I think that fooling with cheaps resistors complex control systems will only improve the budget of the seller.
I think that ECU eco tuning it's Greenwashing
Greenwashing - Wikipedia, the free encyclopedia most of the times.
I did several high precision data logging sessions measuring fuel consumption with a 0.05 L/100 km precision, and never got any saving.
I have a lot of data and I decidet not tu reflash a fleet because of the results.
Savings are only noticeable depending on gearing and in high slope roads or full weight capacity towing or loading.
The high precision tests needed to obtain optimal fuel consumption and minimum BSFC I think there are no chiptuner that invested time or money enough to develop a scientific research or a scintific independent assesment to ensure the consumer that it's all true.
I know it is possible to obtain little improvements if you don't matter emissions regulations of CO, HC, PM, NOx,... but I have not found any chiptuner that can explain why their new numbers in the ECU will save fuel (according to physics, engeenering, R+D assessments,...). You will get hundred of words, the more you ask the more you will not understand (or, if you have enough sci-tech knowledge in the matter, the more disappointed).
I got coherent savings results in ABA testings when I improved driving techniques, aerodynamics, tires, gearing, repaired thermostat, and sensors who where not precissely tuned or fooling the ECU.
I will appreciatte if anyone could post a BSFC map of a tuned engine. I did not find one.