I still own a 03 TJ 4.0 4.56 33's, & many many accessories etc...., and have owned a few other TJ 4.0's not to mention have drove many Cherokee's, and Grand Cherokees (used to sell for Jeep). Last night was my 1st experience driving an 09 JK 2dr X 6 sp. (don't know the gears), it had 32" aftermaket tires and wheels, and that was it. Completely plain x other than that. And i have to say i don't understand where the complaints about HP are coming from? This little 09 2dr X model had more "get up and go power" than any other Jeep i've been in short of V8 conversions. It could easly smoke any 4.0 i've driven from 0-60 and point A to B, Is it the offroad low end that everybody is talking about or what. I offroad a bit and don't get me wrong i luv the 4.0 off road, but i don't think it can ever compare to this new 3.8 on the highway. Please post any opinion you have about this, i guess i'm just not understanding what the complaints are. thx.

 

My only complaints about the engines lack of power is in the mountains, or in a headwind. I know that I drive a brick, but at the same time in a headwind (even a slight one) I need to turn the OD off to maintain a speed, otherwise with the cruise on it will slowly lose speed, or maintain about 5 under where I want it to be, and then downshift to third making the tranny work harder too.

In the mountains on the highway where I go the speed limit is 75, and in our Liberty, or our Grand Cherokee we could maintain the speed going up the mountains, and accelerate if needed. On the JK it would lose speed in third gear, and be bouncing off the rev limiter in second and this is going about 55-60, so about 15 under the speed limit. Sometimes for safety I want the power to get around something that I view to be a hazard. A good example about this is there was a tow truck cleaning up an accident on the pass on my way back from Montana at about 4:00 in the morning. I could tell that he didn't have the load secured properly, so I would normally just power around him. In the JK when I tried doing this I ended up next to him when the bumper flew off into my lane.

The third thing is that after driving the JK with a 5.7 Hemi it is amazing the difference in the engines. You never have to plan ahead with passing anyone on a 2 lane road since you know you always will have the power. You will consistintley get better gas mileage. I also prefer to maintain about 5 over the speed limit when I am on the highway, and the Hemi can maintain it using the cruise. With the JK it maintains about 3 under (unless I would drive in third the whole way). I regularly go to Western Montana and in the JK it takes us about 2.5 hours extra to get out there compared to when we have taken our WJ, or KJ, which is a lot when you could be in the car 17.5 hours, or 20.

 

you got it, its the low end power. i myself am an automotive tech and have driven many different jeeps with the 4.0 and when i first drove an x it was and still is better on the street and highway. off road is a different story, if you've got it wound up around 4500rpm with all tires spinning going up a good climb(sand, mud, deep wet snow) and the engine starts to work hard the rpms will slowly drop off, and when the rpm's hit around 2500 it just falls flat on its face and the rpm's drop to nothing and it stalls. it is a little better in 4lo but having to stop to into and out of 4lo is a pain in the ass. the 4.0 may not make the climb either but the rpms will never fall off and stall like a jk. i'm going to try better gears a have 4.10's now and i would say that is the lowest you would want to go

 

Also one big thing that i noticed is that you have to drive them different. I also own a 99 4runner w/ a 5sp, and it seems that you have to drive the JK's like it. Instead of the TJ that you shift between 2700 & 3000, you can rap these JK's up to 4500 rpm and it seems to have plenty of power when you get them there. Once you get a TJ to 3000-3500 they are done.

 

hmm thanks for the comparison ... i find many jk owners, including myself, are used to driving high performance cars and find the power plant the engineers chose for the box of a aerodynamic wonder to be lacking based on those previous experiences ...

longer i own it the more i get used to it ... and with 17k on it, it either loosened up alot or i got used to the power cause i have no issue with it refusing to do 65 in over drive on a slight incline.

 

I too owned a TJ and I recall it feeling "peppy" on the low end and gasping for air on the high end on the road when it was stock. Off road the power was good to adequate the vast majority of the time (again stock).

In between, I unfortunately strayed and owned an FJ whose main strong point was the 4.0L engine. I expect that Chrysler with the Dodge under its corporate umbrella design an engine that is least comparable to the Toyota powerplant. After all this is a 4000+ lb rig not a 3000 lb minivan.

My JK which I would not trade regardless feels like I am stuck in 4-Hi. IMO, the usable power band is between 2200-3500 rpm which is high and limited. I will soon be driving in that range thanks to a set of 5.13s.

I am just very disappointed that Jeep blew the opportunity to put in a real engine out of the MOPAR arsenal when replacing the venerable 4.0L. I know that CAFE ratings have a huge impact on auto product lines, specially when you are going bankrupt, but we are taking about JEEP here!

 

I think that a lot of people forget about the weight of the JK. Once you add on bumpers, skids, larger tires, etc... you can easilly hit 5,000lbs. Add in a week of camping gear, a few people, etc... and you are into the 6,000lbs range. This is in the range of a 3/4 ton truck, and those come with a V8 minimum.

 

You are correct sir. I drive regularly between 6,000 and 12,000 feet in the mountains with no issue. Complaints about the lack of power (especially from those at or near sea level) is grossly over-stated.