91 octane gas here is already $3.85 a gallon and rising.
We decided to do some test and tuning to see what can be done to reduce gas costs but still have fairly little loss in performance or damage due to ping
We had a perfect day as worse case weather in that temp was 85 degrees, winds of 19, gusting to 29 MPH.
Testruns were done at elevations of 3,600 to 4,000 feet.
Keep in mind the engine in our 1999 C5 has 11.3:1 compression so it would be more prone to engine ping/knock.
Also made use of is our water/methanol injection.

Starting with end results.

If we believed the forum hypes to have a perfect tune you must have the LTFTs at part throttle rich (negative values) in these test results shows that is bullshit.
On the left we have results were the LTFTs are rich and on the right side results we tuned to be about 10% leaner and you'll notice the injector duty cycle was reduced from 70% to 59% which means not only are injectors not working as hard but also flowing less gas but overall in in high engine loads the gas saver tune only lost about 15 HP at flywheel.
For daily driving then tuning to be leaner will save a lot of gas costs long term for very little loss of performance.



Here is testing where on left we set for 5% leaner and then on right is for 10% leaner and notice there was no real performance loss at all at the required injector size needed is reduced.



Here we can see the OBD-II realtime data where was see what little ping there was when the water/methanol injection came on the ping instantly went away and also due to the tune the attack and decay rate of ping is very quick.



Here we see even when there was ping that timing only decreased less then 3 degrees



As the weather changes people also change the type of clothes they wear so its the same thing for your car is to have different tunes for the type of driving you'll be doing. With our PCM flash tool which is $200 less then a single user tuner tool you can switch tunes within less then 5 minutes of your time

In the end the city MPG went from 18 to 21 ( about a gain of 51 miles more per tank of gas)
and highway from 31 to 33

Please explain me something:
in closed loop the PCM is constantly adjusting the fuel trims to maintain a Lambda value = 1 (stoichiometric).
Why should we have a lower fuel consumption with positive fuel trims? No matter what the trims are the PCM will still aim at Lambda = 1.

I belive you about the positive results, but why does it need less fuel? (-10% in average, that's A LOT!)

The PCM is not maintaining a strict 14.7:1 AFR but within a window EPA allowed.

If it was STRICT you'd see 450 mVolts average of front 02s all the time for what your calling "closed loop" is really PCM has 7 modes of operation and as long as the EPA window is met that all the PCM has to do.

Thats clear in that the short term fuel trims window is being met then the long term values are ignored.
Decel would be in closed loop and clearly the PCM would not still be trying to maintain stoch when getting off gas pedal thus fuel trim could go as much as +23 before tripping a lean DTC.

DO not forget the stoch value can be changed in the PCM so what would happen if it was changed to like 15.2:1 ?

Some facts:

My WB is showing an average of 14.9 (hopefully it's precise). No matter if fuel trims are positive or negative.

When my fuel trims (LTFT + STFT) are positive (average +2%) I do see a lower fuel consumption (5% less). This only on long trips on the highway.
For short trips (like daily home to work during 30 min) the consumption doesn't change.

During decel the WB shows an AFR of 12.5 - 13, LTFT are around +4% (cell # 21)

Your comment?

Can I really chenge the target AFR??
I never touched this value (LS1Edit). I was thinking that was something not to play with...

I have changed the AFR target and see leaner O2 reading. Keep in mind though in tuning for a biased for better MPG, it is not just the fuel flow being reduced but also functions like timing.

My last tests yesterday increased MPG in city from 21 to 24.

Due to engine mods, where car is located, if water/meth is being used fuel can be saved which of course some hit to performance but the goal is to have multi tunes and when the need is to save on fuel costs to run a tune biased for it.

What is a safe target for a leaner AFR? You mentionned 15.2...

It would be interesting to set different AFR targets in a map similar to the VE table.
I know that it's feasable for different European or Japanese cars. What about our cars?

The PCM allows up to +23 fuel trims before it trips a DTC.

Lean cruise is a much as 17.0:0 so it should be easy to dial in a 14.2 with most NA setups for non performance drives like when cruising or low speed trips

You mean 15.2 right?

What about the catalysts? will they suffer because of the different gasses combination?

Yep sorry, 15.2

If COT is tuned correctly PCM would still protect the CATs if they got too hot