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How to wire 4.0 into FSJ

G

GWag87

NAXJA Forum User
Location
lyncburg
I'm swapping a 94 4.0 into an 88 Grand wag.

I have all of the mechanical stuff covered. The motor is bolted to the stock tf727 and I modified the frame mounts to accept early I6 Wagoneer motor mounts.

My questions come in at the wiring part. ... I don't know where to start? Should I use the 4.0 firewall bulkhead connector to plug the engine harness into and connect the fsj wires to the bulkhead behind the dash?

Or

Wire the 4.0 harness into the fsj bulkhead?
 
Look around on LT1swap.com for a primer on how to stand-alone an engine. It's all chevy related but the principles are the same.
 
some options:

1) Put a carb on the 4.0L

2) Do your own FI with a simplified setup (like a Megasquirt or another off-the-shelf kit)

3) Install the XJ computer and full wiring harness

As I understand it, the 88 was still carbureted and did not have any kind of computer whatsoever, so #2 is probably what I would do, since those kinds of systems are generally setup for piggyback installs. #3 has some expectations (esp the CPS) and you can avoid that stuff if you use an off-the-shelf controller.
 
I'd be really thinking hard about doing a megasquirt setup, walk away from the closed ChryCo PCM so that you can do whatever you want in the future.
 
Any engine swap, that is a modern engine is gonna be a huge pain in the ass. Even the some of the best wrench turners can do that kind of stuff. Its scary, complicated and a shitload of knowledge is necessary. I'm I'm the same boat as you.

I have a MJ buggy, but the guy who owner it before me put a 4.0L in it..
And its just not right. The wiring is all spaghetti and looks terrible, and the engine must have a blown head gasket because it runs way too hot.

I would like to put a Chevy Vortec 4.8L or 5.3L or whatever in my Jeep, but I cannot do it. I can build chassis, links, fab, weld, bend tube, design.. But I have no clue how to go about an engine swap.

So... I'm gonna gut my entire Jeep, buy a $1500 crate 350 from Summit, and a 700R4 trans... And swap in a 3 wire Gen 1 engine on propane because its basic, easy to understand, and not overly expensive. Rock bouncers run on Old V8s and propane, so it'll be fine. Yes its dated technology, but its fine for my buggy.

Why not just put a fresh 360 in your FSJ and do propane? Why do you want a 4.0L? A FSJ is a Big heavy rig man... I'd want a V8 in it if was my rig.
 
barillms said:
Any engine swap, that is a modern engine is gonna be a huge pain in the ass. Even the some of the best wrench turners can do that kind of stuff. Its scary, complicated and a shitload of knowledge is necessary. I'm I'm the same boat as you.
Click to expand...

False.

I was only ever half-bright and that was many, many beers ago. I still wired up an LS swap and got it running.
 
barillms said:
Any engine swap, that is a modern engine is gonna be a huge pain in the ass. Even the some of the best wrench turners can do that kind of stuff. Its scary, complicated and a shitload of knowledge is necessary. I'm I'm the same boat as you.

I have a MJ buggy, but the guy who owner it before me put a 4.0L in it..
And its just not right. The wiring is all spaghetti and looks terrible, and the engine must have a blown head gasket because it runs way too hot.

I would like to put a Chevy Vortec 4.8L or 5.3L or whatever in my Jeep, but I cannot do it. I can build chassis, links, fab, weld, bend tube, design.. But I have no clue how to go about an engine swap.

So... I'm gonna gut my entire Jeep, buy a $1500 crate 350 from Summit, and a 700R4 trans... And swap in a 3 wire Gen 1 engine on propane because its basic, easy to understand, and not overly expensive. Rock bouncers run on Old V8s and propane, so it'll be fine. Yes its dated technology, but its fine for my buggy.

Why not just put a fresh 360 in your FSJ and do propane? Why do you want a 4.0L? A FSJ is a Big heavy rig man... I'd want a V8 in it if was my rig.
Click to expand...

