more Mopar Part 1 - stock 2.5 Removed - Photo 36785721

Back to Article

The factory 2.5L and AX-5 powertrain had served us well over the years and was still in working order when we plucked it from the Wrangler. Though we suggest holding on to your stock parts until the V-8 swap is complete, selling our engine and transmission combo helped offset a good portion of our conversion cost.

Since our donor engine did not come with a power steering pump, we used this opportunity to upgrade to a hydraulic-assist steering system from PSC Motorsports. And while it is not recommended to run the stock V-8 pump with the factory steering gear box, it can be done by having a set of custom hoses made.

To achieve a little more elbow room we removed the entire front clip from the TJ. This may seem like a lot of work, but it’s actually pretty easy and will save you a ton of aggravation and time later on.

The scariest part of most engine conversions is the dreaded electronics. We decided to make life easy on ourselves and leave the cutting and splicing to the experts. This required that we send both the donor vehicle’s V-8 harness and factory 2.5L harness along with the fuse block to Hotwire Auto. Be sure to let the company know if you’ll be converting to an automatic transmission from a manual, as this will require an extra fuse and insert. We’ll show more on how Hotwire Auto makes engine electronics a plug-and-play affair in Part Two.

The factory 2.5L and AX-5 powertrain had served us well over the years and was still in working order when we plucked it from the Wrangler. Though we suggest holding on to your stock parts until the V-8 swap is complete, selling our engine and transmission combo helped offset a good portion of our conversion cost.

One part that is not required for the V-8 conversion but is strongly recommended is a 1-inch body lift. We installed a 1-inch kit from Daystar so we could tuck the new powertrain as high into the tub as possible. The mild body lift also made more space for routing the exhaust.

Our 5.9L from the ’99 Dodge Durango came with most everything we needed, with the exception of a few pieces of smog equipment. Be sure to spend as much time as you can rummaging junkyards for any assorted pieces (like smog equipment) that are missing. These items are very pricy at the dealer, and a few minutes in the field digging can save you a lot of change.

To secure the engine in place we bolted on a set of Advance Adapters Chrysler V-8 engine mounts to the block. On the frame side we cut off the factory mounts and welded on the other portion of the Advance Adapters kit. Be sure to keep the hardware loose, as it will make alignment of the transmission mount and assorted linkage much easier.

The 5.9L cooling inlet and outlet ports are positioned opposite as compared to the factory four-cylinder. To accommodate this change and increase the cooling area, we went with an Advance Adapters Jeep V-8 radiator that’s designed to bolt in place in a TJ.

Though the Advance Adapters unit can be used as equipped, we had our local radiator shop weld on a larger-diameter lower inlet so we could run a factory lower hose from a 5.9L ’99 Dodge Durango. The upper hose came from the same Durango, but it needed to be trimmed down a few inches.

To finish out the cooling equation we used a fan from a ’98 5.9L Jeep Grand Cherokee and a radiator shroud from a ’99 4.0L Jeep Wrangler. The junkyard is a great spot to pick up both parts, but since both items are relatively low cost, you’ll be OK grabbing them from a dealership if you have to.

Since our 5.9L isn’t running any extreme power adders the factory four-cylinder fuel pump will work just fine to feed the engine. Though dropping the tank is not required for the conversion, it’s not a bad idea to test the output pressure of your old pump and buy a new one if it’s low.

Our Jeep was equipped with the AX-5 manual mated to an NP231 transfer case with a 21-spline input gear. Moving up to the 46RE Dodge transmission required us to swap out the factory T-case input with a 23-spline unit from Advance Adapters.

One thing we had terrible luck with was the factory Dodge V-8 computer. After going through a couple of junkyard ECUs (engine control units) and having no luck getting the truck running, we ordered a factory replacement unit from Auto Computer Exchange. The company builds the computers to spec and requires an ECM core. We suggest trying your donor computer at first, but Auto Computer Exchange is a reputable backup plan for when things just won’t compute.