4.2 to 4.0 swap

My 1990 YJ when it still had the 4.2

When i got my yj wrangler a couple of years ago, i noticed it had a carbureted motor in it and I didn't really think much of it because I thought it would be a good motor since it was a six cylinder.  After driving it a while, i realized I was wrong.  It leaked and burned a lot of oil, about 1-2 quarts per week.  It also wasn't very powerful, and it had bad gas mileage, which was around 10 mpg.  After driving it for about a year with that motor, i decided i should try to find a motor to swap into my jeep.  At first,  I wanted to just try to put a head from a 4.0 on my motor which would give it about 30-50 more horsepower, but i wanted to go with fuel injection.  Then, I wanted to put a 5.3 Liter V8 out of a 1999-up chevy truck, but after some shopping, i realized that would be over 1500 dollars, plus having to deal with the axles breaking over time and having to change the motor and transmission mounts.

After doing a bunch of research online, i realized a 4.0 out of a cherokee or a newer (91-95) wrangler would bolt right in and would need minor wiring modification.  So, i tried to find a cherokee motor, but it was hard to find one that wasnt parted out already.  Since i was going from carburetor from fuel injection, i would need the fuel lines and gas tank from the donor vehicle.  After doing some searching, i found out that a junkyard near where I live had just gotten a 1994 wrangler with a 4.0 and a manual transmission, which is really nice because if I were to get one that was bolted up to an auto, i would have to get a new computer for the manual transmission.  So, i decided to get the one from the wrangler.

In future posts on this blog, i am going to describe the steps i had to go through to get the new 4.0 liter motor to work in my wrangler with the 4.2.

Doing the Swap

     After getting the motor from the donor (the 1994 wrangler with the 4.0 liter motor), i started to disconnect the coolant and radiator hoses and removed the radiator.  i also took the washer and coolant bottles out aswell as disconnected the power steering hoses.  Then i disconnected the 4.2 wiring harness from my jeep.  I decided to keep the harness connected to the motor so it would be all one piece.

     After everything was unplugged, i unbolted the motor from the bellhousing, unbolted the motor mounts, and took the motor out.  The 4.0 motor bolts right up to the motor mounts that the 4.2 used, so there is no cutting and welding required.  I decided to keep the internal slave cylinder because the clutch master cylinder did not bolt up to the firewall.  The 4.2 bellhousing also has the hole for the crank position sensor, so you can use the original bellhousing.  It was very easy to put the 4.0 motor in.  The power steering reservoir on the 4.0 motor just bolts up to the flange on the radiator.  There is one hole already there but you can drill another if you want to.

     In the next post i will talk about wiring up the motor.

Wiring

For the wiring part, I could not find any kind of write-up for swapping a wrangler 4.0 into a wrangler that had a 4.2.  All of the ones i found used cherokee 4.0 motors.  So, after i put the motor together, i realized that nothing but the lights would turn on and i figured it would be a hassle to figure out the wiring.  Then, i found a website that helped me out a lot, since i could not find anything by searching.  Its www.alldatadiy.com and it gives you everything you need for wiring diagrams.  You have to pay a little bit for it, and you can only look at one year of one certain model vehicle, but it lasts a year and it is worth it in my opinion.

     There is a body harness connector that goes through the firewall next to the steering column, to the left of it if you are looking under the hood.  You are going to need that plug.  You will have to cut it off of the donor vehicle so you can wire up the gauges, the starter, and the radio.

     Here are the wires you need out of this plug:

     Red-Constant power for radio/cd player (or anything you want to have constant power)

     For gauges:
     Purple and Yellow-Engine Coolant Tempurature
     Grey and Yellow-Engine Oil Pressure
     Dark Blue-Fuel Level
     Yellow-Starter

     These are the colors of those wires at the old gauge cluster:
     Purple-Engine Coolant Temperature
     Light Blue-Engine Oil Pressure
     Tan-Fuel Level
 
     What I did to connect the sending unit wires to the gauge wires was i used wire to go from the gauge cluster to the connector.  I just cut them at the gauge cluster one at a time and ran them under the dash.


     The yellow starter wire will splice into a dark green wire that is in the connecter that is on the upper side of the steering column, under the dash.

     Also, for the fuse box that is for the 4.0 motor, i just mounted it onto the side of the original battery mount instead of putting the newer style one in there, which puts the battery parallel with the firewall and the fuse box in front of the battery.

 

      After doing this, i was able to start up my Jeep and drive it with the new motor.  It was a lot easier than i had expected.  If you use a Cherokee motor, you have to tear apart the bulkhead connector which is to the right of the brake booster because a few of the wires are in different spots on the Cherokee.