trans " hunting" and bad mpg's
 

I have a 09 JKU with a 2 inch Rancho lift, 315-70-17 bfg A/T's, banks ram air, superchip programer, stock bumpers, 3.73 gears and a few other goodies. I have 125k on her.

Basically i fell like the trans is always hunting for the right gear, unless i am driving 80+ but it is a jeep that's about as safe as running with scissors. I was hoping my superchip would have corrected this that's why i dropped the money on it( have tried it all the different tunes.) After i am at speed it shifts at least 2 times every 30 seconds correcting and over correcting itself ( at 30, 45, 60 pretty much any speed.) My guess is this is why i a getting only 12.5 in the city on a good day and about 13-15 highway unless the wind is pushing me down the road. I am almost worried my trans is going to blow because of the non stop shifting :sad2: . I am not going to re-gear i have drove in jeeps with 6 inches of lift 37s and stock 3.21s with out this problem even though i know it would help, but i would rather save for a super charger then dump money in to a d30. The only thing i could think of is and its a far shot with the rancho lift the front is perfectly level if not a little taller then the rear because of new 2 inch coils up front and only a .75 inch spacer in the rear. Could changing the factory rake affect the wind resistance that much ? I am lost any help would be great thanks all in advance! :thumbsup:

You reprogrammed the tire size with the superchip, right?

Too bad a regear is not an option for you. It's likely the only thing that will help. You need to get the engine rpm's back up.

Just turn over drive off. I'm with you on throwing money on Dana 30, the pinion is just too small. Once your rpms reach 3000 and you want to go faster, turn OD on. Pain in the yes. But much cheaper than a new axel, gears, Hemi.

Are you sure it's not an overdrive issue?

I would incourage you to look more into the regearing. A D30 upgraded and taken care of will run 35s for as long as you own the jeep. You can add all the bolt-ons you want, but it's still going to be a slug with 3.73.

Yes i did reprogram for my tire size its almost dead nuts on. When i do turn overdrive off it keeps my rpm's up on the highways and that helps, and i have accepted i will never go over 60 mph( with o/d off high rpms) again but it dose not help for my city driving. I am fine with how it accelerates i just wish there was a better tune that would correct this sorry excuse of a auto trans. This was my first and last auto in years lol.

Well, you are right about the transmission, but it's the combination of it and the 3.8 that makes it bad for bigger tires.

Mine is fine with stock tires and 4.10 gears, (but just barely fine). I keep O/D off around town, and on all non-interstate 55 mph roads.

about time someone is with me on the d 30 lol i just need to find a wrecked rubi or something i would not mind just changing out the gears on the rear. But by the time i buy a new axel beef it up new gears in the rear its going to be around 3k. This experience makes me miss my f150 on 40s my millage hardly changed and it drove the same as when i got it.

I am one of the few people who defend the 3.8 just because i know its a tough well tested motor. They will last 300k + if taken care of. That being said i know they are a dog and people with motorized wheelchairs will beat us in the 1/4 mile.

Anyways what tune should i be running ? I am using the 93 performance right now because i fell it is giving me the best mpg's oddly enough.

Ahh, but I'm sure when the doors and roof are off you have a huge grin on your face. I know I do.

You got me there but with 10 inches of snow on the way that dream of the top being off again is the only thing keeping the keys in my pocket!

So i am the only on that thinks changing the rake will help a little bit ? lol