Bill's Buckets: Restorations, writing and reviews

CJ7 4.0 Engine Swap

Renix 4.0 Swap

Circumstances

The 258 cubic inch motor that was installed in my 1986 CJ7 at the factory was pretty unremarkable. Bogged down by a terrible carburetor and out-dated smog equipment the ancient non-cross flow push-rod six cylinder was fighting an uphill battle. That being said it was as reliable as old-yellar, and had enough torque to drag a full-size ford van up the street without missing a beat. With a little over 200,000 miles on the ticker, my 258 was still in surprisingly good shape. I didn’t always idle well, and it had a rear main seal leak, but it started up like clockwork every day. In fact, if it weren’t for the fact that I had to pass California smog at a test only station this year, I would have left the motor right where it was.

Alas, smog was due, and I knew that the motor was not up to the sniff test this time.

I contemplated dumping the necessary money into the motor to get it to pass. I estimated $600 at the local jeep shop would be enough to get it through. As fortune would have it, I stumbled across a cheap 4.0 motor out of a 1990 Jeep Cherokee on craigslist. I had heard of people doing this swap without too much trouble. So I did a little preliminary research on the swap, then went ahead and bought the motor for $250. It also came with a computer, and box of wiring harnesses.

When I read up on the 4.0 swap I found several people who said it could be done in a long weekend. As you will see in this right-up, largely due to budget and space constraints, it took me a lot longer than a weekend.

(Left: My Old 258)

The New Engine

I was on a very tight budget for this swap and knew I would be relying heavily on junkyard parts. This also meant that I couldn’t rebuild the 4.0 motor. So I just took the sellers word that the motor was a good runner (even with a 130k on it) and only needed a rear main seal. As it turns out the motor first came out of a Cherokee that was in an accident. Then it was swapped into a Commanche that rolled. After acquiring the motor I noticed the valve cover was shattered—from the rollover no doubt—but other wise seemed to be in ok shape. This spawned my first trip to the pick and pull. I found a nice polished aluminum valve cover, which I promptly took home and put on the motor.

(New motor with shattered valve cover)

My next task was figuring out the clutch and transmission arrangement. My CJ7 had a T5 manual transmission. This tranny has a separate bellhousing which bolts right up to the 4.0 block. After doing a bit of research I decided to stick with the T5 transmission from the 258. I also decided that I would use the original style Crank Position Sensor (CPS), and modify my existing bellhousing to hold the sensor. It was very helpful that my new 4.0 motor came with an AX-15 bellhousing with a CPS mounted in it. This allowed me to make a template so that I could get the sensor location spot on in my T5 bellhousing. It should be noted that CPS relocation kits are available from Hesco for Renix injected engines, but people have had varying results, and I decided that the safest bet was to modify my bellhousing (Novak will do this for you if you send them your bellhousing, I don’t know the cost). Because I chose to mount the CPS in the bellhousing I would need to keep the 4.0 flywheel on the motor. As it turns out this would be a good thing because it meant I could run the smaller more powerful 4.0 starter as well (the starter and flywheel need to match up for smooth operation). The Renix 4.0 flywheel has a unique pattern cut into it that triggers the CPS. However the clutch disc, pressure plate and throw-out bearing that were used were all 258 parts purchased new at Napa Auto.

The pilot bushing that came out of the 4.0 flywheel was actually two separate pieces, an inner and an outer bushing.

This made things confusing when it came time to replace it. The pilot bushing I ended up using was specified for a 258 and came with my clutch kit. I also bought a second bushing from Kragen before I knew that the 258 bushing would work. The bushing I bought at Kragen was way too small, while the Napa bushing that came in my clutch kit fit snuggly in place. I read that a lot of people have to machine the bushing down to the right size, but not in my case. If you have the time you should measure the opening with a caliper, and double check it against the part at the store.

(Left: Here is a shot of the 2 pilot bushings I purchased. The thicker one on the left ended up being a perfect fit.)

