The 4.0L Jeep Wrangler engine
had a fantastic horsepower compared to it's predecessors and peers. The 6-cylinder Jeep Wrangler engine offered excellent acceleration and torque for an engine of it's size. The engine was engineered by American Motors Corporation (AMC), and was based on the Typhoon Six which was introduced in 1964. The 4.0L Jeep Wrangler engine featured a shallow-skirt cast-iron block with uniformly spread out cylinder bores, a seven-main-bearing crankshaft, loop-flow combustion chambers, and in-line valves. The 6 cylinder engine boasted 180 horsepower when placed in a Wrangler, and 190 horsepower when placed in a Jeep Cherokee.
Beginning in 1991, the Jeep Wrangler engine used Chrysler engine processors, allowing for stress-free diagnostics. Between 1996 and 1998 changes were made to subdue sound, shaking, and harshness from the 4.0l Jeep Wrangler engines, together with a different cam lobe profile to cut valve seating speed, isolated valve cover fastenings, and adding a main bearing brace.
The 4.0L Jeep Wrangler Engine performed well, with few caveats. There were a few problems with the basic design, including sparatic leaks; the oil pump was infamous for wearing out at around 140,000 to 160,000 miles, and the TPS (throttle position sensor) on the '89 and '90 models was inadequate at best. Be sure to have around 30 pounds oil pressure at idle (give or take 5 lbs). The main reason for abandoning the 4.0l Jeep Wrangler engine was the oldness of the engineering parts. The pressurized coolant surge tank generally developed pin-head leaks, and there are alternatives which will work better at cooling.
The engine also can develop deterioration as a result of the cooling system. The original Renix injectors have an inclination to leak. If you suspect or detect a leak, it would be a good idea to replace your injectors with Five-O Motorsports' Jeep injectors. If you experience oil leakage from the rear of the engine, the o-rings that seal the oil filter mount have most likely deteriorated. They are Nitrile which have short life spans. Substituting the o-rings with 70 Durometer Viton rubber resolves the problem.
When AMC decided they wanted to better their engine line, they made a decision to abandon the 4l altogether. To entirely retool would have been almost as expensive as upgrading the 3.7 liter engine did, and time is money. Rather than being pragmatic, money reigned supreme as they were told to, "Make a modern engine, and junk the old ones." Since then, engines have become progressively more efficient and a new 4.7l long block engine was released, a powerful upgrade for the 4.0L Jeep Wrangler Engine. The engine ups the ante to somewhere near 265 hp to 290 lb.-ft of torque, and is designed to fit Jeeps fitted with the 4.0L Jeep Wrangler Engine from 1991 to 2006.
About: A 2003 4.0l Jeep Wrangler with a manual transmission gets an average of 18 miles to the gallon on the highway, 15 mpg in the city. The same jeep could accelerate from 0 mph to 60 mph in 10 seconds and can reach a top speed of 108 mph. Considering that the 2003 jeep commander engine
weighs over 2 tons, those are pretty good times!