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Old 10-30-2017, 09:15 AM
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Join Date: Oct 2017
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1988 Sahara Engine Swap Questions


I'm new to the forum but I've been reading forum builds, projects and tech questions on here as a guest for quite some time now. Now that I'm investing into a new Jeep I immediately thought of wrangler forum as the place to go! I used to have an '88 Wagoneer but I sold it after a ski accident. I've been Jeep-less for a few years now and I have to say, it's been pretty awful!
I'm about to head up the coast here to purchase a 1988 Wrangler Sahara. It has the 4.2 carb'd engine in it but the engine is blow and needs replaced. It's also got the Pukey BA10/5 transmission in it that is still running (surprise!) but I'd like to replace with a much sturdier transmission.

My question is this -
Can I pull a 4.0 engine, an AX15 and mount those directly into the jeep without cutting new motor mounts and other components? Are there better options to swap than a fuel injected 4.0 with an AX/15 behind it?

I'll admit, I've wanted to drop a diesel engine into a YJ for quite some time as well and this seems like a great opportunity to do so. Especially if I'll have to change the motor mounts anyways to accommodate for a 4.0.

I'd like to transition to F/I since I regularly run from sea level to high elevation. And I'd like to see how feasible it is to keep this swap under $3,000 for a gasser or $6,000 for a 4bt/merc swap.

I just moved to Florida from Colorado here so most of my equipment is still back in the mountains. If anyone in South Florida is looking for something to wrench on, some packs of beer and pizza, I'd be more than happy to oblige to keep me out of the shop labor prices!

Thanks folks! Looking forward to seeing some great ideas.

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Old 11-04-2017, 10:22 AM   #2

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Depending on what the donor vehicle costs, I think you should be able to keep the costs from running over $3K.

You might be able to find a Cherokee with a standard transmission. Most of them were auto, but I've seen a couple sticks. Buy the entire vehicle so that you'll have everything necessary to use the FI. A cheap rusted out XJ might be common in Florida.

A 4.0 in place of a 4.2 is a common swap and won't require changing motor mounts. It will require "clocking" the transfer case to fit under the YJ tub, but it's not too difficult.

You'll need a Factory Service Manual for the YJ and the XJ so that you can match up whatever wires are necessary to make the Jeep run. You'll need to use the sending units from the YJ to make the gauges work.
You'll also need some kind of electric fuel pump. A 1991 or newer YJ FP/sending unit is the simplest way.
The BA10 uses a mechanical speedo and the Cherokee will have an electronic speedo and speedo drive. You can use the Cherokee speedo drive and a '91 and newer YJ speedo head. Use the two FSMs to figure out how to wire the electronic speedo.

The mechanical part of the 4.0 in place of a 4.2 swap is relatively easy. Converting the carbureted engine bay to fuel injection requires a ton of patience and a whole lot of planning. If I were planning such a swap, I'd search this and other forums for information and look into UTUBE for vids.

Good Luck, L.M.

"Wrangler....It's not just a vehicle, It's a lifestyle".
.................................................. ........................
1987 YJ-4.2L-Standard Shift- Re-manufactured Carter Carb-2" body Lift-31X10.5X15 BFG KOs-190K Miles No back seat.
HEI distributor with computer and all related relays and wiring removed.
12K Badlands winch with dual batteries.
Warn front bumper. Matching imitation Warn bumper on the rear.
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Old 11-09-2017, 11:51 AM   #3
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I agree with most of what Luckymac had to say, however the best scenario you could find would be another YJ with the 4.0 in it. Finding a dirt cheap XJ might be easier, but YJ's after 89 came with the 4.0. You could keep your original T-case so the connection to the speedo will not change or you could install the newer t-case. If you install the newer t-case you will need to find a guage cluster out of a newer YJ for everything to work.
87 YJ, 5.7/TH350/NP241, Custom 4 link/ Radius Arms, ADS Nitrogen Shocks, 35" Cooper STT
DaddyJeep build Thread:https://www.wranglerforum.com/f8/dad...ld-122601.html
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Old 03-14-2018, 04:02 PM
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Thanks for the responses! I think I've decided to just swap the 4.2 and put an AX15 behind it just for simplicity sake. I think doing a TBI conversion later on will fit my needs better, once I've got the funds and everything ready and in place. Now it's time to look into swapping the BA10/5 for an AX-15!
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Old 03-15-2018, 08:45 PM   #5
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A couple things you should be aware of swapping the trans, although the bellhousing bolts to the 4.2 block things change quickly. The trans mount on the BA10/5 differs from the AX-15. This can be fixed a few ways, 1, swap out the skid plate if you have a donor YJ, 2, after market adapter (about $50) 3, if you have the AX-15 mount bracket, it can be modified to accept an urethane mount. I did #3.

The other big hurdle is the NP231 transfer case. The output shafts on the two transmissions are different 21 vs 23 splines, you can replace the planetary gear in the transfer case if you can find a good used one, they're not to expensive. But beware at some point NP changed the cut on the gears. The planetary gear and the gear in the front of the case fit together but I'm not to sure how strong it will be. So if you find a used planetary try and get the front cover also.

Do some research so you know what your in for and good luck.
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Old 03-24-2018, 09:07 AM   #6
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Great thread, I'm planning on doing the same thing

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