I was looking at the install guide for some of the Cold air kits and they say to disconnect the battery so that the ECU can relearn the "new air flow"
..
do you really need to do this? and is there a way to do an ECU reset with out totaly killing ALL power to the car and losing all stored settings?
thanks

 

I never did that and my C6 had no problem adjusting to my CAI. It never said to do that on my Xclerator CAI and I am sure MTI knows what they are doing. On the other hand, all you have to do is reset the windows, it doesnt loose other stored settinngs.

 

I think what they are trying to do is clear the Long Term Fuel Trims (LTFT). If you do not do this, they will eventually learn the new airflow, but it will take longer.

 

True, but it takes less than 10 miles of driving for my car to relearn its LTFT's.

 

How do you know if it has relearned on its own?

 

You'll get a relearn grade card that comes out the glove box. haha...just kidding. Just check your mileage,,,after 100-300 miles, for sure it was relearned. You need a HP Tuner scanning to actually reset fuel trims on the fly and can also use it to read the LTFT numbers. Still, its a lot cheaper just to drive the car for awhile.

 

It takes way longer then that and that's with a wide variety of loads... More like 100+ miles.


Mike

 

Well, my judge of the LTFT's learned is by if your STFT's are near 0. That takes me around 10-40 miles and less than an hour.

 

It is subjective to the cell you are trying to learn. Idle will learn almost instantly. Other cells might almost never get hit even in 100 miles depending on how you drive.

 

Actually, the PCM is constantly learning and making corrections. These correction factors are stored in tables based on RPM x Manifold Absolute Pressure (MAP) which is the roughly the amount of air being consumed or engine load.

STFT are corrections based on O2 sensors feedback compared to the PCM target or "commanded" A/F ratio including corrections for various things such as: LTFT corrections, inlet air temperature, barometric pressure, coolant temp, cat over temp, and many others.

When so many corrections or "counts" are accumulated in a particular STFT cell, the PCM transfers the correction to a corresponding cell in the LTFT table which is saved and referenced going forward. The PCM does not save the STFT correction factors for any length of time. That's what the LTFT table is for.

When you disconnect the battery, all the cells in the LTFT table are reset to zero so the PCM goes thru the whole process again using STFT corrections at various engine RPM and load, which after so many counts, is transferred to the LTFT table.

For all the cells in the LTFT table to be fully populated with correction factors, the engine must accumulate sufficient counts over the full range of RPM and MAP or engine load. Keep in mind, when you go over a certain % throttle at certain RPMs, the PCM goes into WOT mode and references the Power Enrichment (PE) table thus does not reference the STFT or LTFT tables.

If it were my car, I would not disconnect the battery. Let it learn and adjust the LTFT table by itself. Some cells like idle and cruise will learn in a few minutes because they will accumulate the number counts quickly. Other cells not as commonly used will take longer to accumulate the number of counts. For example, if you run 200 miles at a constant 60 mph on level ground, your STFT will have sufficient counts cells between 1400 - 1600 rpm which it will transfer to the LTFT table. So you have to run the engine over a wide range of loads (throttle positions) and RPM for the STFT table to get sufficient counts which it will then transfer to the LTFT table. So you might as well just drive it like you normally do for a tank of gas.

I tried to keep this answer simple and easy to understand so have I have not included EVERY piece of information. Since you only made a minor change, even if you did disconnect your battery, you will be OK. The PCM will relearn.