Well I know the cliche is that we don't buy these for fuel economy, but I did. Diesel was the key to me purchasing a Jeep years ago and of course I liked Jeeps and the TJ hit my price range for a vehicle that was in good shape with a general structure that was as high tech as I wanted. Since the 1940's diesel really has been the king engine cycle and fuel for doing work.
Diesel has a bunch of benefits over gasoline and yes negatives as well, but the negatives are generally monetary related. Over long periods of time or mileage the negatives tend to diminish for diesel engines. In any case for my build and desires the diesel benefits far outweighed the gas options, though there were certainly some heavy contenders, but the main contenders were already something I could buy off a lot any day in the US. Also when civilians aren't allowed to buy something but government vehicles are allowed as well as buyers from third world countries, then the contrarian in me solidified around a diesel build.
I guess I need to address that the measuring stick won't really work if you compare buying a used vehicle and only repairing it vs converting something from an OEM to a diesel or any other engine not designed to be there. If you want reliable, which typically beats efficient, with cheap repairs, just rebuild your Jeep pretty similarly to OEM and don't go buy a new one. New ones are great, but at the end of the day a POS used vehicle that's over a decade old or more will be cheaper. Well the older 3.8 may have something to say about that, but that's another discussion. OEMs just have resources we don't. They can take multiple over qualified engineers to run analysis and physical testing on a single bracket and then take it to a team of engineers to figure out how to make it as cheaply as possible, thinking about it every way imaginable.
Because of the access in the US, the measuring stick will be a personal one. I used roughly a price of a new Jeep and used the taxes and insurance cost as well and assumed the upgrade would be similar to the upgrade price for Cherokee for the EcoDiesel. Truly this is flawed, but typically we all seem to like to compare. I guess the reality is that it is what I would buy if it was offered and the newer shiny stuff with some awesome entertainment stuff really does very little for me. The incredible comfortable rides, make me want to sleep while driving as well. Even a manual makes me have to think more when I'm driving, though as much as it pains me, I can't knock that hard on autos anymore.
Anyway doing basic calculations and from real world driving I knew I needed around 300 ft-lbs of torque. HP isn't something really needed, but it's a little bit important for deciding on your transmission, but really a torque curve is what you need and once you know RPM and torque you're good to go. If you race then HP matters a lot, but there's no way I'd pick a Jeep to race.
Down time was another big factor for this build. I love driving my Jeep. It's still a bit wild and untamed. So I didn't want to buy a spare Jeep and I didn't want to be working on this project for years and I wanted to plan when I pulled my 4.0 before it blew up on me. At this moment the R2.8 has a lot going on for it. I don't have to search classifieds or junkyards and research stuff heavily just to order the wrong stuff that I can't return. I read Cummins literature, talked with Bruiser and Axis Industries. Axis was closer and seemed to have most of my favorite builds, they worked with Cummins on their Jeeps and they sold a kit (though it went off their site right after I ordered it), so I put the money to the side ordered everything. And if some parts weren't delayed and life didn't delay me, could have been driving in weeks rather than just a couple of months. My Gobi rack will take longer to acquire than it takes to do this swap.
It wasn't incredibly simple, like swapping the 4.0 out for a 4.0, but it's doable for most people. I had been really wanting to do a big build for years and at the moment that want does feel fulfilled and I'm still not done. Now that I'm driving and I was working well over 12 hr days almost every day I could throw at it and staying up relatively late, for me, after work to get more done, I'm finding that I really needed a break and for a bit I'm going to not work on this at all and it's functioning perfectly well in any case.
