Fuel trims question.....
Fuel trims question..... Probably an obvious answer to this question but....... I have been reading some of the LTFT - STFT tuning documents and understand what to do but have one question that is probably a given but I am confused about.
When I make a log, then copy and paste results to the VE table, then reflash PCM, then go make another logging session: Do I need to "reset fuel trims" before I go out and log every time, or just for the first logging session. Or do I just flash the PCM with the current VE table then go out and log agian? Hope this wasn't to confusing
When I make a log, then copy and paste results to the VE table, then reflash PCM, then go make another logging session: Do I need to "reset fuel trims" before I go out and log every time, or just for the first logging session. Or do I just flash the PCM with the current VE table then go out and log agian? Hope this wasn't to confusing
Ideally, when you reflash the PCM, it should reset the fuel trims to zero. However, it doesn't hurt to clear them out. What you really want to do is give the car a few key on/off cycles before logging. Let the car accept the new settings and make sure you're not logging after a recent trip to the gas station. The evap system can screw the readings.
I believe that the PCM when reflashed does not reset LTFTs back to 0%. But, that is not a big deal. You should always drive the car thru some driving cycle which will allow the PCM to relearn the current correct LTFTs,,, then data log. After I reflashed my PCM, I run my Auto-Tap but do not save anything until I notice that the LTFTs have re-adjusted and have settled down. You must drive a couple minutes in each off the most common visited fuel cell for the LTFTs to fully adjust, lots of time it takes just 1 minute or less per fuel cell. Then I do a data logging session.
Originally Posted by SSpdDmon
Ideally, when you reflash the PCM, it should reset the fuel trims to zero. However, it doesn't hurt to clear them out. What you really want to do is give the car a few key on/off cycles before logging. Let the car accept the new settings and make sure you're not logging after a recent trip to the gas station. The evap system can screw the readings.
Also why should he make sure he is not logging a recent trip to the gas station? How would this effect what he is trying to do, and how can it be corrected?
Just asking to get a understanding, I am to trying to learn.
I've noticed when I'm logging, my LTFT's take a dive by 5~8% after a fill-up. I think there's a vent tube of some sort from the fuel tank to the intake manifold. I'm not sure how it all works. But, I think it has to do with keeping the fuel tank at a certain pressure level. Ever heard of people getting an SES light because they didn't put the gas cap back on right? I'm pretty sure it's all related...
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