Best 4.0 engine year for replacement

Well, you start by violating Federal Law. The Federal EPA regs about engine swaps say that only the same model year or later engine may be fitted to a smog-controlled vehicle. Practically this means that if you live in a state that does emission testing, you will fail the test and continue to fail. Therefore you will not be able to legally transfer title to anybody else in that state, since passing smog is required at sale. Thus you can only legally make this mod on an "offroad only" vehicle without plates, not driven on the road. And you own the vehicle until it gets scrapped.

Having said that, I once put 150,000 miles on a 4.0L HO engine in a 1992 XJ. I never had any internal engine failures, just an idler pulley and a couple of water pumps, which are bolt-on external parts. But it was still an OBD 1 engine with electronic ignition and electronic fuel injection, but with a high voltage only distributor, and timed off the flywheel sensor. But there are aftermarket carbureted manifolds and real distributors for that model year.

A 1992 with cam, free-flowing carbureted intake, and headers would put a smile on your face IMHO. But I don't know anything about the transmission compatibility, I had a 3-speed auto.

toecutter1978 said:

Ok thanks I guess I should stay with the oldest year I can get. Anybody think there would be an issue with the 42RLE transmission bolting up to a 2000 4.0?

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There shouldn't be any problem bolting up. Controlling the 42RLE with the 2000 era controls is another issue. BTW, the 2000 on up have distributorless ignition, which is very nice, 1999 and older have distributors with rotor/cap/wires to worry about.

It might be best for you to get an older long block and keep the current controls, if it's the string of 4.0L camshaft issues that has you worried. Actually, only a few people have had the camshaft issues, so unless you have a problem, you should just keep what you have.

The 4.0L I6 has the same bolt pattern throughout it's manufacturing run, same as the 4.2L before it. In fact, the AMC V8's used the same bolt pattern.

If you really want to get rid of the electronics, you're going to have to change the transmission (not the transfer case though). The 42RLE is electronically controlled and needs the engine controls to work properly (I haven't heard of an aftermarket / standalone control for it.) So you could go to a 4.0L from a 1992-1996 XJ with the XJ's AW4 automatic, and it will bolt up to your current transfer case.

For a V8 swap, you'd have to change the transmission anyway, so there are a lot of different options. The Hemi with 5 speed automatic from a 2003-2005 Dodge Ram (non-MDS) is a popular swap, and the electronics are compatible with the 2003-2006 Wrangler instrument cluster. There are a few kits available to take care of the engine mounts and wiring as well (AEV and Summit both offer them). Unfortunately, since they didn't offer a non-MDS hemi in 2006, there isn't any model-year legal swap available for 2006 owners.

There are also controls available for the GM V8 swaps, to adapt the stock instrument panel.

At 91K miles, you are going to replace some stuff. At around 93K on mine, I replaced almost every electronic sensor, coil packs...etc. I do have to agree with you, the newer motors are a lot more finnicky than the 99 and older motors. That being said, I would do some quick math and calculate cost vs. rewards.

-Like others have stated, you are messing with the emissions on a vehicle. Being in Fort Hood, are you in the military? If so, thanks for serving, and you will not stay there forever if you plan on enlisting longer. Say you come to CO, we don't emission test vehicles in Colorado Springs except diesels. What if you end up in CA?
-97 4.0 motor for 500.00 (get the wiring harness and PCM)...and we will just say it is a good motor that doesn't need anything like a rebuild...for now.
-AW4 trans for 300.00 (get the TCM and harness)...and we shall say that is good too.
-Most likely you will have to do some skid plate mods, drive shafts etc...unless they are all the same length transmissions.
-Now you will need to get your dash to work. Go find a old gauge cluster to fit into your dash. you may be able to get yours to work..but doubt it.
-Exhaust mods...they are similar...but you will still need to run the cat and O2 sensor.

-Now lets say you don't get a great motor....and you rebuild it on the cheap for 700.00
-We will say the same for the transmission, but I know better. It will cost way more than that. 700.00

So have you had 2200.00 worth of problems on your 06? This is just the very low estimated costs. No fab time, no supplies, no labor unless you are going to do this all yourself. Most anything in the emissions control you can replace easily or with a little effort.

To me, it sounds like you are heading for a nightmare. I have seen this from V-8 swaps in "whatever" by people getting cheap and not getting a new wiring harness from someplace like Howell for 900.00 and spend the next 6 months in the garage trying to get a vehicle to run instead of hooking up 4 wires and turning a key on. Some people are very successful and do a great job, and don't mind spending the long hours in the garage. I was the same way, not anymore. I would rather wheel.

toecutter1978 said:

Thanks for the response. Your welcome, I enjoy serving. I do plan on retiring here, around in Texas. I just want to simplify my rig. I don't have cool electronic gadgets wired into my Jeep because I believe if it can't get wet and dirty it doesn't belong in it. The few electric add on I have are just a few lights ran by relays. I really enjoy my rig and I think my problem is I try to fix things before they are issues, like on the trail.

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Start with a CJ or YJ chassis and you'll be thousands of dollars ahead. The TJ was the first digital Jeep even though it doesn't look like it. Just look at the number of things in Chapter 8 of your FSM that end in the words "Control Module". Your drive to replace all of the microprocessors and digital circuitry will require you to replace most of the powertrain (you can keep the axles and driveshafts once you get the lockers under full manual control), all of the vehicle wiring harness, and then you will end up with a collection of barely functional work-arounds for not having the various digital gimmicks. NOBODY makes a kit for what you desire because it would cost more than having a complete spare Jeep. Even if you succeed it will only be after the afore-mentioned years of frustration over a non-running "hanger queen" that was formerly a working Jeep.

I do know a couple of people who tried to do what you describe. One of those folks last wheeled with me two years ago - as a spotter - and the other parted out the dead carcass of a formerly nice TJ.

Considering the number of '97 TJs I see on the trail, it is also wasted effort. All the digital circuitry resulted in Jeeps that run better and last longer than the older models.