CPS bellhousing modification

After installing the new clutch on the motor, it was time to modify the T5 bellhousing to accept the Renix CPS. Because I wanted to have the 4.0 ready to go in before I pulled the old motor, I had to buy a second T5 bellhousing to modify. I made a template using the AX15 bellhousing that came with the 4.0, and figured out exactly where the sensor needed to be in my T5. I then cut a window in my bellhousing, so that a small section of flywheel would be exposed. I made some aluminum spacers to get the depth properly set for the sensor. I had these spacers Tig welded to the bellhousing. I also had to modify the sensors metal bracket in order to make it fit. I chopped a tiny bit off of one side, then slotted the holes so that it could be adjusted. Then I test fitted it to the motor and screwed it in place with locktite in the location that seemed best.

(Top view of the CPS)

(In this side view of the sensor you can see that the bracket is shorter on the left side, this is where it had to be chopped a bit)

Disassembly

I started by disconnecting the battery and draining all the coolant out of the radiator.

Because I had limited clearance in my garage and because it’s really easy to do, I removed the front bumper, grill and radiator from the Jeep to make engine removal much simpler. I disconnected all the fuel lines that were running to the engine and capped them off. I drained the power steering pump and disconnected the lines from the motor. Then I disconnected all the wires that were running to the motor. I also removed the starter to gain extra clearance.

(258 still in the Jeep)

Next I removed the clutch linkage, removed the bolts holding the bellhousing to the transmission, and loosened the motor mounts. With the hoist supporting the motor, I completely undid the motor mount bolts. And with some gentle coaxing, the old 258 came right out.

(Empty engine bay, with old 258 sitting in front.)

4.0 Prep Work

With the old motor out of the CJ, I turned my attention to setting up the 4.0 and getting it ready to put in. I already had installed a new valve cover and clutch assembly, and I wanted to do the rear main seal with the motor in the car (I didn’t have a proper stand) so the last detail was moving the 258 motor mounts onto the 4.0. The motor mounts basically bolt right up. The only problem is that on the drivers’ side of the motor, one of the holes you need for the motor mount is occupied by the knock sensor. I moved the knock sensor forward to the next closest hole in the block. The hole had to be drilled out a bit bigger and tapped to accept the knock sensor (Use a 12mm by 1.25 tap). I also had to get a metric sized bolt to go in the hole where the knock sensor used to be. The bolt was a short 12mm by 1.25. After that the motor was ready to go in.

(Here is the drivers’ side motor mount. Notice the larger 12mm x 1.25 bolt where the knock sensor used to be. Also notice the empty hole forward of the motor mount bracket. This is the new location for the knock sensor)

(The blue/green colored sensor is the knock sensor in its new location without its insulation on)

(just about ready to drop in)

Installation

I installed the motor by myself and it was a bit of a bear. I recommend a helper if you can find one.

I left the transmission in the car but removed the driveshafts so it could rock back and forth on its soft mount, this helped to line up the splines of the tranny with the clutch. I got the motor to slip over the transmission input shaft, but it didn’t want to go all the way on. After making sure that nothing was caught or binding, I got some long bolts and stuck them through the transmission and threaded them into the bellhousing. I slowly tightened down each bolt a little at a time, working in a circle, and was able to pull the engine all the way into place. I then lined up the motor mounts, and lowered the motor off of the hoist, tightened all the motor mount bolts, and bellhousing bolts, and called it a day. One additional note: If your CJ has a power brake booster clearance can be a bit tight on that side of the motor. I had to bend the unused cruise control bracket out of the way in order for the motor to fit without contacting the booster.

(Left: A shot of the new motor in place)

Odds and Ends

I was extremely relieved to have the motor in place, but there was still a ton of work to go. My old 258 had a nice big clutch fan that I wanted to run on the 4.0. Every place I checked said that this wouldn’t work because the 4.0 used a reverse rotation water pump (pump rotates in the opposite direction as the crank). Well as it turns out late CJ’s that had serpentine belts also ran a reverse rotation pump. However the fan that came with the motor was from a Cherokee and located right under the AC and above the alternator, and it simply wouldn’t fit in the engine bay. So I removed this fan, and bolted the naked pulley back in place. My CJ fan had a different bolt pattern than the Cherokee water pump so I went to Napa and bought a water pump for ’92 Wrangler (must be a 4.0 equipped wrangler), then I went to the dealer and bought a matching water pump pulley (I tried my old CJ pulley but the depth was off and it rubbed on the water pump). I had to put the tube (pipe fitting) for the heater hose from my CJ onto the Wrangler water pump. It just threads into place, but be sure to use thread sealing compound or tape. I bolted the water pump in place and put the fan on and in fit great. I sent my old CJ radiator out to have a leak fixed, and have it cleaned, then I put on new radiator and heater hoses and bolted the radiator and nose of the Jeep back into place.

