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Jeep XJ 4.0L to CJ-7 Engine / Transmission Swap


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Hi Jeepers, Earlier this year I bought a 1981 CJ7 (first Jeep) 258 Carbureted, SR 4, Dana 300, Dana 30 front and AMC 20 Rear  with 86K. I did all the preventative maintenance and minor repairs to get it running smooth (more or less with a feet of new vacuum hoses). The transmission is junk popping out of first and reverse. I have a rebuilt SR 4 ready to go in as a temporary fix to keep it on the road. I guess I have to wait to order a clutch pack until I get it apart and  measure to the get the correct size. Following the threads I think I can rebuild the D300 and have now have the rebuild kit, so I will be asking some questions.

 

I just picked up a 1991 XJ Cherokee donor vehicle from a local tow yard for $300.00 it was towed by the police for being a unsafe vehicle No windshield or insurance and I picked it up for the tow and storage bill, PO did not reclaim the vehicle.  I want to swap the 4.0 with fuel injection and the AX15 to the CJ. Has anyone else done this swap? I know I need and adapter for the AX15 to D300 as the XJ has a NP231J and I will need the computer and wiring harness. Am planning to transfer the entire hydraulic clutch system to the CJ, What else am I looking at?

 

Thanks Don

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Hi, Don...I'll jump in here, other members and owners can share their experiences, too! 

 

You're right about the adapter from the AX15 to D300 transfer case, the issue is the transfer case clocking position and making sure the spline count and stick-out length of the transmission output shaft match up with the Dana 300 input.  Contact Advance Adapters at 1-800-350-2223 for technical details and the parts list.  You can get an overview of your adapter needs at the website:  www.advanceadapters.com.

 

Engine mounting brackets should swap over from your current 4.2L/258 inline six.  Check the back of engine/transmission length issues and the 4.0L/AX15 measurements from the bellhousing face at the engine block to the transfer case.  Take into consideration any adapter thickness, too.  This will dictate the final position of the transfer case and whether drivelines need cutting or added tube length.  If so, you'll also be repositioning the transmission/transfer case mount position on the skid plate, a relatively easy task.  The torque brace pin will need relocating, too.  If there is significant movement, check the transfer case shift lever position with the floorboard opening, this may require adjustment...Let us know what you discover here.

 

The wiring can be handled one of two ways.  If separate Mopar EFI kit parts are available, specifically the wiring harness for the first MPI/EFI kit patterned after the 1994-95 YJ Wrangler factory EFI, that would be a ready made harness and include the wiring to the fuel pump near the gas tank.  (Yes, you will need a PCM-triggered electric fuel pump, it can be externally mounted like the Mopar EFI kit pump.)

 

If this harness is not available, you're left with using the harness from the XJ Cherokee and following a wiring schematic to tie all of this together.  This does require some automotive electrical savvy, it can be done, many do it.  You'll be using everything from the PCM to the over-engine harness, EFI hookups, the coolant sensor wiring, and so forth.  Each signal that the 60-way (terminal count) PCM requires needs consideration.  If there is a wiring schematic of the Mopar EFI Conversion Kit available (possibly HESCO can supply), that would be very helpful, even if you use the XJ factory wiring. 

 

Note: Your 1991 4.0L MPI/EFI is a two-rail type and requires a return fuel line from the EFI fuel rail to the fuel tank.  This is not difficult to devise, as the 4.2L likely uses a return pipe from the fuel filter to the tank with its mechanical fuel pump system.  You can mate to that piping if it's large enough in diameter or fabricate a return pipe and hoses that will join the fuel tank at the same location as your original fuel return line.  Use higher pressure EFI-rated fuel hose and Euro or EFI type clamps.  If you want to see how all of this comes together, I cover it in detail within the Jeep® CJ Rebuilder's Manual: 1972-86, available from 4WD parts sources, Advance Adapters or directly from Bentley Publishers.  Here is overview material on your subject and this install:

 

1) Carburetion Versus EFI Conversion for the 4.2L Jeep Inline Six...Should you convert your 4.2L Jeep inline six to EFI? In this feature, Moses Ludel contrasts the BBD carburetor and the Mopar Performance EFI conversion kit. www.4wdmechanix.com/Carburetion-Versus-EFI-Conversion-for-the-4.2L-Jeep-Inline-Six.html

 

2) How-to: Tuning the Fuel Injected Jeep Inline Six Stroker Motor...The Jeep inline six stroker motor with EFI or MPI develops maximum performance when tuned properly. Selecting the correct MPI injectors and matching the fuel supply system to the bigger engine and higher horsepower output require the modifications described here. www.4wdmechanix.com/How-to-Tuning-the-Fuel-Injected-Jeep-Inline-Six-Stroker-Motor.html
 
3) Jeep Fuel Pressure Requirements...Fuel pump and system pressure is different for carburetion, TBI and MPI. In this article, Moses Ludel discusses fuel pressure requirements for various Jeep engines and chassis designs. www.4wdmechanix.com/Jeep-Fuel-Pressure-Requirements.html  (This article has detailed and helpful illustrations, Don. View closely.)
 
