Swapping in a 4.0L MPI Engine
Short Cuts

By: Robert Hyde - 4/2001

The 4.0L engine.

The 4.0 swap is about the easiest swap that can be done to the CJ7, at least in my opinion. I've have listed below the parts and major procedures. As with any modification you may encounter different scenarios pertaining to your vehicle.

I bought my 4.0 motor out of the classified ads. It only cost me $450.00 including the alternator, power steering pump, air conditioning pump, (converted for on-board air) which is a good price. Normally, you can expect to pay anywhere from $500-$1000. It's a good idea when looking for a motor to ask about getting the computer (ECM) and wiring harness. If you can't get these items you can get them from Hesco for around $350.

You will also need to get a external fuel pump, or you can go through the hassle of getting a wrangler one and dropping you fuel tank and sticking it there. The external fuel pump is mounted near the front of the gas tank skid plate along with a fuel filter.

Another key part of the swap is the crankshaft position indicator. I chose to buy this from Hesco rather than drilling up my bellhousing. The Hesco kit comes with a new vibration dampner with the CPI that mounts using 3 bolts on the front of the oil pan. It is real easy and convenient to hook up.

I mated my new 4.0 motor to my stock T-5 transmission. At first I was concerned with a new pilot bushing because the new motor came from a Cherokee with an automatic transmission. The pilot bushing from a T-5 transmission does not fit into a 4.0 motor because the diameter of the hole in the crank shaft too big. You can get a special pilot bushing from Advance Adapters for about $10.00 or you can machine down the stock pilot bushing.

Follow along as a I go over my fun filled weekend. I did try to write most of what I did, but if I did forget to write something it does not necessarally mean I didn't do it. I tried to write ablout the major wrenching and problems I encountered and over came.


The Jeep.

You should allow at least a full weekend to do the swap. I started on a Friday evening, cleaning my garage and making sure I had plenty of room work. I would be dealing with two motors on the ground at the same time, so I needed room to work. Really, you do not have to do this is any specific order, but I did start out by disconnecting the battery, draining the coolant, then removed the following items: upper and lower radiator hoses, fan and fan clutch, radiator & shroud, starter, and engine ground cable. Take the nut off of each motor mount, remove clutch linkage, flywheel inspection plate, then disconnect the fuel line, put a screw driver in the hose and put a clamp around it, pull off the fuel line from the carb going to the charcoal canister. Take the air cleaner assembly off, don't forget to put a rag or something to cover the carb.

While pulling the wires off the motor I used some manila folder labels to label the wires. There are about six wires coming out of the drivers side firewall that you will use on the new motor, red/white and light blue are your ignition wires, they run to the small posts on your starter solenoid. There is also a brown/tan wire going to the heater motor, purple/white going to the temperature sending unit, purple wire going to the oil presure sending unit, orange wire going to the cheesy hood light. The thick red wire (10 gauge) is your power wire for your fuse block inside your jeep. This wire runs to your starter solenoid and it has a constant 12 volts.


I woke up early, because I knew the day would be a long one. As there is no instructions for this swap, I dove right in. Having gone over what I did last night, I figured I was ready to yank out the old reliable 258. I positioned the cherry picker over the motor and hooked up the chains, the Chiltons manual said not to pull the motor by the manifold. Well, I challenged the manual and hooked one chain to the manifold the other chain I bolted to the front right side of the motor where there are a few threaded holes to use. Leaving some slack in the chain, I went down under and unbolted the engine mounts. The hard part was removing the bellhousing bolts. The socket extentions and universals sockets I got for my birthday really helped out! I placed a bottle jack under the transmission along with a jack stand.

The exhaust was next. I tried to unbolt the flange, but ended up breaking one bolt. This wasn't a big deal because the exhaust needed to be customized to fit the new 4.0 motor anyways. I went ahead and broke out the hack saw and cut the rusted exhaust pipe about 3 inches before the transfer skidplate This will leave enough pipe exposed so a new piece pipe can be weled up to the 4.0 exhaust manifold.

Because I am doing this swap by myself, I knew the hardest part would getting the 258 separated from the T-5 trans. I applied a little lift on the engine to get the motor off the motor mounts. One of the motor mounts was so old, it just fell apart. I went down under and used my bottle jack to lift the transmission up a little bit. After that, I just stood on top of my winch, I then began to shake the motor violently. After about an hour of raising and lowering both the motor and trans, a sigh of relief came over me as the engine just about knocked me off the front of my Jeep. A scream of joy came out of my mouth, which caused my wife to run outside to see what happened. She thought something fell on me.

