1990 Cherokee Slow Acceleration. - JeepForum.com
 
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post #1 of 5 Old 09-20-2016, 09:55 PM Thread Starter
FrazierMedina
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1990 Cherokee Slow Acceleration.

I have a 1990 Jeep Cherokee Renix 5 speed, ax-15 4.5" long arm and 33's. it’s the base model and everything in the engine is stock, some new parts but no upgrades. Ever since I got the Jeep stock a little over a year ago, it’s had super slow acceleration. Taking me about 10 seconds to reach 60 MPH using .4 miles of road. I’ve always assumed it was because it’s a 26-year-old Jeep. After looking at videos of 88-90 Jeeps accelerating fast, I was confused on how they are able to accelerate and have high rpm's no issue with both auto and manual. My tires have little to nothing to do with it since I have the same acceleration with 29's and 33's at same RPM. I've been having this issue before ever modifying my Jeep. With 29x9.5" tires 30x10.5" tires 31x10.5" tires and 33x12.5" tires, I've had the same exact acceleration at the same RPM's

I recently upgraded my cluster to one with a tach and no dummy lights. Here I noticed that the good shifting point is 2k rpm and it’s pretty loud at that (super 10 muffler) I don’t even want to take it to 3k RPM because of how much of a hard time it has getting there. 1: its uncomfortably loud (not an issue, just scary) 2: The Jeep feels like it’s going to explode. I watch acceleration videos on YouTube and see people at 4k rpm and no issue. In the videos their 5k RPM sounds like my 2k RPM.

Could there be an issue with anything not allowing me to accelerate fast or get to higher rpm's smoother?
Why do I have slow acceleration?
Am I just being a baby about it and not pushing it hard enough to get high rpm and fast acceleration?


Last edited by FrazierMedina; 09-21-2016 at 01:10 AM. Reason: Probably not clear enough that I've had this issue regardless of tire size.
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post #2 of 5 Old 09-21-2016, 12:52 AM
Timo_90xj
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With correct gearing your XJ with a 4.0 + manual tranny should accelerate 0-60 in under 10 seconds. Heck, even if it was automatic it should do it in under 10 seconds. IIRC my XJ 4.0 + AW4 on 35s and 4.88 gears took about 9 seconds.

Wide open throttle and taking your engine up to redline should not be an issue, as long as the engine is working. 4.0 does have a noisy valvetrain, but it's not going to explode at 5k RPMs.
Can you record a video of how your Jeep sounds, and a clip from the engine bay if you have any abnormal sounds on the engine?

1998 Grand Cherokee 5.9 LX daily driver, 1.75" BB, 32" KM2s, HPD30 Eaton e-locker/D44a stock LSD, 4.56 gears, custom- fabbed tube bumpers and tube fenders,...


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1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
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post #3 of 5 Old 09-21-2016, 01:04 AM Thread Starter
FrazierMedina
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Quote:
Originally Posted by Timo_90xj View Post
With correct gearing your XJ with a 4.0 + manual tranny should accelerate 0-60 in under 10 seconds. Heck, even if it was automatic it should do it in under 10 seconds. IIRC my XJ 4.0 + AW4 on 35s and 4.88 gears took about 9 seconds.

Wide open throttle and taking your engine up to redline should not be an issue, as long as the engine is working. 4.0 does have a noisy valvetrain, but it's not going to explode at 5k RPMs.
Can you record a video of how your Jeep sounds, and a clip from the engine bay if you have any abnormal sounds on the engine?
ill record a video tomorrow, there is no abnormal sounds from the engine bay, everything is healthy.
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post #4 of 5 Old 09-21-2016, 02:37 AM
Timo_90xj
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Btw., what is your axle gearing? I did notice you mentioned acceleration has been bad on stock size tires up to 33s, but the undeniable fact is if you have OEM gearing on the axles and go up to 33s, it WILL affect your acceleration.

If the acceleration was just as bad with OEM tires as it is with your 33s, then there sure is something wrong. However, 0-60mph in 10 seconds with 33s with a 4.0 + stick shift on 3.07 gears sounds about right. It won't do it any faster than that unless you swap in shorter axle gears.

1998 Grand Cherokee 5.9 LX daily driver, 1.75" BB, 32" KM2s, HPD30 Eaton e-locker/D44a stock LSD, 4.56 gears, custom- fabbed tube bumpers and tube fenders,...


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1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
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post #5 of 5 Old 09-23-2016, 07:46 AM
cruiser54
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As stated on another forum, aside from high gearing, you're lugging the engine badly.

If you own a Renix Jeep, you must check this out:


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My Jeep technical photos:


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