I have heard rumors that the fuel injection system including the manifold from a 4.0 engine will fit onto a 4.2 258. Does anyone know if this conversion is actually possible?  

I don't know if it was in fourwheeler or jp but they bought an aftermarket efi system for a 258 i think it was around 1,500-2,000 $$$  

If you ever come back to read this than here:

These are the contents of the kit as supplied by Mopar. The kit is available over the counter through Mopar dealers.

If you own an '81-'90 4.2L (258ci)-powered Jeep, there's something lurking behind your local Mopar dealer's parts counter that will interest you. It's called the Mopar Performance Jeep 4.2 Liter Multiport Fuel-Injection Kit, and as its name implies, it includes everything you need to easily upgrade your carbureted engine to quality fuel injection. And it doesn't matter whether the engine is mated to a manual or an automatic transmission.

Some of you may chuckle at our use of the word "easily," but based on what we saw as we watched Matt Dinelli of Attitude Performance in Arlington Heights, Illinois install the kit on a customer's '89 Wrangler, the kit does indeed simplify the conversion to a level of being almost fun. Developed by Hesco for Mopar, we're told the kit is a duplicate of the system found on '91-'95 4.0L vehicles. Part of the reason it installs easily is because of the easy-to-follow, detailed, illustrated instructions and a helpful installation tip sheet that covers frequently asked questions. The kit's overall parts content seems to also have been scrutinized to allow for a significant amount of assembly to be done at the factory, so you don't have to.

 

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The benefits of the system were immediately clear as we drove the finished product about 50 miles after the install. Smooth acceleration throughout the powerband, great cold-starting manners, and performance unaffected by angles were some of the obvious benefits.

The following photos will give you a basic idea of the kit's major components and their installation during the assembly phase. Obviously, you should read and follow the instructions provided with the kit. Dinelli was installing the kit on a freshly rebuilt 4.2L engine that was prepped in accordance with the kit's installation instructions. This meant that a number of components already had been removed, like the power-steering pump, air-cleaner assembly, production emissions controls, carburetor/intake manifold assembly, fuel pump and lines, radiator, fan, distributor, windshield washer bottle, charcoal fuel canister and exhaust manifold oxygen sensor.

The kit has a street price of approximately $1,900 and requires about 13 hours to install. Clearly, the kit doesn't jump out of the box and right under the hood, but considering the significant upgrade of the install, we think that's a respectable timeframe. Once installed, the powertrain control module takes 15 to 30 minutes during first use to "learn" the best settings for your engine. You will notice improved idle quality and acceleration after this learning period. From there on out, float bowls and needle valves will be a thing of the past, and your rig's performance will be the envy of your 'wheeling friends.

This is the way our 4.2L engine looked when prepped for installation of the Multiport Fuel-Injection kit, per Mopar's installation instructions.		Begin by installing the new distributor. Follow the instructions provided with the kit to set the timing. Install the nifty combination fuel-pump block-off plate/ignition-coil bracket where you removed the original fuel pump. Install the coil with the plug terminal toward the distributor.		Install the new crankshaft damper and the pickup-sensor bracket. The bracket bolts to the oil pan using three bolts removed during disassembly. Install the pickup sensor on the bracket with the bolt provided. There should be 0.020 to 0.060 inch of clearance between the sensor and the crankshaft damper. This clearance is critical to the operation of the system.
The kit includes a new thermostat housing, coolant sensor and 195-degree thermostat. The installation instructions note that it's important that the new thermostat be used for correct fuel system operation.		Install the new intake manifold. You will only be able to reinstall one of the power-steering-pump bracket bolts and you may have to trim the top lip off of the power-steering-pump bracket to make it fit the new manifold. Do not over-tighten the manifold bolts. Bolt torque is 23 lb-ft.		This is the new kick-down linkage mount at the transmission. After installation, you should set the adjustment by ensuring that the cable ratchets to the proper zero clearance. At this point you may reinstall the power-steering pump bracket and

 

Courtesy of fourwheeler.com

 

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Very nice greeting J.J.Jeep!! I propose that joejjeeep be elected "goodwill" ambassador for this forum...do I hear a second for that motion??

Anywho....

Owning a 4.2 and desiring to inject as well, I have done exhaustive research....and if you can get the entire head from a 4.0 that will bolt onto a 4.2(with some minor drilling and tapping) and the head flows  much better than the 4.2.

Best case scenario is to get a head from I believe its 95+ up...someone correct me if I'm wrong... but those heads have the equal length intake runners and make roughly 20% more power than the 94+down heads.

Whether the manifolds match up or not....go down to the parts house and ask to see the gaskets from each and match them up...sounds feasible. 

If that doesn't work, or sounds too dificult check this guy out...he has got skills.

http://www.customefis.com/

Another option is to adapt a GM TBI system from a late 80's early 90's GM V6.

Howell makes a decent kit for this, and there is an abudance of info on adapting this system to various engines. I bought the Howell kit and then learned to modify the "chip" to get it tuned to my particular engine and climate. The kits are nice because they will come with a wiring harness/connectors which makes life much easier.

This link:

http://www.customefis.com/index.html

is a great place to start if you want to Do It Yourself (DIY). He also offers kits for Jeeps at a very good price.

Email me if you want more info.

David

David M. Ingebretsen, M.S., M.E.

Collision Forensics & Engineering, Inc.

2469 East Fort Union Blvd. Suite #114

Salt Lake City, UT 84121

dingebre@3dphysics.net