Hey guys I am finally back. I went and bought a 2000 Grand Cherokee and need some advice. I noticed while riding down the highway if I tried to accelerate the Jeep struggled and had an odd vibration. The engine was just rebuilt and the only miles it has are the ones I have been putting on it (125 miles so far). The GC has a 4.0 with an automatic transmission and its only 2 wheel drive. Any and all help would be great.

 

Two things I can suggest, check the torque converter bolts and bell housing bolts for being tight. Also the rear u-joint bolts and the trans mount. Make sure the u-joint caps are fully seated.

Loose bell housing bolts can tear the center out of the flex plate.

 

Thanks for the quick reply. I will check those asap. Do you happen to know the torque specs for the bolts?

 

No, but I'd say as tight as you can get them with two hands and a 3/8 ratchet. You might want to use some light duty Loc-tite.

 

Will do thanks.

 

Finally got around to checking the torque converter everything is tight and this seems to have fixed the vibrations. How do these beast compare to the XJ performance wise? Seems like for a new 4.0 its a bit underpowered compared to my old XJ on 37s and stock gears. Even when I floor it itll rocket thru the rpms but doesnt really go anywhere. Any advice as to what might be the cause?

 

The Chrysler transmission has more parasitic loss than the more efficient AW4 in the XJ, plus a WJ is quite a bit heavier than an XJ.

 

Yes, my WJ's unladen weight is 3980 lbs. I believe your XJ is much lighter and probably has lower gears. My WJ has 3.55. My '97 ZJ 4.0 felt like a rocket at WOT with 3.73's.

 

Dang Iv got to figure out how to increase my power with out breaking the bank lol. I like the Jeep but its slow

 

My "04" isn't a 4.0 but a 4.7HO and came stock with the towing package and 3.73 gears. It runs extremely well and fast for what it is with over 200,000 mi. on it. If your 4.0 is an complete rebuild with only 125 mi. on it the rings aren't even broken yet or any of it yet. This could account for some power loss, are you getting any codes or are they all good and sensors working.


Was the head rebuilt/replaced as well and what about the injectors?

 

Head and injectors were replaced. Iv got 4000 miles on the motor now. My Fiance drives all over God's green earth lol. The WJ did come with the tow package and trailer break controller. Not sure of the gears yet will check on that.

 

Ya Know? I'm sick and tired of people telling me the 4.0 is a slug. It's a reliable "tractor" engine, designed for torque, not gut wrenching acceleration. It's quick enough to get me out of a couple of on-ramp near misses and that's all that matters to me. I've had a couple of super-cars that needed constant tweaking to stay quick, but I'm over that now. I'd rather have a car that starts every time and does what I ask in normal service than a high-strung power machine. Yes, I've been there, but that's water under the bridge at this point in my life.

Call me an old fart if you like, it's true, I am an old fart.

 

Ya I know its a "tractor" engine. Was comparing it to my old XJ on 35s. Just seems like the WJ is slower. Even at 70 I have to floor it to get it to pass on the interstate. Where as my XJ even with stock gears I could use less throttle and rpms to get around people at the same speeds.

 

Slim, I don't know the HP & torque figures of the top of my head, but I recall reading about the "hot-rodding" mod of putting a 99+ intake on a 98- head (maybe only certain years like 95-98) and it claimed that the mixed engine produces more power than either of them did originally. It said that the 99+ were redesigned for better emissions, and in order to continue to produce acceptable power, the intake was fine-tuned. However, the head would considerably flow less than the 98-, resulting in a total package that was either slightly worse or only slightly better than previous. I think they say 93-95 heads flow the best. So whatever you had before would feel different, because even if the HP & torque max values are nearly the same, the power band and throttle response will be different, giving a very different seat of the pants feel.

 

Yeah, I did notice the earlier 4.0s made max torque at 3000 rpm where my WJ's figures are 4000 rpm. So, having said that, the mid-range torque is less compared to the '98 and older. At 65 mph, it's around 3000 when it kicks down to 3rd gear for passing. Also, I've noticed the transmission seems to lag making up it's mind what gear to downshift to. Several times, I've been trying to merge on an on-ramp and it won't immediately downshift so I boot it some more, only to have it downshift to 2nd!