Stopping the fuel trims affecting WOT fueling
Thank you sir...I just read your knock thread...Damn that must have been scary to hear. I was tuning an Evo 9 once that knocked to 36 counts due to a failing fuel pump. Scared the crap out of me. I hope the HFC was the source of the problem.
Newbie
Joined: Jun 2010
Posts: 3
Likes: 0
regardless of how the st and lt fuel trims are affected...during WOT operation the computer goes into open loop operation which means it is ignoring the o2 sensor and IS NOT GOING TO MAKE A ST/LT FUEL TRIM CORRECTION if your car runs like **** during WOT operation either your car is not coming out of closed loop operation like it should or you have a fuel delivery problem that is restricting fuel under serious load conditions. There is no reason to change your fuel trims for performance.
regardless of how the st and lt fuel trims are affected...during WOT operation the computer goes into open loop operation which means it is ignoring the o2 sensor and IS NOT GOING TO MAKE A ST/LT FUEL TRIM CORRECTION if your car runs like **** during WOT operation either your car is not coming out of closed loop operation like it should or you have a fuel delivery problem that is restricting fuel under serious load conditions. There is no reason to change your fuel trims for performance.
Think of it as a "trim" off the fuel map. Example if you LTFT is -2, it will run that much leaner then your fuel map at WOT if you still have the factory trim hz settings.
The 8 and 9 did this as well but was not as sensitive to it as the Evo 10 is.
I suggest you do a little more research before making first posts like this.
- bryan
Newbie
Joined: Jun 2010
Posts: 3
Likes: 0
unless your car is from the planet Jupiter, the PCM is not going to look at fuel trim during WOT, on a scan tool fuel trim numbers are going to change, but the PCM is not worried about where the FT is at. The last time i checked fuel trim is used for fuel correction based off multiple PCM input sensors only during closed loop operation. Modded or not i hope to God your computer is not making corrections on fuel trim at WOT. You obviously are obilvious to open/closed loop operation. During open loop your computer ignores o2 sensor input, i dont give a damn what you say. Why do you think a car runs in open loop when the car is cold?? Because a cold car needs a Richer A/F ratio and it does NOT want the o2 sensor to pick up on it and make a fuel correction. Same crap during WOT when you go WOT you go lean at first but then a very rich A/F ratio, you do not want the PCM to correct that either so the PCM does not look at the o2. No o2 sensor = no fuel correction. and first post or post 23902392032039 who gives a ****. So instead of flaming me and tearing me apart, just tell me where you get the idea that your car still looks at FT during WOT. if your car really did look at FT during WOT you would not be doin this "mod" you would be callin up the lemon law hotline cause your car would be running like absolute garbage.
Evolved Member
Joined: Apr 2009
Posts: 536
Likes: 0
From: US
Do you realize you are arguing with one of the best evo tuners around (GST)? I agree at WOT, the car goes into open loop, and the fuel trims do not change. However, the last saved long-term fuel trim does in fact get used to alter the fuel map tables in open loop. For example, if your LTFT is at -5%, then your open-loop fueling will be 5% leaner than the fuel map tables would normally indicate. This has been verified by numerous tuners and end users for the evo x, hence why this thread exists.
Also, if implemented correctly (such that it were more stable), having fuel trim affect WOT operation does make sense in some contexts. For example, some parts of the country will switch between E0 and E10 fuel during various parts of the year. If the car learns that the recent fuel makes the car run leaner than expected, then long-term fuel trim will be positive. This will then cause WOT fueling to be richer than normal to compensate for the leaner burning fuel.
I agree at WOT, the car goes into open loop, and the fuel trims do not change. However, the last saved long-term fuel trim does in fact get used to alter the fuel map tables in open loop. For example, if your LTFT is at -5%, then your open-loop fueling will be 5% leaner than the fuel map tables would normally indicate. This has been verified by numerous tuners and end users for the evo x, hence why this thread exists.Also, if implemented correctly (such that it were more stable), having fuel trim affect WOT operation does make sense in some contexts. For example, some parts of the country will switch between E0 and E10 fuel during various parts of the year. If the car learns that the recent fuel makes the car run leaner than expected, then long-term fuel trim will be positive. This will then cause WOT fueling to be richer than normal to compensate for the leaner burning fuel.
Last edited by LaXGSR; Jun 7, 2010 at 12:22 PM.