Originally Posted by tfnaaf
Well, im deffinately a N00B when it comes to e-manage tunning for sure. But if you have the tiem could you possibly explain How to tune by watching the fuel trim?

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.