about various ecu numbers and wanted to see how the car was doing. Go here to read the latest obd scan tool software testing. Is it possible to monitor the long and short term fuel trim values with the obd2 module. This is how much fuel the computer is adding or subtracting. Once the longterm trim is in place, the shortterm continues to operate and go positive or negative as needed past the standing longterm trim. Diagnose your vehicle, read and erase trouble codes, measure performance,and much more.
If the fuel system is open loop, 0% correction should be reported. Connect an obd ii generic scan tool, preferably with recording capabilities. The fuel system monitor is a program within the powertrain control module. Additionally, before reading your vehicles trouble codes, youll need to know how to get the process started.
This is when i noticed very strange ltft and stft values and have been pretty much going crazy trying to diagnose what might be going on since then. Octech, llc strives to provide you with a onestop site for obdii scan tools and the most userfriendly software on the market. Just trying to get full use of a obdii scanner i have just bought. Are there perhaps different methods scaners use to clear codes. Obd2 eobd2 diagnostics blog fuel system monitor stft ltft. The obd2 protocol suite isnt very fast by nature, but i was able to pull several pids per second on the above mentioned cars. Checking oxygen sensor speed is where a graphing scan tool helps. B1s2 catalyst temperature command secondary air status. Stfts between two banks are almost identical and are almost always positive, meaning ecu is adjusting for a lean condition, which by the way should be normal since i have an aftermarket cai that is obviously allowing much more air into the engine causing more fuel to. Ran a obd2 scan alittle while ago and i got 2 readings with stft b2 s2as well as stft b1 s2 stayed constant at 99. At idle, the ltfts are a little lower, but still off, around 2.
Stft shortterm fuel trim and ltft longterm fuel trim. In practical terms, obdii is the complex web of sensors, computers and. I would like it to show stft, ltft, o2, map, ait at a good refresh rate. It is heavily documented with comments, and all of the parameters are categorized.
Explains how to use the obd2 or obdii scan tool and how to interpret the data. One of our staff is a specialist and averages over 5 diagnostics per day. Is the fuel sys1 and fuel sys2 information helpful when looking at realtime datastream. The long term fuel trims ltft are driven by the short term fuel trims. The misfire detection monitor, a software strategy built into the computer, is designed to detect an engine misfire. Im having a hard time deciding on which obd2 scanner that will allow me to monitor my openclosed loop settings and my stft and ltft. Short term fuel trim the pcm uses the stft short term fuel trim to help switch the o2 sensor from rich to lean and back again. With this, i was able to graph the data onto a spreadsheet and quickly make charts and graphs with mac numbers, and or microsoft excel. Finding a vacuum leak and performance issues using fuel trim data.
Thats why i am starting w fuel filter and fpr, although i am tempted to go ahead with the full injector ultrasonic cleaning and testing. My forester is my2000 and doesnt have an obd2 protocol as you know. The fuel monitor run 2 software programs, 1 stft short term fuel trim, 1 ltft long term fuel trim, both of these monitor the fueling of the vehicle and try to keep. Scanmaster obd2 scan tool software, provides professional quality diagnostic obd software for all obd2 compliant cars and light trucks. The job of the stft is to keep the o2 sensor switching above and below 450 millivolts by increasing and decreasing the injector pulse width. While on idle, obd2 continuously read stft short term fuel trim high at 10 to 30%, again with similar numbers for both banks. Since the driver controls airflow load with the accelerator pedal, the ecu can only control fuel. Both the stft and ltft have limits which vary by calibration. There are a bajlillion on ebay and honestly im not sure which one would work best. The mondeocontour in europe has only two o2 sensors. Im cleaning the maf sensor for the second time, this time more thoroughly with isopropyl alchol as well as spray, just in case. I bought a 2002 ford focus ztw zetec, at 100k miles a month ago, and i noticed obd2 always reads ltft for both bank 1 and 2 reading pretty high at 1025%. When monitoring obd ii generic data parameters, youll notice that stft and ltft will react independently in the different operating ranges considered here. So the vacuum leak is wherever you elicit the suddenly altered stft value.
Interpreting generic obdii scan data obdii software. After 5 minutes of idling, the engine stopped by itself. This obd2 spy scan tool software achievess communications speeds of 128,000 baud on a 91412 protocol vehicle using our 2x80s usb scan tool. It is free, and requires a definition file to work. Stft may show a minimal impactstft may show a minimal impact as a result of the single cylinder iiti ifiignition misfire. Understanding obd2 live data is a lot easier than it might sound, but there are a few things you need to know first. It does one thing, edits bin files, and it does it very well. Im still working with it, but i was also able to downloademail the live data to myself. Using the longft1 and longft2 dual bank engines pids the longft12 pids are useful for diagnosing fuel. Becouse it looks just like ecu was learning from stft and gradually correcting ltft map. The good news is the recent phasein of new parameters will make obd ii generic data even more valuable. When observing the fuel trim data of a vehicle for diagnostic purposes, the. Additive mixture correction 1 is stft in obd ii generic and will change only during idle operation.