I've been following the ongoing Flashpack iniital impressions thread:
https://www.jk-forum.com/forums/modified-jk-tech-2/superchips-flashpaq-jk-initial-impressions-80188/

which has lot a got input, but I did not want to hijack that thread.

I read about the 3.8L engine awakening before I acquired my 4dr Sahara JK so my initial power expectations were tamed. From day 1 I have been a lot of attention to the engine behavior and the average MPG indicator, maybe too much, it's like watching the kettle boil water.

I had to drive home a couple of hundred miles from the stealer so I had several hours of watching the engine break in a couple of months ago. The JK drove like it was 4WD high and started with an MPG of 13.8. The avg MPG climbed to 19.0 300 miles later. I thought that was great until I never saw that MPG again. After a couple of weeks MPG was at 14-15 no matter how fast I drove and performance was sluggish.

For labor day I drove out to the desert for some light trails and on the way back ~100 mi, mileage climbed up to a steady 18.2 MPG. For the next 2 days the engine felt awake, shifting was smooth and MPG never dropped below 18. Then my 3.8 little buddy started to remember its evil ways and a couple days later I dropped back down to slug mode with MPG in the 15 MPG range and falling.

My liitle buddy seems to run better in hot temperatures, which tells me that the ECM is running the fuel system on lean side. I expect the engine to have a break in period and the ECM to learn the environmentals of where I drive and how I drive, but I don't understand why the ECM seems to revert to day 1.

I will be adding lift+35's+5.13s soon.

Will this send the ECM back into a schizophrenic state during break-in? Or will provide the nurturing guidance the 3.8 so desperately needs?

Should I wait until I reach a certain mileage to buy the Flashpack since it reprograms the ECM?

Also, any insight into WTH the ECM is doing would be appreciated? We are not talking about a highly tuned engine here. I reportedly have 202 ponies and I want all them in their corral waiting to be unleashed at will.

 

i dont know if i can help you any but it seems like my jeep does the same thing.. the only difference my jeep seems to change to whatever driving style i am in, if i am driving fast and accelerating hard the engine seems to feel more alive everytime i drive it, conversely if i am slow poking around and babying it the engine is much more docile. I got my flashpaq and reprogramed my ecm with only about 4000 miles on the engine so i dont know if that has anything to do with it or not....

 

Actually, when I think about my seems to do the same thing, but the response is not immediate. If I drive patiently and don't open the throttle too much, the engine seems to be sluggish throughout the rpm range; particularly next time I drive (like it has memory). If I drive more aggressively, which I have when I traveled (75+MPH) and opened the throttle more when passing, then it felt smoother and faster the next couple of days.

It's counterintuitive, but maybe the trick is to push it so the ECM programs itself to provide the necessary performance.

 

exactly!!