Through these chapters, the Jeep will be transformed into the ideal Jeep defined above. Lift kit, larger tires, lockers, new wheels, bumpers, and much more will be added with details along the way.
The Jeep featured in this book is a 2004 TJ Wrangler Unlimited in completely bone stock and ready for a transformation. A stock Jeep is an excellent starting point in a used Jeep intended as a project. Finding one is often the bigger challenge. This Jeep will find itself with a new look and will be ready for a new life upon completion.
CHAPTER 2
FACTORY ENGINES AND ENGINE SWAPS
It’s commonplace for owners of classic Jeeps such as AMC-era CJs (1972–1986) and earlier to swap engines because of the low-performance engine options in those years. In addition, swapping a tired old engine in a Jeep that’s 30 or more years old is quite simple thanks to simple computer controls or even a lack of computer controls altogether. These engines often have simple emissions controls and may be exempt from emissions inspections.
In the past, swapping a small-block Chevy into an older Jeep such as an AMC-era CJ was common, easy, and relatively inexpensive. The modern TJ presents some complexity with a swap because emissions requirements are stiffer now. A swap with an engine of the same year or newer will often satisfy emissions requirements. (Photo Courtesy Ben Mann)
Engine swapping is much less common with the TJ. It’s only recently that changing engines has become more popular because of the TJ’s age. In many parts of the United States, vehicles are required to pass emissions testing that can present a challenge to the Jeep owner who hasn’t thought the swap through. In this chapter, I will explore swapping engines in greater detail and provide some guidelines to help with planning.
Factory Engines
Only three engines were offered with the TJ series: two different 4-cylinder models and one 6-cylinder. All were good engines. Unlike the series before the TJ, all of the engines offered used modern multi-port fuel injection (MPFI) that improved reliability and performance. The end of the Wrangler TJ series also marked the last use of the AMC engine, the 4.0L, which was replaced with the Chrysler 3.8L and 3.6L Pentastar V-6 of the JK series.
The Power Control Module
Perhaps before jumping into engines, discussing the Power Control Module (PCM) might be prudent. As modern vehicles evolved, the introduction and development of computerized systems increased their presence to the point that almost all of a vehicle’s systems are controlled or monitored by the PCM. If you have had the pleasure of owning a CJ, you may understand the simple nature of its computer-less system; it’s easy to troubleshoot and diagnose problems. While the complexity of the newer systems can seem daunting, these systems allow components, especially the engine, to produce more power while maintaining efficiency and clean operation. The PCM in the TJ years is mounted on the passenger’s side of the firewall in the engine compartment. It operates, monitors, and adjusts most of the engine functions, including spark timing, air-fuel ratio, idle speed, and much more.
The Chrysler Pentastar V-6 is the latest engine found in the JK Wrangler. The 3.6L has a smaller displacement than the 4.0L but thanks to modern technology, such as variable valve timing and dual overhead cams, this small engine puts out an impressive 285 hp, a big jump over the 190 hp of the 4.0L.
The power control module (PCM) controls and monitors almost all of the engine operations, making the engine more efficient and producing optimum power output. These modules are easily replaced in the event of a failure even though they are extremely reliable. The factory attempts to find a balance of performance versus efficiency. This allows the aftermarket to make add-ons to the PCM to improve performance.
2.5L MPFI 4
The 2.5L is an AMC-built engine introduced in 1984 that was designed specifically for use in Jeep and Eagle vehicles. It shared some components and specs from the I-6; however, it is not a “cut down” version of the I-6. The version of the 2.5L used in the 1997–2002 TJ was an MPFI design and was labeled as the Power-Tech I-4. The engine produces 121 hp at 5,250 rpm and 139 ft-lbs of torque at 3,250 rpm. Even with its small horsepower and torque ratings, with the correct gearing and low range this engine will keep a Jeep moving on the trail without issue.
2.4L DHOC 4
The 16-valve 2.4L replaced the 2.5 in 2002 and continued until 2005. Running dual overhead cams and four valves per cylinder allowed the engine to produce 147 hp at 5,200 rpm and 165 ft-lbs of torque at 4,000 rpm. This engine (in a number of variations) was used in many Chrysler vehicles until it was discontinued completely in 2005, when Chrysler’s World Engine replaced it. Like the 2.5L, this small engine is capable of keeping a Jeep moving with the proper gears.
Both of the 4-cylinder engines perform as well as they can, which is very limiting in a TJ. The small-displacement engine struggles on the highway when larger tires are added to the Jeep and the gears aren’t addressed to correct the effective ratio. The underpowered engines really perform their best off-road when using the Jeep’s low range.
2.5L and 2.4L Performance Upgrades
Many argue that there isn’t much more to be pulled from the 2.5L or 2.4L without spending more than a 4.0L swap would cost. Many Jeep owners have reported that most upgrades available do not make the difference that justifies the expense. Often it is reported, in an unscientific way by Jeep owners, that the improvement in performance seems to diminish as the Jeep’s engine controls work to control fuel input/exhaust output effectively. They conclude that as the engine adjusts it eliminates any gains. The investment is not worth the gain.
Several companies make performance mufflers for the Jeep that are often part of a cat-back system. This one from Banks is on a 4-cylinder TJ; its free-flowing design adds a little horsepower and some added engine tone. The cost of these systems is often not worth the minimal gain. However, if the system is in need of a replacement, it might be a worthwhile replacement. Most cat-back systems are stainless steel for long life.
Performance computer chips offer improvements in varying conditions by adjusting spark timing and air/fuel ratio. Installation is simple and can be done in less than 30 minutes. Chips from Jet and Superchips are available in varying forms and stages for TJs of all years. These modules typically install at the PCM and are placed inline with one of the PCM’s plugs.
Clean, Less Restricted Air: A new or, even better, reusable-style air filter alone can improve engine performance. These filters allow increased airflow and improve throttle response as well as fuel mileage. K&N filters are possibly the most popular reusable, high-flow filters available.
Exhaust: PaceSetter makes a direct replacement header for the 2.5L and 2.4L that provides increased exhaust flow that results in performance improvement. In addition to the header, a few companies such as Banks make cat-back systems that improve exhaust from the catalytic converter to exhaust exit.
Computer Modules and Programmers: Adding a modified computer