Jeep XJ LS Swap: What is it, What does it do and How to do

Due to the LS engine’s quality and ability to improve the function of almost any car that receives the modification, the world of custom cars has undergone a significant transformation since GM introduced it in 1997. 

These small, lightweight, durable engines are worthwhile investments for car owners looking to revamp their aged cars with more power, better air intake, high performance, and longevity. LS swaps for older Jeep XJs are logical in the same sense. 

While you can still feel a sense of concern when you consider how little can be altered about its old-fashioned build, Jeep XJ LS swap is pretty much a possibility, provided you know what you’re doing. Here’s some insight into how to do this successfully.

The LS Swap: What Is It and What Does It Do?

An LS swap means swapping your existing engine for any model from GM’s LS series. The most popularly swapped are the LS3 and the sixth-generation Corvette-based LS7 engines. LS swaps are generally carried out on older cars and trucks with worn-out or underpowered engines by today’s standards.

Created in 1997, the small block engines are still in production today. In almost every LS lineup, you’ll find high-performance engines capable of generating more than 300 horsepower, mainly due to their classic pushrod technology. 

The LS engine’s intake manifold features a technology designed to deliver decent power up to high RPMs while producing usable power low in the RPMs. It’s even possible to make over 440 rwhp with just head work and a cam on an LS engine. And their extensive use in motorsports is undoubtedly a testament to their efficiency and excellence.

The variety and abundance of LS engines have made them the most popular swap engine for hobbyists. While these engines are highly customizable, they’re also cheap, as are the related labor costs, and the job takes a skilled technician only a couple of hours to complete.

How to Do an LS Swap on a Jeep XJ

Transplanting an LS motor under an XJ is reasonably straightforward, so long you’re aware of what to consider and how to deal with the process accordingly. Here’s everything you need to know.

What XJ Models Are Suitable for LS Swapping?

If you’re worrying thinking whether your aged XJ can handle the swap or not, that’s pretty much understandable. 

But rest assured: you can perform the swap on any XJ, even if it is a model before the 2000s. 

In particular, if you use the LS V8, you can bring any XJ up to modern power standards. On post-1995 models, you can easily reprogram the computers with the swapped engine, while you can easily deal with older, hard-to-program models by purchasing a separate engine control unit (ECU).

What Are the Requirements for the LS Swap?

If your Jeep XJ is going to undergo a total overhaul, the LS engine is bound to be the centerpiece, but it needs a few friends to work with your machine. You should invest in ten things regardless of whether you upgrade to an LS V8 or anything else from the LS line. They are: 

  1. Motor mounts
  2. Accessory drive
  3. Intake manifold
  4. Exhaust/Header
  5. Power adder
  6. ECM/Wiring harness
  7. Transmission
  8. Transmission Crossmember
  9. Setting tools
  10. Dress items (preferably Motorsport speed cover)

Following is how all these elements are combined for a Jeep XJ LS swap.

Steps to Follow when Swapping LS on a Jeep XJ

Undoubtedly, the first step is to obtain the LS engine for your XJ. And who knows, you might just find a dirt-cheap one in a junkyard. You can still purchase blocks-short or long-for a relatively small price even if you choose to buy one from a vendor. But how should you begin your swapping? Let’s see.

Step-1: Mounting

First and foremost, when installing a replacement engine, you need to consider the mounts, which will hold it. Luckily, many companies today offer LS swap kits for everything from F-body sports cars to Mazda Miatas.

Take the TransDapt Swap-in-a-Box kit, for instance. The kit contains everything necessary to install an LS across the fenders of your Jeep XJ. In addition to headers, oil pick-up tubes, oil pans, and engine frame mounts, the kit includes transmission mounts and crossmembers for nearly any GM-made gearbox.

Other than TransDapt, you can find LS swap kits compatible with virtually any combination you want. And once you have installed the engine and transmission, you’ll need to consider the exhaust system.

Step-2: Configuring the Exhaust

Finding a set of custom headers for any swap used to be problematic in the past. Nowadays, however, there is probably a pre-built set sitting around and waiting for your swap. 

For example, some brands like Hooker already have pipe sets that clear the engine bay of any Jeep XJ. They have headers available for your old Cherokee, as well as multiple coatings, turning what was once a hassle into a breeze. There’ll be nothing to worry about the configuration once you get one aligning with your particular XJ.

Step-3: Fitting Transmission and Torque Converter

Regarding these parts, many people wonder if old-school TH350 or 400 transmissions would fit on an LS. Well, of course, it would. 

