Quote:
Originally Posted by GregWeld
I hope Jody will add to this -- but VE's are the efficiency of the engine at a particular MAP point... once the VE is "on" -- then you should leave that alone and just change the A/F ratio that you want to run at that spot. Check your O2 sensor readings -- and if the motor is 'putting out' the A/F ratio that you've set and it's not adding/subtracting more than say 5% -- then I'd just leave the VE where it is.
I have Accel -- so it's hard for me to tell you what your screens are... but the Accel has a 'screen' that is similar (I think) to the Fast system - where you can see a scale of what the O2 sensor is doing.... and if the VE is on the money - the O2 sensor is doing 'little'. That would mean the VE would be right on... If the O2 sensor is adding and subtracting 10 or more % - then that should be corrected first. Once the VE is on - then you should be able to change the A/F ratio and the ECU will just simply figure that ratio out and that's what the engine will get.
Does that make sense? Ideally -- you'd want the VE table so well set - that the O2 sensor is just along for the ride. That is not always possible of course... but if the VE tables were perfect - you wouldn't even need an O2 sensor.
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getting the VE's right with the O2's working as little as possible is the goal. But if you change the a/f desired at a particular range the VE will also change to keep it ideal. I treat the VE table like jet sizes, larger numbers are richer and smaller are leaner, so if you change your a/f table you'll want to dial in the VE table as well.
In closed loop the computer will compensate by adding or subracting fuel to reach you desired a/f. You can limit how much it adds or subtracts in the tuning software, usually most aftermarket systems have a max limit of 25% +/-. That means if your VE table is within 25% of the ideal number to reach your desired a/f number, then the computer will automatically add/subtract to get you there. Your job as the tuner is to get you there without a lot of computer intervention, so it still has room to add/subtract fuel due to varying conditions like temps, baro changes, etc.
Jody