Dirtee wrote:[quote:cafe6a0914=VRX_Pete]I think the manual says 15 mins, should be more than ample. Enough to reset the ECU to re-learn your driving style and adjust the maps/profiles accordingly.[/quote:cafe6a0914] Doesnt affect the MAPS that were put in by a tune right..?
disconnecting the battery will reset the long term and mid term fuel trims which are used in closed loop operation - normal driving - the closed loop AFR for example is 14.7 so regardless of whats in your map, tuned or other wise, its going to tell the injectors to "add" x% so that you hit 14.7 when driving in closed loop, cruising etc - which is determined by the mass airflow sensor.
Now for the stock ecu/tune, LT fuel trims do affect wot afr - so when you punch it, the car will use your maps but will also adjust fueling based on what it had to do to keep things happy while cruising.
So if you got tuned and your fuel trims where +/- 5%, you then reset the ecu, you'd see a bit of difference (either rich or lean) for i think its 20-40min before the fuel trims returned to where they were. which they should assuming you didn't modify anything in between. So you wont be losing your Merlin tune Tim!
Simpler way to reset the ECU is to pull the ecu battery backup fuse
I agree though, if you change the exhaust, either resetting the ecu or driving the car for a day, you'll end up in the same place ecu wise. Yes the car will adapt to it for closed loop idle and cruise, but its not going to tune itself for the rest of time when your accelerating etc.
To the point about exhaust/intake flow,
Stock amount of air in is lower than it could be due to the stock exhaust.
You could have the biggest fanforced turbocharged soup'd up intake but if that same air cant leave the engine via the exhaust, the whole thing backs up. By opening up the exhaust, you unlock the potential air that could be going through the stock intake. Since the stock tune (fuel maps) are typically super rich (more fuel than air) by you opening up the exhaust which inturn opens up the intake/overall air flow, when ecu gives its instructions to all the mechanical systems (injectors etc) to get a AFR of say 9, its going to get that extra little bit of air so the actual AFR will be more like 10. This is why most intake/exhaust upgrades give that power benefit without really even needing a tune! Sounds pretty good! But imagine if the car was/is tuned at the limit and you then added on a exhuast!