Despite the differences in the bolt patterns, you can directly attach older Turbo transmissions to an LS engine without an adapter. However, it’s a different story with a torque converter.

A few different torque converter options for a Jeep XJ LS swap are available. The spacing and mounting locations of the torque converter can be adjusted using a custom torque converter, or you can use a spacer for your swap.

The spacer simplifies the installation by moving the flexplate towards the transmission to fit correctly into the torque converter. You should place the torque converter no closer than 1/2 inch from the engine in most cases. You risk misaligning the converter with the input shaft and trans pump if you go any further.

The spacer fixes this geometry by coupling the crankshaft flange and the flexplate so that no custom parts are required. It’s also by far the simplest solution.

Step-4: Keeping Your LS Cool

Next, you must ensure your transplanted LS remains cool underneath. Some people think they can just use their stock radiator and find conversion hoses, but this isn’t always possible. 

An all-in-one radiator kit from Be Cool is one sure-fire way of ensuring that not only does your LS have the proper routing but that it can also cool as many horses as you intend to build. You can also expect a much cleaner installation as the kit includes pre-molded hoses, a fan, and a protective shroud.

Step-5: Adjusting the Throttle Body Control and Gauges

How do you use a cable-operated throttle body on a vehicle that doesn’t already have one? It’s a common question regarding the LS swap on a Jeep XJ. The solutions to this issue are numerous, but some are easier to implement than others.

Consider running a drive-by-wire throttle body engine (Gen IV and up, as well as Gen III). In that case, buying a pedal position sensor and mounting it is the easiest solution. While it’s easy to install, it also helps clean the engine bay. 

Another option is to re-flash the PCM with an OS (operating system) that initially came with a drive-by-cable throttle body. Typically you can only accomplish this using Gen III engines installed on both sides of an XJ. An ECM must have a driver for the idle air control valve to operate it, which most Gen IV controllers lack.

It’s always best to stay with whatever your vehicle has by default. It doesn’t make sense to overcomplicate it by swapping the controller operating systems since both routes are pretty straightforward.

Be sure to check all the functional gauges as well. You’ll need to replace most stock gauges with those from a GM-based Corvette or pickup truck. Junkyards are good places to buy parts like these.

Step-6: Wiring and Configuring the Computer

Wiring is arguably the most challenging part of the LS swap, whether it’s on an XJ or any other vehicle. These days, electronics are far more sophisticated than ever, adding complexity to any modern mill you might be swapping into your ride.

Luckily, however, manufacturers like Holley have gone to considerable lengths to make the process of swapping an LS as simple as plug-and-play. When using their stand-alone wiring harnesses, you won’t need extensive wiring knowledge to install an LS.

The wiring harnesses for LS swaps are available in three variants: standalone, custom, or rewired from the original harness. The third option is most popular due to its cost-effectiveness and ease of completion by a professional. 

Wiring-wise, MSD’s Atomic EFI kit includes everything you need for an LS swap with all of the fuel rail connectors, plugs, and controllers built-in. The tuning system is simple, requiring only the input of a few parameters via a handheld device, without any extensive knowledge of tuning.

Additionally, if you don’t want to run EFI, you can get carburetor kits from MSD rather than port fuel injection. It ensures that you can still keep that old-school appearance while retaining a modern coil-near-plug ignition, thus providing the best of both worlds.

Step-7: Optimizing the Fuel System

For Jeep XJ LS swap, you must keep a constant fuel pressure of 58 psi. You can accomplish this in several ways. The easiest is to add an aftermarket in-line fuel pump. In addition, you can obtain custom tanks fitted with modern fuel tank sender assemblies built to fit your needs.

Step-8: Tuning the Air Intake

You must consider the air intake, the final step in the XJ LS swap. Several vendors sell air intake kits for the LS swap on Jeep XJ, or you can choose a universal kit.

It’s essential to consider whether you will use the mass airflow sensor or a speed density tune for the car. You can place pretty much any filter on the throttle body if you choose to go with the speed density setup, or you can just use a straight pipe with an attached filter.

In contrast, if you are keeping the MAF, it might be a good idea to use a universal air intake kit like those from Spectre. Having a built-in MAF slot, such a kit can keep the installation looking clean.

Thoughts

As mentioned earlier, a Jeep XJ LS swap is a much simpler process than any other engine swap. You can buy any part that you’ll need to complete your swap without the need to fabricate from one or more vendors, including everything from the intake to the pickup tubes.

And last but not least, make sure you take all necessary safety precautions to avoid potential hazards. Do the work in a well-ventilated area and keep any flammable items away from there.

Related Posts: