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Old 05-25-2012, 02:48 PM   #1
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I can't only hit 70 mph

I have a stock 94 yj with 4.0 ho. With the pedal to the floor in fifth gear all I can't get is 2600 rpm and around 70 mph. Is this normal for a jeep. By the way, this is my first jeep.

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Old 05-25-2012, 02:49 PM   #2
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Can only hit 70 mph

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Old 05-25-2012, 03:14 PM   #3
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No that's not normal. If everything is stock that's a bit slow for max speed. The only time my 89 YJ ran great otherwise but wouldn't get up to speed is when I had a clogged cat. Replaced it and everything back to normal. All things being equal, there might be some type of restriction.
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Old 05-25-2012, 03:14 PM   #4
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I would say so. I mean its almost 20 years old and may have some lag. What size tires do you have and what milage. I have the exact same set up. 115,000 on the odometer. Mine will go 90 in 5th at 2900 but its been looked after well and has factory tires
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Old 05-25-2012, 03:26 PM   #5
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I have 31 10.50 on stock rims. I will look in to the cat. I plan on doing a full tune up this weekend. Anyrhing else I should look out for. Already doing drive shaft u joint.
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Old 05-25-2012, 03:59 PM   #6
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I have a 94' YJ w/4.0 HO. 80mph with more to go last time on the expressway. Im running 33 12.5 15's with an automatic trans (3.73 gears)

check your air box, make sure its not full of leaves or something... I've seen engines choke out at 55mph or so because of this.

lift each wheel off the ground with a jack and spin it. Make sure there is no drag from the brakes.

put it N not running on flat ground, you should be able to push it (roll it) without any resistance.

or it could be running on 4-5 cylinders with a fouled spark plug...

hard to say without checking those other things first.
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Old 05-25-2012, 04:51 PM   #7
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70mph and 2600 rpm.... My buddies TJ is a 5 speed manual with the 4.0 HO, rolling on stock tires, yet at 75mph it's running 1900rpm. What kind of gearing do you have? You should be running less than 2000rpm with 31" tires in 5th gear.

Keep in mind 31" tires offsets the speedometer by about 11%, so at 70mph on the speedo you're really going 77mph. A cop will ticket you for that, don't tell him the speedometer is off, otherwise it will make things worse (failure to maintain proper vehicle operation, etc).
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Old 05-25-2012, 07:12 PM   #8
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Wow I need too get on the swap soon . In my 2.5 with stock tires and gears. 75 would be about 3000 rpm. I cruise at 65 at around 2400 rpm
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Old 05-25-2012, 09:50 PM   #9
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my 87 automatic does about 100 mph but i didn;t look at hte rpms and the wife's 93 automatic did 100 mph also so i think something is wrong with yours. automatics only have 3 speeds and hers was rolling on the stock 15s with some tiny tiny 205 tires
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Old 05-25-2012, 10:00 PM   #10
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Jeeps aren't meant for speed!
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Old 05-25-2012, 10:02 PM   #11
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mine is a sleeper.
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Old 05-25-2012, 10:51 PM   #12
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Speed

