Wrangler engine swap questions

[Eagle]

I good friend across town has a '99 Wrangler 4-cylinder that needs an engine. His step-son gave him a '99 Wrangler 4.0L. About the only solid items left on that one are the removable hardtop, and the engine. So the plan, which we started to implement tonight, is to swap the 4.0L into the TJ with the solid (mostly) body and frame.

 

Question: How much of the wiring harness does he need to pull from the donor vehicle? We know he needs the engine harness and ECU, but he said he has read (on the Internet, that fount of infallible wisdom) that he also need to change the body harness. That doesn't sound right to me, but I don't know much about Wranglers.

 

Haw anyone done this swap? What's involved?

 

(Yes, we know he needs new frame brackets for the motor mounts.)

[Pete M]

I speak from complete ignorance about the state of TJ electrical systems, but there's no way I wouldn't just swap it all.  why risk it?

[jdog]

In not sure about the body harness, but if the new one has a programed key,  all the components must match for the vehicle to start

[Eagle]

Both TJs are 1999. No programmed keys.

 

[FrankTheDog]

Unplug the old engine harness and plug the 6 cyl harness in and see if it works. If it doesn’t, change the body harness too. The ax15 may have different connections than the ax5 and the wiring length may not work either. The tach will probably be off if you don’t change that out.

[kryptronic]

You should be able to plug the 4.0L engine wiring harness into the existing body harness without issues.  Jeep tried to make all that stuff as interchangeable as possible.

 

For example, in the previous generation (YJ) during the 1991-1995 high output years, the only difference between the 4.0L and 2.5L engine harnesses were wires for two injectors (whuch could be spliced in), and a power steering sensor (used on the 2.5L only to increase idle when turning the wheel when stopped).

 

So your chances of that 99 TJ harness just plugging in and working tight are really good.