can't get above 50 mph! help!

[benlever]

Hi everyone! hope someone may be able to help me out with this before i involve a mechanic. Just got a '91 wrangler with lift, suspension, and 32in mud tires. It's only a 4 cylinder engine as well. Problem is i have great acceleration untill i'm going about 40 mph or over. 5th gear doesn't really do much of anything. Have a really hard time accelerating up hills in 4th and 5th gears. 3rd and below are fine. Jeep runs great and is well maintained too. Any thoughts would be great! even on level road i can barely hit 50 mph! is the engine just not powerful enough to move those big freakin tires or what? Shoulda just gone back to a CJ... lol
Thanks for any help! -Ben

 

[TwistedCU]

I had a '92 with the 2.5L and 32's. After a good tune up, changing every fluid, and some cheap performance mods like a K&N "drop-in" filter, removed airflow restrictor, electric fan conversion (okay that one cost about $200 or so), gutted catalytic converter, dual tip spark plugs) it did better. Admittedly it was no powerhouse, but my YJ saw 75+ mph often with stock gears and 32's. It pulled up hills in 4th. I drove it daily to work and hit the trails often and was quite happy with it. I was pretty sure that the 32's were the limit for that setup though. If your motor is healthy (good compression, well tuned, and clean fluids/oils) then a few of these mods will help.

BUT

If you truly want to get it running strong, you should re-gear it. 4.88 Gears would put close to stock performance, heck maybe even better with only 32" tires.

 

[mingez]

You probably need to regear. Have you done so? I have never messed with a 4 cylinder Jeep, so I can't really comment on it's power, and whether or not it's powerful enough to push 32" tires to highway speeds.

Bounty Hunter has a 4 banger wrangler, and TwistedCopper used to have a one as well. Perhaps they can comment.

 

[mingez]

You probably need to regear. Have you done so? I have never messed with a 4 cylinder Jeep, so I can't really comment on it's power, and whether or not it's powerful enough to push 32" tires to highway speeds.

Bounty Hunter has a 4 banger wrangler, and TwistedCopper used to have a one as well. Perhaps they can comment.

Okay, Twisted Copper is too fast, and commented while I was composing my post.

 

[KrazyJeeper]

I have a 4 banger with 33's and mostly my problem is the wind. I can get up to about 60 in fourth but that's with the pedal on the floor. Going up hills in 5th doesn't happen. I looked into the throttle body and a few other mods, but when I was ready to buy, they were on backorder. Since I bought an XJ and when I know I have to be somewhere in hurry, I take the XJ. I still want to mod the TJ, but don't have much money right now. I have been told regearing would cost me around 1,000. Not mechanically inclined here.

 

[mingez]

Yeah, unless you have the "Hook up" it's gonna run you 800 to 1200 bucks.

 

[happy024]

I've got a 95 2.5 with 31s. Daily driver on Highway. I have only removed the intake restictores and I have no problem doing 65 or 70. But when the wind is kicking up or going up and steep hill I do need to go to 4th gear to keep up.

 

[KrazyJeeper]

Seem like I remember someone stating here that the TJ does not have the intake restrictor. Someone call me a liar please. If that would solve the problem, great. Thanks, KJ

 

[Sparky-Watts]

I've got a 95 2.5 with 31s. Daily driver on Highway. I have only removed the intake restictores and I have no problem doing 65 or 70. But when the wind is kicking up or going up and steep hill I do need to go to 4th gear to keep up.

Ditto. Flatlander here, so I can use 5th gear almost all the time at 70-75 mph, unless that notorious Kansas southwind is kicking it, then it's 4th gear and backroads at 55-60.

 

[Sparky-Watts]

Seem like I remember someone stating here that the TJ does not have the intake restrictor. Someone call me a liar please. If that would solve the problem, great. Thanks, KJ

Nope, yer not a liar....different intake, no restrictor......

 

[H2oSki2Live]

Sparky... any certain brand of spark plugs that you would recommend buying?

 

[TwistedCU]

Bosch's platinum with the dual tips are good. Splitfire isn't bad either. I like the dual contact plugs (obviously).

 

[Sparky-Watts]

Sparky... any certain brand of spark plugs that you would recommend buying?

I'm currently running Bosch Platinum with the dual tips, seemed to improve acceleration a bit as well as MPG. I've used Bosch pretty much in all my vehicles and can say they are very good, very dependable.

 

[H2oSki2Live]

Think I'll stop by the auto store this weekend

 

[Sparky-Watts]

Update: I checked this morning and found the old boxes from the plugs I put in, and they are Bosch Platinum Plus 4's........don't ask why I still have the boxes a year after I installed the plugs.....

 

[jpfvr]

I have a 95 wrangler with the 4 banger. Lift kit and 31x10.50 tires and 5th gear is a joke in mine. Like you said 1,2,3 all do pretty good but 4th lacks power and 5th I don't use because my speed drops when I put it in 5th. I have taken the restrictor out of the air filter box and that did help some. But you can't expect much out of this little engine. Like the others have said regear is about the only option if you want to get back to stock performance. My jeep will top out about 75 MPH on the interstate, that's fast enough for me. It sounds like you may need new plugs like the others have said. I also need to install them plugs in mine for that little extra power. I will regear later on down the road but for now I'm happy. Also remember your speed odometer may be off a little also. Mine is 3 or 4 MPH off. when I'm running 55 by the odometer I'm really running about about 58 or 59. Good luck with it all 8)