(A shot of the new pulley with the old CJ fan bolted on).

The power steering pump also needed to be hooked up. I used the original CJ lines and bent them around the new pump so they fit without being in the way. The threaded line went in without too much difficulty.

(The bent power steering hard line)

I put the oil pressure sender from the 258 onto the 4.0. It threaded in place just fine and connected into the wiring harness without trouble.

I mounted the Manifold Absolute Pressure (MAP) sensor on the firewall right behind the valve cover. I used a stock Cherokee sensor and bracket that I grabbed from pick n’ pull. This mounting location is similar to its location in a Cherokee, and allowed me to use the original hard vacuum line.

(The MAP sensor has the green plug attached to it)

For the throttle cable I used a Cherokee (XJ) cable (another junkyard item) which I had to shorten a bit. I used crimped rivets to attach the cable at the pedal end, the cut-off the excess length.

Fuel System

When I did my research I got conflicting answers on how much fuel pressure the Renix system requires. It seemed like it ranged between 45 psi to 75 psi. Because of my tight budget, and mixed reviews I decided not to buy an E2000 pump which is commonly used in this swap. Instead I went to the pick n’ pull and got a high pressure externally mounted Bosch pump from an ’87 BMW 5 series car. This pump is rated at around 100 psi and is certainly capable of filling my fuel needs, plus it was much cheaper. I decided to mount it on the passenger frame rail back by the tank. I mounted it so that it is lower than the tank and as close to the tank as possible. This will help keep the system primed and prevent the pump from prematurely burning out. It should be noted that many high pressure external mount fuel pumps are meant to run in conjunction with low pressure in tank pumps to prevent burn out from the pump running dry, by keeping the pump mounted below the tank, the risk of burning the pump out is reduced. The Bosch pump also has an anti backflow valve built in to keep fuel from running back into the tank. I mounted the pump using an old cylindrical ignition coil mounting bracket and wrapped it in thick rubber to isolate the vibration and quiet the pump down. Directly in front of the pump I ran a high pressure fuel filter, and between the pump and the tank I ran a low pressure pre-pump filter.

(High pressure filter)

(Bosch pump)

(Pre-pump filter)

It is very important that you only use EFI rated fuel hose for anything between the fuel pump and the motor. If it is between the tank and the motor, you can use standard fuel hose, as the pressure is significantly lower.

The fuel return line for the 4.0 is 5/16” and the CJ factory return line is 1/4”. After talking to another jeeper who used the 1/4" return line for his 4.0 swap I decided to do the same. Just to be safe I used EFI rated fuel hose for all non-metal sections on the return line as well.

I replaced all the old hose going to the gas tank with fresh new hose and used high quality hose clamps to make sure everything was tight and would last.

I used the factory steel fuel hose from a Cherokee to connect up with the motor. These hoses have special fittings that clip into the fuel rail. I had to bend the feed and return lines to route them in the engine bay so that they were out of the way. The majority of the fuel system is steel line, and rubber hose was only used in short sections to join the steel lines, the filters and the pump.

I am in the process of making a cover plate for the pump and filters, but I feel that they are out of harms way where they are and it will be mostly to keep things looking tidy.

Wiring

The wiring process was easily the most time consuming and difficult part of the swap.

Because I was a cheap skate I decided that I could do it without a Factory Service Manual (FSM). Fortunately with the help of the Yahoo renix group, and several other online resources I was able to get all the wiring diagrams I needed. Several people even sent me photo copies from the original FSM.

