Upon first acquiring our 4.0L-equipped '01 Jeep Wrangler TJ, we were extremely impressed with its on- and off-road performance. The six-cylinder mill pushed the stock-size tires anywhere we wanted to go, with plenty of power to spare. As the buildup ensued, however, big tires, big axles, and more gross vehicle weight than the engine wanted to push slowed down the once mighty rig. We initially addressed the issue with the installation of an AEM Brute Force Air Intake System, and a Banks TorqueTube Exhaust Manifold Assembly and Stinger Exhaust System. Combined, the free-flowing intake and exhaust systems greatly benefited the stock 4.0L by creating a better breathing engine and offering impressive horsepower and torque increases. As we continued to build the TJ, however, bigger tires again came into play, as did the removal of the AEM heat shield to make way for an engine-driven air compressor. Not willing to the see our power numbers drop, we decided it was high time we went straight to the top. We wanted to talk to the brain of the operation: the TJ's ECM.
Fluent in vehicle computer-ese, Doug Farrell of Doug's Brea Auto Electric in Brea, California, operates a full-service automotive repair shop specializing in computer reprogramming and fuel-injection upgrades. Doug confirmed our suspicions that the 4.0L I-6 engine had more power capabilities than the vehicle's ECM allowed it to produce. With so many limitations put on vehicle manufacturers concerning fuel conservation and emissions, the ECM is programmed to create the most efficient running engine in all respects. Horsepower and torque loss is usually the result, as the best of both worlds commonly translates to better fuel economy and less power. So where does that extra horsepower and torque disappear to? Essentially, it lives in the ECM just waiting to get out. The power is there; the computer just has to tell the engine to produce it. Once reprogrammed, it can do just that.
In reprogramming, or "flashing," the vehicle's ECM, Doug is able to address all aspects of how the vehicle performs rather than just specific points such as a replacement chip might. Transmission shift points, throttle position, timing, boost, load, and many other facets of the engine and related components can be adjusted from within to aptly suit the way the vehicle may be set up. Doug began the reprogramming process by developing a build sheet of the vehicle, with detailed information regarding tire size, gear ratio, engine modifications, and primary type of driving. The computer can then be programmed to perform however you want it to, providing more or less top end, midrange, or low-end, all within the parameters of how your Jeep TJ is built and used.
One area we didn't pay much concern to in the computer reprogram was fuel mileage. Although the ECM can be flashed to achieve greater fuel efficiency, saving dollars during our commute wasn't our ultimate goal; power and torque increases were. As a result, we lost around 2-3 miles to the gallon, which is a small price to pay for a more responsive vehicle.
Concerning emissions, Doug informed us that a typical smog station won't detect any changes to the vehicle, providing it's not out of spec or doesn't meet your state's smog requirements. If you make a trip to the dealership, however, you'll need to instruct the technician not to flash your computer with factory updates, or you'll lose the reprogram altogether. For those of you worried about Doug's ability to properly carry out such a process, rest assured that he has a professional on the job. The same guy who performs Doug's reprograms writes Mopar Performance ECM programs, as well as a full line of GM Performance and OEM programs. Many auto manufacturers also use his services for their aftermarket and racing activities.
Although the dyno results revealed increased horsepower and torque numbers, we didn't necessarily feel that they reflected how beneficial the ECM reprogram was to our Jeep TJ. An increase in torque was the most substantial gain, and it's extremely apparent when behind the wheel, whether we're on the road or the trail. Throttle response in low-speed situations is phenomenal, allowing us to charge tricky obstacles with a good degree of wheel speed when 'crawling isn't an option. On the highway, we're able to maintain 75 mph at 3,200 rpm with enough left under the pedal to quickly hop up to 85 or 90 mph while still under 3,500 rpm. A Corvette even threw down a challenge after following us onto the highway and witnessing how rapidly we brought the TJ up to speed. We didn't accept the offer, but it was nice to know we're deemed worthy of a duel, especially considering the Dana 60 axles and 37-inch tires. Despite the loss in miles to the gallon, the Brea Auto Electric ECM reprogram certainly proved to be a valuable upgrade in creating the greatest degree of power from seemingly nowhere.