KenSmithMT

Hey, You all provide a lot of great info. Thanks! This is my first post. I’ve searched many threads but seem to find the same stuff. Close but not quite what I’m asking.

I have a lack of power I'm trying to figure out. I have a 2010 JKU with the stock 3.8L and automatic transmission. The factory setup was 29" tires and 3.73's. When I bought it the tires were trashed so I did not drive much on the highway. I bought 32's and immediately noticed I could not maintain speed on the highway with headwinds and hills. I changed to 4.56 gears and added a Banks Ram Air intake. Much better but I still have a hard time keeping speed with hills and headwinds. I have two sets of wheels and tires. 32's and 33's. The motor has 185,000 miles but is tight. Compression is good in all 6. It just seems like I should be able to hold speed better. Any thoughts? I've ran this by several local shops but they are not Jeep experts so don’t have a good basis for how much power I should have. It seems to run great otherwise.

Thanks

rob_engineer

I'm sure you've done this already, but please confirm you reprogrammed for the gears and tire change.

jchappies

Welcome to the 3.8L Auto hunt for power club.
1: re-gear for more low end power (4.88)
2: Add a superchips or programmer for tuning
3: add a power adder like RIPP supercharger
4: sell it for a newer model (2012+)
5: Go big, V8 Hemi or LS motor swap

Riptide9

+10000000

1: Regeared - little help
2: bullydog programmer - no help
3: added Sprintex Stage 2 supercharger - made it drivable but still sucked
4: Almost thought a about selling it (my wife has a 13 Rubicon w the 3.6 and it made me jealous)
5: Said screw it and went big - dropped in a 6.0l LS with the 6l80 6 speed trans from RPMExtreme - HOLY SH!T ! WOW Thats the way it is supposed to be (chirps my 40's on dry pavement on every shift we you get on it)

KenSmithMT

Thanks Rob

Yep - Used a FlashPaq to tune, set wheel size and gear ratio.

jtphoto JK

Go back in there and look for the Speedo limiter and bump that all the way. That limiter starts backing the fuel and power off as you increase speed. It set by the factory at 100mph but it starts cutting in well before that.

VEGASROBBI

Power to pass? Try a new GM LT 6.2 8 speed, it will pass while smoking the 33's lol; a powerful engine.

Seriously 180k miles is a lot of miles on a 3.8. While compression may be balanced I would check vacuum at idle, what is the cranking compression? Worn cylinders, slipped or stretched timing chain, carbon build up, stuck egr valve...can all be causes of poor performance.

Since an IC engine is essentially an air pump first thing to check is it pumps the appropriate air. There are other causes like plugged exhaust, low fuel pressure... you'd be surprised how much a vacuum gauge can reveal if you know what to look for.

Mike H.

are you still running the original catalytic convertors?
if so, my first guess is that those are dang near plugged up... then, as mentioned, all the "little" tune up type items.

jadmt

something is wrong, with 4.56's and 33's you should be able to maintain speed all day long. sure wont be a power house but should not have problems driving 70. Hit one of the local indy shops and see if they can put it on the scope to see what the issue is. Adams auto comes to mind as Floyd Adams has always struck me as honest. I have heard good things about the place on west broadway by that self serve car wash as well. Might stop in and talk to Jeremy at J&K he has a 3.8 in his jku.

jadmt

x2...........