turboengnr

iTrader: (2)

Alright. I know there was a thread about this before, but it was all jumbled up over the course of 3 pages. So i am just doing this to get all of the information inside of 1 post.

Also, this only effects piggyback computers (emanage, split second, SAFC, etc)




it will compensate +- 20%

It only compensates at part throttle. When you got WOT, it takes the last known correction, and locks it in. So if you are cruising, and the correction is -15%, then you punch it, that value is locked in. So you are losing fuel and running leaner.

But the opposite is also possible. It can run very rich by adding up to 20% at times as well.

This is why people's dyno graphs are always different.

You have to tune each individual car for fuel trims, keeping them as low as possible at all times. Once you do that, you will have more consistent fuel curves.


you have to use a scanner to look at the long term and short term fuel trims, and spend hours screwing with fuel settings to try to get the fuel trims as close to zero as possible. While screwing with the fuel trims, do not tune using the wideband. While at part throttle, give the computer the a/f it wants. It is normally safe to run it a little leaner while you are only under partial load. When you go WOT, that is when you need the fuel. And thats why you have to get the fuel trims right.


you tune with a wideband at WOT. If you use a wideband to tune at part throttle, the computer will compensate and adjust the fuel to where it wants it. Then when you actually do to full throttle, the value that the computer has locked in will transfer over to the WOT setting, and it will mess with your tune. The computer has a "fuel trim" feature that can add or remove 20% of the injector pulsewidth. That means that if you are running an a/f ratio of 11.3 on one pass (lets say the fuel trim was at +12% this pass), then the next pass could be in the mid to high 13's with a fuel trim of -20%.

You have to tune the car under ALL LOAD AND ALL RPM VALUES! If you do not do this, then you will most likely have fuel trim issues.




no prob

it is actually quite simple.

you need some sort of OBDII scanner that has a data streaming capability.

When you have that, set it up to watch the LT_Ftrm and the ST_Ftrm (long and short term fuel trims). When you have that, you need to have your laptop setup to watch your fuel tables in real time.

When you have those set up, you need to start cruising at low RPM (around 2k) and then start accellerating with a specific amount of throttle. You then watch both the fuel trims on the scanner and the fuel map on the laptop. When you see the fuel trims start to add or subtract fuel, you do the same on the fuel map.

so lets say you are at 3250 RPM and the scanner shows a LT_Ftrm of -2% and a ST_Ftrm of -14%. You should gradually take out fuel in the fuel map until the fuel trims come back down to around zero.

The difference between the LT_Ftrm and the ST_Ftrm is simple. The ST_Ftrm's are what the computer is doing at that specific point in time. The LT_Ftrm is the trend that the computer is seeing.

You know how they say your computer "learns"? Well, they are talking about the LT_Ftrm. Over time, the computer averages out the data it recieves and outputs it as a single variable (LT_Ftrm). When this is at or close to 0%, that means that you spend most the time with a 0% fuel trim correction factor.

When you disconnect the battery, this is the value that gets erased and must be "re-learned" in order for the car to run at its potential.

Typically i like to see fuel trims between +5% and -5% on the LT_Ftrm.




no, because when you disconnect the battery, it automatically starts learning everything. It then programs the long term fuel trims and updates is constantly. It can change the long term every second or more within the first few minutes of driving.



because you can still tune at WOT. You just need to have the proper tuning during the non-WOT part of the map.

once you get the fuel trims dialed in, you will have an extremely consistent a/f curve.




to make it relearn correctly, drive the car like you normally do.



leon, you are partially correct.

But one aspect that you need to look at is what a/f ratio the car is looking for under load. I know when i was at ~75% throttle with my car NA, the car ran in the mid 12's a/f. The car knows when it needs to be lean and when it needs to be rich.


The problem with resetting it every few days is this....

when you let it learn everything, it takes a while for anything to change the LT_Ftrm's,. When you reset the ecu, it updates it constantly.


but as long as your ST_Ftrm is constantly out of a desired range, then you need to tune to bring those within the limits.

turboengnr

iTrader: (2)

mods, you can link this to the turbo FAQ instead of the old thread. Then just close this one. I just wanted to make it easier.

TheSmuggler

iTrader: (11)

Ok, stupid question Mike... If we got a standalone like the AEM ems, would that allow us to forego the headaches of the +-20% deal, or would we still have to go through the same process as above.

turboengnr

iTrader: (2)

with the AEM you can program in how much fuel trims you want. So if you dont want any fuel trims, input 0%. If you wan 50% fuel trims, add 50%. Then the computer will compensate up to 50% duty cycle.

TheSmuggler

iTrader: (11)

So, for Daily driving then you would want 0% trims so it dosen't try to trash my A/F then right? Or am I a complete idiot.

turboengnr

iTrader: (2)

well, you will get better fuel economy with the fuel trims turned on.

TheSmuggler

iTrader: (11)

But stability would be better (less cahnce of detonating) when the trims are at 0? Sorry to keep trashing your thread...

turboengnr

iTrader: (2)

it would just allow the computer to adjust. I am not sure if it locks in the values when you go WOT like the stock computer does. I would assume that when you go WOT with the AEM the fuel trims would drop to zero. Atleast thats what i would want it to do.