Nistune Forums

Hi All,
I'm very new to the whole tuning scene so I will apologize ahead of time if I don't make sense or if I seem like I don't understand.

Currently I am in the market to tune my engine (RB25) strictly for the sole purpose of achieving better fuel economy/MPG. Honestly I don't really care about WOT #s as I never even hit WOT and mainly drive city driving partial throttle as this is my daily.

Now here's where it gets a bit tricky for me and the reason for starting the thread. When in closed loop the ECU will read the o2 and determines if the AFRs are too rich/lean and then compensates by either adding more fuel or reducing fuel to get back to stoic 14.7:1. What I'm wanting to try and tune for is running a leaner AFR at cruising speeds so in theory using less gas (someone around 16-16.4 AFRs).

Now, does NIStune somehow let you tweak the lambda feedback in closed loop so the ECU doesn't try and bring it back to 14.7 when I actually want to run leaner? I currently installed an AFC-neo and def not pleased with it as the factory o2 just "overrides" my settings in the afc as it brings it back to 14.7.

I will NOT be tuning the car myself but a reputable professional tuner will be. I just wanted to get the information answered before I go out and purchase it like I did the afc and have it still not do what I desire.

I hope this makes sense,
Thank you so much.

Adjusting the 02 feedback reference voltages (upper, lower thresholds) in nistune will change the reference centre of Lambda for the chosen fuel.
The ecu will then adjust between the new thresholds, calculating a leaner result.
May also need to run idle in open loop so a smooth idle can be maintained.

personally, I don't think any reputable tuner would do this as it causes higher emissions of other greenhouse gases and could cause premature failure of some engine/exhaust components in the long term.

so a little leaner mixture on the highways causes more gasses?? I wasn't aware of this myself??

I too would like a leaner mix when crusin down the highway to save mileage and petrol(that should even out the harmful gasses right??)

ive only gotten so far as to get 15.2-14.2 in terms of highway afr with nistune. so to the o.p. yes you can adjust the afr with nistune(and see results).

The catalytic converter works on stoichometric gas ratio for optimal conversion of exhaust gases to Co2. Leaner mixtures are documented to affect its operation and result in worse emissions

ah, but iam not running a cat. just 3" straight through.

Might want to do some reading up on how catalytic converters work
http://en.wikipedia.org/wiki/Catalytic_converter

They turn the harmful gases into Co2. If you are not running a cat converter then you are putting toxic gases into the atmosphere and subsequently fail emissions tests if you were tested

I too would like a leaner mix when crusin down the highway to save mileage and petrol(that should even out the harmful gasses right??

There will be no evening out without one of these, despite your mixtures.

Basically NOx goes through the roof after you passed Lambda 1