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Hey all, I'm fairly new to the forum. Been lurkin a while :peek: finally decided to make an account since I bought a 'manche! Thing is, it has a gutless, 2.8 with a bad rod. I'm buying a parts xj this week, and am going to be swapping out the 2.8 for a 4.0, an AX5 for an AW4, and the dash cluster (I hate idiot lights). Wanted to ask to see what I need to change for the swap, anything i might have to buy or fabricate myself for the swap, and see if anyone on here could offer any advice for the swap, maybe tell me things I need to know or consider while doing it? Any and all help is much appreciated!

-Matt

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Hello neighbor :waving:

 

A lot of small questions will depend on what years the trucks are. Obviously, being a 2.8, your MJ is an 86. Any year XJ will work, all with about the same amount of work to get it...working. Your MJ is literally going to have to be gutted, and replaced with everything from the XJ. This means all the wiring. Also, IIRC, the 2.8 used a mechanical fuel pump, so you're going to need to find a sender for your tank.

 

You're also going to need a new rear driveshaft, but since your current shaft is longer than you need, it's easy enough to have it shortened. (I'm assuming they are both either 2wd or 4wd).

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MJ's have a foot more wheelbase over an XJ so rear shafts do not interchange.

 

nothing in your MJ will help the 4.0 to function. it ALL needs to be swapped, including the radiator and rad support (which necessitates swapping the hood and latches too). it's been done. :thumbsup: oh, and you'll need to splice the XJs rear lighting wires into the MJ harness and the aforementioned fuel pump and whatever changes to the lines it might need.

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The 4.0 rad will not fit unless doing some cutting to the head light buckets, modifying the upper rad support and lowering the frame rails some. You will also run into clearance issues with the header panel if you put it right under the upper rad support.

 

The other thing you will have issues with is the firewall. The firewall was changed in '87 to be pushed back slightly and was flattened out so the 4.0L would fit. You would need to get a BFG and add some love to the firewall to get everything to clearance correctly.

 

To give an idea on the radiator, here's a pic I took while doing my build.

 

 

This is an image of it with the new rad bolted in (crappy picture but only one I really have of the new rad bolted in place).

 

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As I understand it there are issues with the firewall too. It needs to be modified to fit a 4.0L. There is another option for you which is replacing your 2.8L block and heads with a Camaro(?) 60 degree 3.4L. All the ancillaries from the 2.8L will swap to the 3.4L. No firewall, wiring or radiator mods.

Please correct if I'm wrong, just repeating info I read here before :wrench:

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Been there, done that :ack: If you wish i can snap some pictures of mine and how i made it work, but it will have to wait untill this weekend. Its in a million pieces and parked in my parents garage.

 

Pics are always great! And I've heard the same about the firewall, but when i measured its exactly the same as a friends '93 XJ?

 

-Matt

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As I understand it there are issues with the firewall too. It needs to be modified to fit a 4.0L. There is another option for you which is replacing your 2.8L block and heads with a Camaro(?) 60 degree 3.4L. All the ancillaries from the 2.8L will swap to the 3.4L. No firewall, wiring or radiator mods.

Please correct if I'm wrong, just repeating info I read here before :wrench:

I've heard the same thing. This is the route I would go if I had an '86. The GM 3.4 is a very reliable, simple, and cheap replacement for a 2.8 (which isn't really all that bad to begin with.) You can probably even keep your oe intake/exhaust.

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The 3.4 is a great swap if you just need a refresh. More power and a bit more reliablity.

 

Now don't take this the wrong way because I absolutely love the 4.0, but if I were going to all the trouble to make it fit an 86, I'd go ahead and step up to a v8. A good small block ford, chebby or mopar will give you more power. (but I'm a power junkie).

 

But that's just me.

 

I understand cooling can be a factor with a V8 in a comanche, but it can be done. As much work as it is likely to take to do the 4.0, that's what I would do.

 

If the 2.5 in the TJ ever gives up the ghost, I think it will be due for a v8. Problem is the dang thing is so reliable that it just keeps going. 175K and still popping.

 

Good luck with whatever you decide.

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I was thinking about swapping in a 3.4, but from what ive read/heard the ax5 is gutless, and won't hold up as long as i'd like. But on a side note, when i swap in the i6, i was planning on swapping in the xj's axles, but the comanches rear is spring under, and the xj's is spring over, and i was wondering if anyone could give me an estimate of how much lift that will put in the back so i can decide what to do with the front to level it out.

-Matt

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Some fabrication is also required to get the XJ rear axle under the MJ. The spring perches are at a different width as well as the shock mounts being different. It might look close, and it will go in, but you'll tear up spring bushings in a hurry.

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