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VE Tuning and Reseting Fuel Trims

JoshMcMadMac

JoshMcMadMac

New member
I have started with VE tuning the car. I have read conflicting opinions on reseting the fuel trims. Everything says to reset the fuel trims the first time. From there I have read not to reset the fuel trims after updating the table and starting a second scan, basically not reseting the fuel trims again throughout the iterations of VE tuning. On the other hand I have read that it is necessary to reset the fuel trims after every update to the VE vs. RPM vd. MAP table, along with a decent drive and a few restarts in between. I have been getting a good LTFT scan in SD mode on my drive to work, updating the table in the editor, uploading the new program, then getting another LTFT scan on the way home, updating the table in the editor, uploading, and repeating the following day. It appears to be closing in pretty well, but I am wondering if it would be better to reset the fuel trims and give the car "learning" time between scans/updates.
 


In Jerry's tuning guide, he says anytime you change anything fueling related you should reset them. IIRC, the VE table is under fueling, so you should probably reset them.

Side note, I'm debating if I should do one. Most of my LTFTs are about -3 to -4.
 
Unless I do some MAJOR tweaking to my fuel, I don't bother. Like say I'm adjusting the MAF in a certain range, I leave it alone. If I'm doing a full VE tune, I will reset it.

If the car already has learned the trims, and you know where to change them, I just don't see the need to make it completely relearn everything......it wastes gas and anymore I just can't afford to burn through a full tank of fuel for minor tuning.

Just my opinion, take it for what you will.
 


JoshMcMadMac said:
I sure have. This tuning stuff really just turns to pudding when you try to figure out what other folks do...no one can seem to agree on anything. :th_tongue2:
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I agree with you. It is really tough. One thing to note, is those that do tuning for a living has to do it the best, fastest, most accurate way possible. Seek those people out for answers.

Since you are on the HPTuners forum, ask Russ what he thinks about this subject. He is one that has been in the automotive business since 1976 and very willing to share info, and yet has people drive for hours to have him tune their vehicles.
 
Bringing this back up...so when the fuel trims have re-learned, should the LTFT become steady as opposed to "moving" up or down in value as I hold that point?
 


When at idle, they will constantly fluctuate. the goal is to keep them in a certain range from zero. Example would be -3.0 to +3.0

If you get a good tune going, it will be closer to +/- 2 or lower. It's simply impossible to keep it at 0 all of the time.

WOT is different because you want them to lock at 0 in PE mode.
 
Reptile said:
When at idle, they will constantly fluctuate. the goal is to keep them in a certain range from zero. Example would be -3.0 to +3.0

If you get a good tune going, it will be closer to +/- 2 or lower. It's simply impossible to keep it at 0 all of the time.

WOT is different because you want them to lock at 0 in PE mode.
Click to expand...

I "deduced" that idle would cause the trim to go up and down, and it is nice to hear reassurance on that. I am getting the trims close, like you mention, but I am asking if each point, say point X,Y is at -2, and I hold the engine at that particular point for an extended period of time, should it remain at -2 or could it change?
 
Over time they will "learn", but it's not an exact science. This is where a VE tune comes in pretty handy, and also why it takes so freaking long to lock in a VE tune. Unfortunately it's not always going to be dead on, just get it as close as you can. Because as soon as the temperature/humidity goes up or down, it's going to be off. Technically, the car you drove to work this morning will be a different animal in the heat on the way home.

It's a never ending deal, but this is where you learn what settings your car likes best. So you can get a feel for it.
 
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