Yj 4.2 lacks power - Jeep Wrangler Forum
Jeep Wrangler Forum

Go Back   Jeep Wrangler Forum > YJ Jeep Wrangler Forum > YJ General Discussion Forum

Join Wrangler Forum Today


Reply
 
Thread Tools

Please support our sponsors and let them know you heard about them on WranglerForum.com
Old 07-06-2015, 11:14 PM
Thread Starter
  #1
Newb
 
Join Date: May 2015
Posts: 2
Yj 4.2 lacks power

I have a 87 yj with the 4.2 5 speed with 307 gears. My jeep has a hard time keeping up on the highway at 65 is this normal? First second and third pull ok but fourth and fifth are a dog big time.

jeeper greenhorn is offline   Quote
Old 07-06-2015, 11:31 PM   #2
Jeeper
 
Decoy_58's Avatar
 
Join Date: May 2013
Location: Central Calif
Posts: 594
What size tires
What size lift
I run 33s on my 90 had 307s could not use fifth
gear. Have now went to 410s massive
difference now i can use fifth and gain speed
one of the best things i have did LUV IT

__________________
1990 4.2 MPFI, 1" body lift, 1" shackle lift
,2.5 suspension lift, 9500lbs winch,33x12.50x15
tuffy glove box vault,smittybilt locking consol,
4:10 gears,new steering column,S.S brake lines,
new sound bar,new head unit,new roll bar pads
HANG THE BASTARD ECV (DECOY)58
Decoy_58 is offline   Quote
Old 07-06-2015, 11:32 PM   #3
Supporting Member

WF Supporting Member
 
Tom95YJ's Avatar
 
Join Date: Sep 2013
Location: SLC, Utah
Posts: 2,831
Quote:
Originally Posted by jeeper greenhorn View Post
I have a 87 yj with the 4.2 5 speed with 307 gears. My jeep has a hard time keeping up on the highway at 65 is this normal? First second and third pull ok but fourth and fifth are a dog big time.

What size tires are you running ?

Do you still next a stock carb or distributor ?

I'm running 3.07's and 35's until the spring then I will have 4.56's and my built 8.8 installed but I have no issue maintaining 65-70 in 4th gear on the hiway. I also have a weber 38/38 carb, and hei distributor , and 2.5" hiflow cat and cat back. Which really woke up the 258
__________________
1989 YJ : Lifted/ Armored Tom95YJ's The Smurf Build Thread
1999 XJ : Lifted/Locked/Armored
Tom95YJ is offline   Quote
Sponsored Links
Advertisement
 
Old 07-06-2015, 11:41 PM   #4
Supporting Member

5-Year WF Supporting Member
 
CyndiB's Avatar
 
Join Date: Jul 2011
Location: Inland Empire, CA
Posts: 1,536
You might want to check your cat. I have a 90 4.2 with the stock Carter carb, 4" lift and 33" tires and have no problem doing 70-75 on the freeway. But I never use 5th gear unless I'm on a flat stretch of highway. It does bog down a bit on the hills but I can still keep up with the cars in the middle lane.
CyndiB is offline   Quote
Old 07-07-2015, 12:45 AM   #5
Jeeper
 
Nubby55's Avatar
 
Join Date: Aug 2011
Location: north of St.Franisville La.
Posts: 3,834
Send a message via Yahoo to Nubby55
I'm only on 29" tires and stock every thing just Nuttered ,but my old Heep will run way faster than you have Guts to drive it, over 80 you get Real Busy! It's Short!
__________________
The Government can not give anything to anybody that it does not first take from someone else!
90 YJ,4.2 A/T,A/C,P/S,P/B, 3.07,235/75/15"Nutter, Carter non stepper,2.5"lift and Booms
Nubby55 is offline   Quote
Old 07-07-2015, 01:19 PM
Thread Starter
  #6
Newb
 
Join Date: May 2015
Posts: 2
I am running 31s on stock steel wheels with a 4in lift. I have new exhaust and a new weber carb.
jeeper greenhorn is offline   Quote
Old 07-07-2015, 02:30 PM   #7
Supporting Member

WF Supporting Member
 
Tom95YJ's Avatar
 
Join Date: Sep 2013
Location: SLC, Utah
Posts: 2,831
Quote:
Originally Posted by jeeper greenhorn View Post
I am running 31s on stock steel wheels with a 4in lift. I have new exhaust and a new weber carb.
I suggest looking into a CRT performance hei distributor and making sure your carb is properly jetted . Look into plugs and wires too along with a fuel filter
__________________
1989 YJ : Lifted/ Armored Tom95YJ's The Smurf Build Thread
1999 XJ : Lifted/Locked/Armored
Tom95YJ is offline   Quote
Old 07-07-2015, 03:31 PM   #8
Jeeper
 
Nubby55's Avatar
 
Join Date: Aug 2011
Location: north of St.Franisville La.
Posts: 3,834
Send a message via Yahoo to Nubby55
Check your timing, mine is set at 12deg. BTC, when I had it at 8deg. as some one said to start with it ran good but low power then I went to 10deg. and better, the last year or so at 12deg. and runs great and better MPG, about 14 MPG and I don't baby it.
not all engines are the same, wear on different parts make them all run better at different timing. good luck, play with it back and forth.

__________________
The Government can not give anything to anybody that it does not first take from someone else!
90 YJ,4.2 A/T,A/C,P/S,P/B, 3.07,235/75/15"Nutter, Carter non stepper,2.5"lift and Booms
Nubby55 is offline   Quote
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off






All times are GMT -5. The time now is 09:59 AM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.1
User Alert System provided by Advanced User Tagging v3.1.0 (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.

Jeep®, Wrangler, Liberty, Wagoneer, Cherokee, Gladiator, Mopar and Grand Cherokee are copyrighted and trademarked to FCA US LLC.
Wranglerforum.com is not in any way associated with FCA US LLC.