Whats the difference in the 4.0 and the 4.0 high output engine in the jeep Cherokee?

Answer 1

87-90 is the 4.0 with the RENIX (Renault/Bendix) fuel injection system. This is considered the "low output" motor.

91-06 is the 4.0 High Output with the Chrysler fuel injection system. Cherokees 91-96 and Wranglers 91-95 were badged as "4.0L, High Output".

The main difference between the two is the head flow characteristics. The ports in the head for the intake/exhaust are bigger and flow more freely, along with a change in camshafts and the deletion of some sensors, such as the knock sensor found on the RENIX 4.0s. The throttle bodies are also different between the two, intake manifold changes did not come about until 1999 and exhaust manifold changes did not come about until 2000, when Chrysler also switched to the coil on plug ignition system.

Personally, I believe the exhaust manifolds on the later 4.0s(2000-2006) are of a much better, 2 piece design. I say this because they do not have the tendency to crack much like the manifolds of earlier years. Unfortunately, this also brought on the addition of 4 oxygen sensors and two pre-cats in the exhaust stream of many 4.0s produced in this time period.