[doushenhimer]

Hello.. I'm a 89 yj with a straight 81 AMC carbureted 4.2L. I need to fuel inject it for crawling, and have found an 93 4.0L fuel injected. My question is, if the idea of swaping the rail and computer to my 4.2 will she run and function? Please and thank you!

 

[havasu]

You will need more parts, such as a crank position sensor and an on line electric fuel pump. They can be located at:

http://www.hesco.us.

 

[Chris]

I believe you will have to swap the head to but I am not 100%, Maybe Rik will chime in, he has done this swap.

 

[RikRotorhead]

Chris is right, you have to do a head swap. The intake is different and the way the air enters the valves is different in a FI head. There is a lot involved but it's doable. CPS, alternator, distributor, coil, fuel tank (needs the electric pump), high pressure fuel lines, wiring modifications, smog system modifications, and a few more things.
Huge power gain doing the swap tho'.

 

[havasu]

My YJ has f/i and the head is the same, but yes, there is a new intake manifold. The PO of my jeep purchased the full f/i kit from Hesco, which runs ~ $2500 but there are cheaper versions out there.

 

[Chris]

Yes there are kits that use the factory head like the one havasu mentioned and the cheaper Howell kit. But I think he is looking at junk yarding it.

 

[havasu]

Dropping a junkyard 4.0 F/I would probably be the cheapest and the quickest.

 

[Chris]

Yeah me personally would probably drop the whole motor instead of doing the head swap.

 

[RikRotorhead]

Swapping a 4.0 FI motor still requires the wiring harness, computer, new fuel tank, high pressure fuel lines, CPS on the trans, new alternator, and new smog equipment plus other mods.

The easiest and cheapest way to go is the Howell FI system like Chris mentioned. It's a complete kit, direct swap for your carb, comes with the computer, CA smog legal, and you can use a external fuel pump. I think it comes with it.
The Howell kit is basically a new manifold base plate you put on your existing 4.2 stock manifold and it uses an early nineties Chevy 4.3 liter throttle body. They work really well and are simple. Couple hours and you are done.