3) Jeep CJ Inline Six Stroker Rebuild...Moses Ludel shares details about the Jeep inline six stroker upgrades. 1972-86 CJ models,1972-up Jeepster Commando models, full-size J-trucks and Cherokee 4WDs with the 232 or 258 inline six can each benefit from a 4.5L, 4.6L and 4.7L Jeep inline six stroker engine upgrade.
 
4) YJ & TJ Jeep Stroker Six Upgrade...Moses Ludel shares details about the Jeep inline six stroker upgrade for the 1991-up YJ and TJ Wrangler. When the original 4.0L inline six is needs rebuilding, consider the 4.5L, 4.6L and 4.7L Jeep inline six stroker rebuild option. Complete history and evaluation available here!
 
5) Rebuilding the Two-Barrel BBD Feedback Carburetor...The 1981-86 Jeep CJ models equipped with a 258 inline six have the Carter BBD two-barrel carburetor. Many owners and shops find this carburetor challenging. In this detailed 'how-to', Moses Ludel troubleshoots and restores the BBD to 'as new' standards.
 
I would say that your biggest challenge is not the mechanical side but rather the time-consuming wiring side.  I like wiring work, not everyone does.  Splices for EFI should be wire lapped and rosin flux soldered, covered with heavy duty or multiple layer heat shrink tubing.  Voltage readings are critical for EFI, simple butt-crimp connectors cannot assure a proper voltage reading, and the open ends of cheap splice connectors beg issues like corrosion and corrosion wicking up the wires.

 

This is a start...Pleased to add more.  Others can join here!

 

Moses

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Thanks Moses, as an old retired Navy Gunnersmate, electronics is part of training. I like analog over digital, just the way I was taught.

 As you pointed out drive shaft lengths are always part of a Swap.

 

I already ordered   Jeep Cj Rebuilder's Manual, 1972-1986: Mechanical Restoration, Unit Repair and Overhaul Performance Upgrades for Jeep Cj-5, Cj-6, Cj-7, and Cj-8/Scram it should be delivered on the 29th and I have reviewed the five videos you and Tony did on the 4.0 stroker project. I am leaning toward the 4.6 rebuild as I want a complete package rebuild before I pull the old 258.

 

Thanks for the advice and am looking forward to further dialog and sharing my pictures.

 

R/

Don

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Yes, dderrik10!  You'll likely be fine with a wiring schematic and the XJ Cherokee wiring harness.  A hint: Mopar Performance got the Mopar EFI conversion kit wiring harness down to a four-wire interface with the factory wiring on a 1981-90 CJ or YJ.  This is the reason I suggested a peek at the Mopar schematic if available anywhere...The Jeep CJ Rebuilder's Manual: 1972-86 (soon in your hands!) with the Mopar EFI kit installation on a 4.2L inline six will furnish details.  

 

Since the earlier two-rail Mopar EFI conversion kit is patterned off a '94-'95 Wrangler/Cherokee 60-way system, most components will look like your 1991 XJ Cherokee's induction and EFI/MPI 4.0L system.  

 

If you do the AX15 swap and need to rebuild the AX15, they're worth it.  I have the detailed steps (over 200 of them!) in the HD video rental available at Vimeo On Demand.  Here's the link if you need it:  http://www.vimeo.com/ondemand/ax15rebuild.

 

I'm available for questions or factory wiring schematics!  You cannot go wrong with a properly built 4.6L stroker six...Minimal cost difference over a stock 4.0L rebuild with so much to gain.  Note the tuning comments for injectors, that's a key element and relatively minor change.

 

Moses

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Good luck with the project, dderrik10!  My '83 CJ-7 has a MOPAR EFI kit that started life on the old 258.  That EFI is now sitting on a junkyard 1995 XJ 4.0.  It's got about 155K on the engine, but it still runs strong.  I didn't do the swap, but I'm happy to take pictures of my setup.  Moses will give you excellent info as well.

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