thanks to all that helped.
my ltft @ idle is now 0% and my stft bounces around between -3 & 3. I'm going to work on my curise trims now. they aren't too far out of whack, about -6% in the LTFT. Should I use the voltage latency to adjust the cruise trims and will it effect my idle trims much at all?

 

[QUOTE=l2r99gst]
Rescale your injector to be 8% bigger than what you have them at now. That will cause the ECU to shorten the IPW by 8% so in effect you are taking out 8% fuel, which is what your trims are doing right now. That should bring your LTFT for idle to about -2% and your LTFT for cruise to about +2%. That would OK in my book, as you have plenty of adjustment in either direction for both trims.

But, since you're scaling your injectors bigger, this will also lean out the your open loop fueling maps by about 8%, too. So, to get all of your A:F ratios back to what they are now at WOT, you would have to edit your open loop fuel maps so the values are also 8% richer. For example, if you have a a value of 14.0 in a certain cell, you would have to change that to be .92(14)=12.88.
QUOTE]

If the ECU is at +18% for a fuel trim wouldnt that mean it is adding fuel and therefore you would have to scale the injectors smaller to make the IPW increase?

 

Yes.

A positive trim means the ECU is adding fuel. So you would have to scale the injectors smaller to have the ECU increase the IPW, increasing fuel.


Eric

 

Thanks Eric Im doing that today, wanted to double check that I had it right

 

On a "factory" fuel map (well it is an FQ model, but the map is RICHER than stock in the higher closed loop areas, and I've only changed it above 200 load) my low trim is 100, med trim is 109 and high is 100.

There is a Walbro pump and 3" exhaust, and the side cut out of the airbox (which I don't think makes the MAF misread).

Can anyone confirm that the 109 means +9% or +4.5%? The fuel map contains 14.7 down to 13.8 in the closed loop areas, yet it appears that fuel is being added.

Puzzled!

 

Is low, mid, high for load or rpm? Is this LTFT applied to the open loop fuel tables?

 

In Evoscan, 100 would be equivalent to 0% in Mitsulogger or an OBD-II scanner.. Therefore 109 means 4% or so LEAN, so add 4% or so fuel..

I updated the scaling in mitsulogger to show OBD style fuel trims, you can do the same in Evoscan if the current setup is confusing..

The formula in mitsulogger is int(.1961*x)-25 And Evoscan can't use this formula directly, but if you can use something similar, it will calculate a range from -25% to 25% which will closely match the alterations you'd need to make in the ECU..

 

Its closed loop fuel trims.. Open loop isn't affected at all by it. I originally thought the same thing, but after thinking about it and verifying it with a DSM'er we figured out it had no impact on open loop fueling.

 

Thanks Jack.

 

MalibuJack, when you say this was verified, do you mean verified by looking at data or code? Or verified by an expert? Not trying to be difficult, I just want to understand if I can take your statement as fact.

 

There is enough data out there to confirm without a doubt that the fuel trims have no impact whatsoever on your Open loop Fuel tables.

You can take this however you want, but it doesn't change the fact that it had no impact on fueling..

It make sense however, since a bad O2 sensor could force the fuel trims to go out if their trim range, and will not affect the open loop fuel tables at all.

 

MalibuJack, thank you for the clarification.

I found a good description of fuel trims for BMW, but should apply in general for all ecus.

http://theautomotivetechshop.com/con...m.pdf&linkas=4

 

Very good document, thanks for posting the link..

It definitely brings all of the topics we regularly discuss together..