it is a combination of things including speed/rpm load etc. I was told by the person who invented the procal it adjusted shift points to where Chrysler intended them to be. AEV started a couple miles from me. The R&D shop is still local in Missoula, Mt.

 

The OP's question was will reprogramming get back some of the lost mpg. The answer is reprogramming will make his mpg calculations more accurate. He will recover some of the "lost" mpg.

 

That's good information. I have never read that before. Thanks.

My thought as well. It will help with the numbers but not actually change the gas mileage. But if it improves shift points then it actually can increase mileage I would think.

 

If his auto is bogging in too high a gear, it would help, but don't expect I huge gain.

 

I honestly wouldnt reprogram it unless you want the MPG and the odometer to display correctly. I noticed when i went from the stock 16" steelies to the 17" alloys that my odometer would read less miles than was actually driven. I was pretty pumped about it because the odometer showed less miles than was actually on the jeep. But my MPG indicator was off by a little which I dont really follow anyways.

 

Thanks for the replies.

I don't care so much about MPGs, just wondered if that would be affected.

The real issue is not speedo either, I don't care if its off.

My concern was in how the computer managed the engine and trans. Does a heavier tire cause the computer to think the engine is running harder than it should and does the computer compensate somehow, ie shift later, change fuel mixture, etc. The dealership led me to believe that to be the case.

Or, does the computer NOT compensate, and does reprogramming accomplish anything along those lines?

If all reprogramming does is adjust the speedo, I don't care to reprogram.

I only really pointed out the MPGs on the off chance that would be affected, and also to show how much performance was impacted I case it was out of line with what others have seen.

It seems to be running well, with the only difference being that it seems to downshift in to fourth more often than before while keeping the cruise control at 70 on the highway.

 

Not sure why anybody would not want there shift points to be optimum, I guess to each is own. I have had to reprogram two wranglers 13 and 14 and seat of the pants notice a shifting difference. Might be placebo but makes me happy.

 

I ordered a set of 17" rims and 33s yesterday. Going from the 18" rims I already have. The guy at the off road shop told me that he would not reprogram because it will only be a few MPH off. I asked him about the shift points and stuff like that and he said it will not matter. If I will in fact need to change the shift points then condsider a programer bought, I don't want to half ass this stuff. I'm to old and have half assed to much stuff in my past to do it these days lol

 

With 33s you really don't need to. I ran like that for most of a year. When I finally did, mainly to turn off the TPMS light, I really didn't notice a change in shifting.

 

If you get the Superchips Flashpaq tuner, you can recalibrate your speedo, turn off your tpms light (if you so desire), correct shift points, and do a 87, 91 or 93 octane tune which WILL increase your MPG as well as increase power and torq...along with other things. Well worth the $$.