Zei,

My 89 W/258 I6 tops out at about 70 as well was told it may need a new carb, i will check the cat i imaging it is plugged solid, but as others said, its not going to break any land speed records, check your gearing abd let us know how it does after tune-up.
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Old 05-25-2012, 11:19 PM   #13
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My 5 speed manual 92 4.0 HO has hit 75 mph in 4th gear. Granted I was on a slight hill but hey it still hit it!
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Old 05-26-2012, 12:05 AM   #14
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Quote:
Originally Posted by busemans
my 87 automatic does about 100 mph but i didn;t look at hte rpms and the wife's 93 automatic did 100 mph also so i think something is wrong with yours. automatics only have 3 speeds and hers was rolling on the stock 15s with some tiny tiny 205 tires
There is nothing wrong with my jeep lol it runs great
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Old 05-26-2012, 07:49 AM   #15
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As stated needs looked at. I run a 95 4.0L auto 4.10's,33x12.50's, 65-70mph is running about 2700-2800 rpm as I recall.
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Old 05-26-2012, 08:03 AM   #16
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I pegged the speedo runnin 35's and factory 4.10s. Mostly stock 4.0 back then. When I first purchased my 94 in 95 it was all stock and had no problem pegging the speedo back then either.
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Old 05-26-2012, 09:01 AM   #17
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Just did the tune up. Is there a rev limiter in fifth gear on any jeeps. I can't get over 2 k rpm in fifth gear. Gonna try the cat next. Any help would be appreciated
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Old 05-26-2012, 09:13 AM   #18
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I have stock 3.07 s. The jeep will run 75-80 in fourth gear. When I shift back to fifth it drops to around 2000 rpm and holds at 70.
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Old 05-26-2012, 10:55 AM   #19
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Quote:
Originally Posted by Zei10280
Just did the tune up. Is there a rev limiter in fifth gear on any jeeps. I can't get over 2 k rpm in fifth gear. Gonna try the cat next. Any help would be appreciated
I can't get over 2400 rps in 5th with my 95 2.5 I'm also wondering if it may be the cat. I've also thought about doing the tb from a 4.0, would it b worth it to do the tb?
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Old 05-26-2012, 10:58 AM   #20
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Quote:
Originally Posted by busemans
mine is a sleeper.
I think mines asleep
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Old 05-27-2012, 11:16 AM   #21
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I can't get over 2400 rps in 5th with my 95 2.5 I'm also wondering if it may be the cat. I've also thought about doing the tb from a 4.0, would it b worth it to do the tb?
definitely check the cat, my jeep had issues getting over 65mph for a short time. Figured out it was the cat, also heard slight rattling noises from the cat when i started and stopped the jeep indicating some parts of the filter in the cat had come loose.
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Old 05-27-2012, 11:33 AM   #22
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Originally Posted by Zei10280 View Post
I have stock 3.07 s. The jeep will run 75-80 in fourth gear. When I shift back to fifth it drops to around 2000 rpm and holds at 70.
mine does the same thing
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Old 05-28-2012, 11:01 AM   #23
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bump
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Old 05-28-2012, 11:32 AM   #24
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If you have stock 3.07 gears, my advice to you is dont use 5th gear...lol. If you are going 75-80 in 4th, apparently you have never been in or witnessed a jeep crash.

That short wheel based vehicle isnt designed or meant to be going 80mph down the interstate or anywhere else for that matter. If you want to go fast, buy a vehicle meant for it, and thats not a jeep.

You have 31's which are about 3-4 inches taller than a stock tire, so your final ratio instead of being 3.07 is now down around the 2.60 mark. I know this cause my jeep had 3.07's with 33's and my final was at 2.42.

The engine and drivetrain isnt designed to run on that high of a gear and still pull you down the highway at 80. Sure you can re-gear for performance at any speed, but sit back and think about all the other factors involved. A 4wd was meant for slow speeds, highway driving at 55 and below.

You guys should get an old 1950's willys jeep with a flathead 4cyl, 3spd, and 5.38 rears. then you will know about slow. Mine will get to 40 on a good day with alot of downhill and a tail wind. But, it will climb the side of a mountain that would make a billy goat scared.
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Old 05-28-2012, 12:21 PM   #25
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Of your accelerating to a higher rpm in 4th then that would rule out the cat. As others have said you are geared to low for 5th gear to be usefull. You need to either regear your axles, put the stock size tires back on, or live with 5th gear being almost useless...
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Old 05-28-2012, 03:28 PM   #26
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You guys should get an old 1950's willys jeep with a flathead 4cyl, 3spd, and 5.38 rears. then you will know about slow. Mine will get to 40 on a good day with alot of downhill and a tail wind. But, it will climb the side of a mountain that would make a billy goat scared.

You're getting cheated, or old 49 CJ2A would do 46 pegged out.
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Old 05-28-2012, 04:07 PM   #27
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4x4s are not meant for 55 or slower. if they were then they would stop sellign them in the united states where all highway speeds are well above 55mph now. they are designed to drive on the highway, like any other vehicle. their primary design is travel on road and off-road happens to be an ability they can do also. their primary design though, is on road usage. i know its a jeep and the old jeeps were designed to not do more the 50mph but times have changed since them and jeeps are designed as normal vehicles, especially our yjs. early cjs fall into the catagory of being more off road but we all drive vehicles primarily designed to travel on the asphalt. if they were primarily designed for off-roading then you would not have sway bars or trac bars nor windshield wipers and flares.
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Old 05-28-2012, 06:32 PM   #28
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5th in a Jeep is a cruising gear not a speed gear. I can hit 70-80mph in 4th but when I up shift it drops to around 65-70mph. You are driving a vehicle that has the aerodynamics of a barn door.

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