Now trying to lift the motor out, I had stumbled on something I forgot to take into consideration. I have a 4 1/2 inch lift on my Jeep and the cherry picker did not have enough lift for the engine to clear the grill. I had to play around with that a while, so if you have a lift, take your wheels off and set it on some jacks stands or make sure cherry picker has a tall jack.

Dropping the 4.0L engine in the engine bay.

You will have to manipulate, lift and lower, the engine to get it separated from transmission. You will also have limited clearance between the firewall and the clutch/pressure plate, but with minor scraping of the clutch/pressure plate the motor can be extracted. Watch any wires that might get pinched by motor wanting to lean into the firewall and hood.

Once I had the motor on the ground, I took the flywheel off and raced down to the machine shop. They put a new starter ring gear on and resurfaced it for about $50.00. When I got back to the house, ignoring my hunger pains, I installed the 4.2 flywheel onto the 4.0 motor, with the new flywheel bolts purchased earlier. The Chiltons says do not reuse the old flywheel bolts, I didn't want to challenge that one. I used some red lock-tite and torqued the bolts. Next, I installed the Advance Adapter pilot bushing and the Centerforce II Clutch. My engine was looking good, and it was just about to be dropped in. I replaced all of the springs for the clutch fork and put on the new throwout bearing lubed with some white lithium grease.

With engine compartment empty, it was a good time to reroute the fuel line. I purchased some high pressure rubber fuel line, remember you are going to fuel injection now, so do not go cheap on that. Take the old rubber hose off the hardline and install the new hose routing it along the front, but underneath the grill, use some zip strips to keep it out of the way. I will be replacing this hose later on with stainless steel line once I get the funds. I wich I would have had more time to really clean out the engine compartment.

Also mount the ECM (computer). I mounted mine above the charcoal canister on the firewall.

Before installing the 4.0 motor and while the 4.0 motor is on the ground, go ahead and install the new crankshaft dampner. To save you time and possiblity of damage, go to an Auto-Zone and get a pulley puller. I did not install the CPI until the motor was installed. I didn't want to break it while installing the motor.

Since I prepped the 4.0 earlier, (changed the oil and filter, new water pump, spark plugs and wires, and serpintine belt) it was ready to be dropped in, I found out that it is easier to leave the Hesco wiring harness off the motor until the motor is installed in the Jeep. Also, leave the motor mounts out too, this will allow you more room to jockey the motor up and down while lining it up with the transmission, and I thought taking it out was difficult! After about hour or so, the motor was successfully mated to the T-5. It was getting dark, and I was tired and cold, so I called it quits. I felt I had accomplished a lot.


I installed all the bellhousing bolts, the starter, and flywheel inspection plate, and I hooked up the clutch linkage, torqued the motor mount bolts making sure to hook up the chassis to engine ground wire.

Next, hook up the Hesco fuel lines to the fuel rail. These are pretty cool, just snap it on. I had to cut the other ends shorter to get them to line up to the fuel supply line and the return line. Make sure these are connected right.

Next, I installed the radiator and used the stock hoses, fan, and fan clutch. Since this was a Cherokee motor and the fan was mounted to right side of the motor, when I replaced the water pump, I got a waterpump, fan and fan clutch for a 93 Wrangler (reverse rotation). I also had to get a new serpentine pulley for the water pump, the fan clutch bolt holes for the Cherokee water pump and pulley are spaced wider than a Wrangler. I got the water pump and fan clutch at PepBoys, the fan and pulley I had to deal with my local wrecking company. After all that, I topped the radiator off with coolant.

Crank poistion indicator (sensor) off the harmonic balancer.

To install the Crankshaft Position Indicator, I removed the three bolts on the oil pan and using the new longer bolts supplied by Hesco, mounted the CPI. There should be about a papers width between the CPI and the dampner.

I started on the wiring harness, it is dummy proof, everything is labeled, even the injector plugs. Mount the two relays on the firewall. You will have to purchased a MAP sensor and Oxygen sensor. Mount the Map sensor next to the relays, I worked my way around the motor hooking up everything and double checking it. You will have one long wire loom that needs to go back to the rear of the Jeep. This is your fuel pump and vehicle speed sensor plugs. You will hook up the Oxygen sensor later.

I mounted my fuel pump and filter on the rear crossmember, using the bolts that hold the gas tank skid plate on. After loosening the fuel line hardware I cut about 18 inches of hard fuel line out, I had seen a real small pipe cutter at Wal-Mart for a buck and a half that would of really come in handy. Before mounting the fuel pump, I hooked up the two wires from the wiring harness to the fuel pump, then put a touch of silicone on the ends to waterproof the connection. After that, I went ahead and mounted the fuel pump and filter as an assembly.

