Swap a 4.0L in for your 258
Bolting it all in the Jeep
Here is where all the fun begins. You get to take out all kinds of junk from under mine. I think there was about 8 billion miles of vacuum hose under my hood. If you have an early YJ with a 258 the motor bolts right in. Mine bolted right to my motor mounts and transmission. (I have upgraded to an AX15 and tossed my stock Peugeot).
Your transmission bellhousing will need a location to mount the crank position sensor. (The AX15 already has this mount). I have a friend that did this swap into a CJ-8 that had a 258. The engine bolted right to his motor mounts also.
If you have a 4 cyl. Jeep you will have to cut off your old motor mounts and weld in new ones. You will need to find a location for your new computer and under-hood fuse box. I mounted the computer on the firewall where the newer Wranglers have theirs. The under hood fuse box was mounted to the side of the battery tray. The easiest way to do this is just to get a battery tray from a newer Jeep. I had the benefit of a fab shop to make my own mount.
Wiring the Beast!
Ok, I will be honest. This part scared my to death before I began the project. There are a million wires and it can look very confusing. It is really very simple. When it was all said and done I really only used about six wires from the Cherokee harness. I went to the local Jeep dealer and got a picture of the bulkhead connectors for the Cherokee that the engine came from and for my 87 Wrangler. This way I could mesh the Cherokee harness into my Jeep. (Tip: the color codes in the Chilton's manual I have are completely wrong).
Most of the wires that run into the bulkhead connector are specific to your Jeep and can be left alone. I pulled out one wire at a time from my original harness and got rid of the ones that were specific to the old motor i.e. old computer.
The only wires that you will need to splice are ignition, and any sensors for your gauges. Everything else should be specific to your Jeep and you do not have to mess with it. Basically you just plug the new harness into the motor; the plugs will only go on one way. Supply power to the new fuse block. It should have the battery cables attached to it. Make sure you have a good ground and sensor ground. I know this sounds pretty basic and it is really that simple.
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