Sounds like you need to do some research. You can easily do the simple carb swap that you are speaking of but I personally like the computer and FI setup because it usually runs smoother in all conditions and angles. It is not as involved as I think you were led to believe. You just have to make sure you have all the parts and wiring harness, be somewhat savvy with electrical stuff, and take your time.

FYI- Most competitive rock bouncers have FI set ups now. The throttle response is sooooo much better. My personal favorite is Tim Camerons rig.
 
propane does't care about carb angles.

I vote for swap the factory ECM with the 4.0.
megasquirt doesn't jive with the factory 4.0 stuff, so you'd have to come up with a front mounted timing wheel like the hesco bits to get to 36-1.
unless you're planning on doing something with boost in the future the stock ECM will do fine. 94 is ODB-I, so use the factory manifold and 02 sensor and you're good. No need to worry about catalyst efficiency, evap systems and all that.
 
I don't have any indecision on the parts i want to run. I'm going to run a factory harness with an obd1 4.0 pcm.

My purpose for this thread was to gather info on the best way to make my configuration of choice work. So far Mustang shooter on fsjnetwork has provided very good technical support. He has done this swap and is being very helpful

No carb or stand alone efi for me. I'm done with carbs on my wheelers and would rather keep my parts selection to things I can find in the junk yard or local parts store.
 
Last edited:
You will need the XJ's under hood wiring harness, ECU, PDC and all the sensors. Once you get all the stock wiring and sensors it is actually pretty simple. The OBD-I setup needs about 5 wires to make the 4.0 run. A couple hot wires and a few grounds. That's it. Get the FSM for the year XJ donor you plan to use and read it and follow the power wires. You will see that the PDC gets power from the battery and then powers pretty much everything else. The fuel pump will run through the fuse panel under the dash. You will need the wiring schematic for the FSJ also.

I put a 5.2 in my 86 MJ using a 93 ZJ under hood harness, 94 XJ dash harness and the stock rear MJ harness. If I can get a FI V8 running a 4.0 can't be that difficult.
 
Thanks shelbyluvv. It's very assuring to hear you recommend this method of wiring.

I've talked to a member from another forum and this is exactly how he wired an obd14.0 into a scrambler.

This weekend I had the chance to look under the hood of a running 94 wrangler with 4.0. After looking at the factory wiring I gained a much greater understanding of how I'm going to do this wiring project. Thanks again guys/gal's I'll be back with more ?s soon
 
shelbyluvv said:
The OBD-I setup needs about 5 wires to make the 4.0 run. A couple hot wires and a few grounds. That's it. .
.
Click to expand...

this............ also do a Google search on "five for fire" it will bring up a bunch of stuff for reference.
it's easier than alot of people think.
 
I'm starting to learn that it's pretty simple. I still needed help realizing that from people who have done it before.
 
Most people are scared of wiring. It is nothing really. I just installed a 4.3 Chevy TBI setup on a CJ7 with a 258. I had a bunch of people saying it would not run.

The ChryCo OBD-I system is a very user friendly injection setup. I have a good feeling you will be really surprised how easy it really is once you start striping the harness out.
 
The PDC allows the XJ harness to be self-contained but there is some bi-directional stuff that will still need mapping (things like CEL and engine gauges, although less of a risk with jeep dashboard). Depends how far the OP wants to go with it. Really should get FSMs and see what the cab needs from the engine and vice versa.
 
I have a fsm for a 95xj. The 4.0 wiring should be the same as my 94 4.0 from an xj. I will wire in universal cel and aftermarket guages for everything that won't jive with my fsj gauges.
 
You could just research the values for each gauge and replace the senders. That way you retain your factory cluster.
 
You may be able to thread the stock senders right into the 4.0 locations. I can't see them being that much different in thread size. If they are different threads you can pick up brass adapters at Lowes or Home Depot to make them work.

What is the plan for the fuel pump and fuel gauge sender? That could be the biggest hurdle to cross.
 
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