The external fuel pump and filter just in front of the fuel tank. Notice that I used the orginal gas tank skid plate bolts, so no drilling is required.
Wiring in the starter solenoid.
New fabricated exhaust with O2 sensor.

To install the vehicle speed sensor, unscrew speedometer cable, screw vehicle speed sensor on, screw speedometer cable to vehicle speed sensor, connect the plug from the wiring harness. Go back now and tie the wiring harness out of harms way.

Were getting theres. Now you know those wires you labeled with the manila folder labels, well hook them up. You will have a red wire and yellow wire from the Hesco wiring harness. The red one needs to be hooked up to 12v constant. I hooked mine to the constant 12v on the starter relay/solenoid. The yellow one hooked up to key on 12v. There are two wires on the wiring harness that are labeled, check engine light and tach. I bought a round 1/2" light and mounted it in my dash. Although this light does not have to be hooked up, except if your in California, it is useful because you can get your trouble shooting codes from it.

You can use your old power steering hoses, they will thread into the cherokee power steering pump. The hoses are barely long enough. Once connected, fill the power steering resorvoir.

Well I was anxious to start the motor, but I had to deal with the exhaust. I had to wait to see if all my labor and hard work paid off, it was 3:00 p.m. on a Sunday and I knew nothing would be open. My Jeep was facing nose first in the garage, think, think, think, nothing I could do about the muffler shop. I decided to get the Jeep turned around, so I backed the old Motor Home down the driveway and hooked up the strap. I never thought I'd see the Jeep strapped by an RV. I pulled the Jeep out of the garage and hooked it up the RV via the tow bar.


I know, I know, Jeep engine swap in a weekend, things come up. I drove the R.V with the Jeep in tow into work that day. On my lunch hour, I dropped the Jeep off at the local muffler shop. I did not want to go to Midas or a name brand place, those guys just would not understand what I wanted, besides I'm in California, and didn't want to hear the crap about legality, although this swap is legal in California. So, I told Jack what I wanted, a piece of pipe welded onto the stock pipe, then going up to the exhaust manifold with an Oxygen sensor nut welded on the pipe. It was a perfect fit, he even bolted it together with a new exhaust flange gasket.

After work, I put the oxygen sensor in that I had purchased from PepBoys, and plugged in the final plug. Now the moment of truth. After double checking everything, and I mean everything, I hooked up the battery cables. Wow, no smoke!

While climbing out from under the Jeep and on my way to the drivers seat, reaching in my pocket to get the key, I was going through everything again in my mind. This was the first time I had replaced a motor, and I did it by myself. I turned the key to the first position, acessories on. I heard the fuel pump start and then shut off. Good news there. I proceded to turn the key to start. The motor cranked over and quickly started. It was going to at about 1600 rpms and then it settled down to about 800 rpms. The idle was smooth, I quickly ran to the front looking for leaks (fuel, oil, and water). I was amazed at how quiet the mortor was running. I went ahead and kept checking everything until the motor was at running temperature, about 180 degrees. I got back in the drivers seat and took it for a spin. Wow what a difference in pick up! You can really notice the extra horses.

The 4.0L badge

Over the next couple of days, you will want to double check everything. Tighten bolts, check the wiring harness, and a general overall inspection. The Centerforce II clutch, in my opinion, is definitely worth the extra bucks. I have had no clutch slipage in a number of 4 wheeling enviornments, snow (deep) and rock crawling. (Rubicon, Fordyce Creek)

After having doing this swap, all I can say is this is one of the best things I have done to my Jeep. All around performance gains, (over the 258 of course), although I do miss the lower end torque that the 258 had. The fuel injection has compensated for that. I guess I could rebuild my 258, then put the 4.0 head on it, but thats another story.

Below is a list of parts that I used, where I got them, and how much I paid for them.

1.4.0 motorClassified AD$500.00
2.Centerforce II ClutchPerformance Auto Supply$256.59
3.Fuel Pump w/filterHesco$149.00
4.CPI and dampnerHesco$289.00
5.Fuel LinesHesco$50.00
6.Computer (ECM)Hesco$167.00
7.Wiring HarnessHesco$179.00
8.Vehicle speed sensorHesco$65.00
9.MAP sensorPepBoys$49.00
10.Oxygen sensorPepBoys$48.00
11.Pilot bushingAdvance Adapters$10.00

Small parts list:

Here is something that you can't buy, but you need it, "PATIENCE" don't rush yourself.

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