by Scott Mackey

Here is my story on swapping a 93 Jeep YJ (Wrangler) 4.0L and TF999 automatic transmission into my 90 Jeep YJ that had a 2.5L with a 5-speed transmission. Enjoy!

First off let me preface this by saying that I strongly considered doing a V8 conversion but instead decided to do this. Here is my reasoning. The V8 I would have done would have either been a 5.0 or a 350, and I was leaning towards 5.0 because I know more about them and really like the engine. Here are the specs on the 5.0 I probably would have used, this is from a 94 Mustang:

215 hp @ 4200 rpm
285 lb-ft @ 3400 rpm

And here is a stock 4.0 liter out of a 93 Wrangler:

190 hp @ 4600-4750 rpm
225 lb-ft @ 3000-3950 rpm

Now, the main reason I didn't do the V8 was cost. I am just a lowly college student and I have loads of time and no money. If I had done the 5.0 it would have cost at least USD$3500 by the time it was all said and done with a wiring harness, transmission, engine, computer, radiator, shifter etc. After the mods I did (electric fan, intake, exhaust) the 4.0 is almost as good as the 5.0.

Instead I bought a totaled 93 YJ 4.0 with 87K miles on it for USD$1500. I used the entire drive train, gas tank, dash, roll bar, and a few other random parts. Sold all the rest, and my old parts and ended up making about $USD500 on swapping a 4.0 drive train into my Jeep. That was even after I paid for a new radiator, electric fan, intake, drive shaft shortening/lengthening, Tuffy center console and a few other random parts. If anyone is interested email me at scott@phillipsonline.com and I can show you what I bought/sold and the prices and stuff.

Now onto the swap: I started off by pulling the entire drive train out of my Jeep. We took the transfer case off and pulled the engine/transmission as a unit. That went pretty smoothly; pulling an engine is the easy part.

Dad and I...and yes, the huge shackles are now gone!

We then drove the donor into the garage and proceeded to do the same with that, but this time we were very careful in making notes about which wires/hoses went where, and labeled lots of them with orange duct tape. We took lots of digital pictures of the engine in the donor just for reference.

Next, a friend came over and we cut the motor mounts out of both Jeeps, making sure not to damage the frame in mine. We actually set the engine in the compartment with the tranny attached to the tranny skid plate to line up the motor mounts. On the advice of some people on the JU message board, we moved the entire drive train as far forward as possible as to get less of an angle on the rear drive shaft. This caused some problems and I will go over these later. We then tack welded the mounts in and pulled the engine back out so he could weld the mounts on completely. Then I painted the welds and put the engine back in. We used 1" motor mount lifts from MORE because the original mounts were shot. So far so good.

Then I pulled the dash out of both the donor and my Jeep. Everything matched right up and so it was not nearly as hard as I had imagined it being. So I now have a 93 dash in my 90, I also bought red lights so it glows red at night (woohoo).

Mounting the fuse box: Now the battery pan is different on the 4.0 than the 2.5 and it also has a big fuse box mounted to it. Instead of using the 93 battery pan, I just chopped the fuse box holder off of it and bolted it to the bottom of my battery pan. It only took about 20 minutes.

Mounting the Computer: On the 2.5 for some reason the computer is on the inside underneath the dash and it is in the engine compartment on the 4.0. So I simply drilled 3 holes for the CPU, got some lock nuts and long bolts and bolted it it. Very easy and simple. I mounted it in almost the stock location which is right at the driver's feet on the other side of the firewall (see pic).

I decided I didn't like the column shifter (remember, I have an automatic transmission) and decided to build a floor shifter for it. I wanted to be the only YJ with a floor shifter. I bought a conversion shifter on eBay for USD$50, but it was not made for a 4x4 because the transfer case linkage got in the way. So what I had to do was mount it farther forward than it was made for. Now this made the shifter handle hit the dash when it was in park. So we cut the handle and notched it at a 45 degree angle so it wouldn't be straight up; it comes back towards me now. Then I built a shifter plate out of diamond plate to mount it to and it works well and looks good. If anyone wants more detailed information and pictures on this part let me know, I can get them. I used my steering wheel from the 90 and all the 93 wiring harness plugged straight into it without any problems. You can buy a shifter made for a 4x4 but the cheapest one I found was USD$200, and like I said, I am cheap.

Because we moved the engine forward we had to get the rear drive shaft lengthened and the front one shortened. This only cost USD$130 with new u-joints, painted and balanced. I was very pleased.

At some point we swapped gas tanks for the 20 gallon, with fuel lines. It wasn't difficult, just had to beat on some stuff to get it out the first time. Took maybe 2 hours with two people.

After I got the dash, wiring, and steering wheel hooked up, I tried to start it. It turned over just fine but for some reason would not start. Tried everything, checked all the wiring, but still no dice. Posted on the JU board and got lots of things to check but everything was good. Finally, someone mentioned that the gas is supposed to come in the line closest to the firewall. We had switched the fuel lines back at the gas tank so fuel was trying to go up the wrong line! That was actually the biggest headache of the whole swap, and of course it was really stupid. But I can't complain since that is all that went wrong.

Finally, we put everything back together and she ran just fine. After putting the electric fan and K&N type exhaust on, I would guess the engine puts out a little over 200 HP. So I personally don't believe the small gain that a 5.0 or 350 would afford is worth the USD$3500+. Plus, when this engine dies I will just rebuild it as a 4.7 stroker and have a stronger engine than a 5.0.

The Jeep is now running great. It pulls like a locomotive because I installed the 4.10 gears from the 2.5 and its on 31's right now with a 2.5" suspension lift. It revs a bit high on the highway because of the tire size but I am not gonna complain cause I love it. I am sure I forgot things but if you have any questions I will answer them.

My Dad and I did this over the winter and there are a few things still not working, like the heater and speedo, but that will just take some time to getting around to. Overall it was a great experience, learned a lot, made my Jeep better, and made 500 bucks to boot. I really can't complain.

The unlucky donor.

The lucky recipient.

The new motor.

Regards,

Scott