My 4.0 came with a “wiring harness” but when I laid it out to figure out where things should go it became evident that it was incomplete.

I ended up going to the pick n’ pull (a recurring theme here) and removing an entire harness from an ’89 Cherokee. There are slight differences in the harnesses from ’87-’90 but they should all work fine on any motor as long as they are complete.

I only used the engine side of the harness up to the bulkhead connector. I did not need the fuse box or interior harness from the Cherokee because I was running stock CJ gauges, heater, fan etc…

My late model CJ actually had a computer. So I decided to mount my new computer in the same location (inside the cabin above the heater ducting on the passenger side). Conveniently there was also already a good size hole cut in the fire wall for me to run all the wires through. I mounted the coil on the passenger side fender, the starter relay was mounted on the batter tray, and the three relays necessary for running the motor were mounted on the fender as well.

(Coil, starter relay, diagnostic connectors in yellow, and other misc. relays.)

(A little messy but it all works)

Once you have the wiring harness attached to the motor—all the sensors plugged in, the injectors hooked up etc—it is not that hard to patch it into the CJ harness at the bulkhead connector. There are only a couple wires that need splicing. And of course you will have to bring the wiring from the fuel pump up to the engine bay. You will need a main power feed wire, an ignition crank wire, and a crank and run wire. I have an ’86 CJ7 and will give the cavity locations for my specific model, but it is easiest if you get a copy of wiring diagrams for your CJ and the vehicle that your motor came out of.

1986 CJ7 w/258 1990 Jeep Cherokee w/4.0

EY- Red 10ga- Battery feed D1-Red 12ga- Battery feed

AX-Lt Blue-14ga-start H2-Green 14ga-start

BW-Red W/Tr 10ga-ignition/coil power B6-Yellow 14ga-ignition power

I tested the remaining CJ cavity to see which wires came on with the ignition, and I wired the fuel pump to a wire that became hot when the ignition was on. I believe it was cavity CX –Red 14ga- computer on the CJ to C4 Orange/black 14ga fuel pump.

I used the old CJ gauges and transferred the oil and temp senders from the old 258 onto the 4.0 so that I could use the old CJ wiring for the gauges.

The only remaining wiring is to ground the park/neutral switch if you are using the ecu from an automatic transmission donor vehicle. If you pull out the ecu and look the connector pins you can find the wire in cavity C4. This wire needs to be grounded in order to let the engine crank over and run. In Jeeps fitted with the auto tranny this simply made sure the car was in park or neutral before it would allow the driver to start the car.

Starting the motor

After double checking all fuel lines, and electric connections, making sure the engine had oil and water, and making sure I had a fire extinguisher near by, I put new gas in the gas tank, and hooked up the battery.

I unplugged the coil, and cranked the motor over until I go oil pressure, which took about 5-10 seconds of cranking. Once the pressure came up, I checked to make sure I had no fuel leaks, then hooked up the coil and cranked it over. The motor fired right up, went up to a fast idle then dropped right down to a slower idle. At this point all I had was a straight pipe on the exhaust, so I didn’t run it too long to spare my neighbors the noise.

I cleaned up the garage and decided to take it out for a spin. So I fired it up again, and tried to put it in gear but it wouldn’t go it. With the motor off it engaged just fine, but it refused to go in with the motor running. I double checked the linkage and it appeared fine. So I did a little research and was told to try starting it in gear with my foot on the brake and the clutch depressed. The theory being that the pilot bushing was seized on the input shaft of the tranny, and starting it in gear would bust it loose. It worked. I held my foot on the brake and clutch, and let it run for a bit to open up the pilot bushing a bit, then I took a victory lap around the block. Everything seemed to work well.

The next day I went to the muffler shop and had a full exhaust system complete with catalytic converter put on. Then I made an appointment with the smog ref.

Smog Ref

I had to install the original Cherokee style air box in my CJ to get passed the California Smog Referee. The box doesn’t fit under the hood, so I simply installed it then bungee corded the hood down. It didn’t look pretty but it was effective. Amazingly I breezed through the Smog Ref visual test, and passed the sniffer/rolling road test with flying colors.