Which brings me to the vehicle’s problems. While the AMC-derived “High Output” (by early 90s standards) 4.0L inline 6 and associated Aisin-Warner AW4 are a notoriously bulletproof combination, this Jeep has traveled enough miles to circumnavigate the Earth 10 times. Many of those 240,000 miles have been questionably maintained before I got it, and life hasn’t been easy for it since. Since this is California, and Chrysler’s electrical engineers wired it, every other year’s required smog check is a game of Russian Roulette hoping our trusty steed doesn’t throw a code while being inspected. While the AMC engineers who designed the original I6 architecture went with maximum Soviet overkill on the mechanicals of the engine, Chrysler’s electrical engineers went with “we’re sending this shit to the moon” levels of wire weight savings. 18AWG is ubiquitous. 120A alternator? 12AWG got this. Starter? Schmaaaaaybe 4AWG. Strain relief is hilariously non-existent, nothing is supported and thermodynamics apparently doesn’t apply since regular plastic loom protects wiring mere inches from the non-heatshielded tubular exhaust manifold.This harness connector isn’t important or anything: it only houses the key-on wiring to the ECM’s relays which you can hear clicking away with every movement. Really awesome experiencing this herky-jerk engine on-engine off-engine on-engine off action on the freeway and even more fun to diagnose. How you see it is exactly how Chrysler designed it: vertical orientation for maximum water intrusion and zero support.
One of the biggest problems with the HO 4.0 I6 is heat. This damned thing runs hot, all the time. Even with a larger radiator, nearly locked fan clutch, external coolers for power steering and transmission fluid and hood vents to help evacuate heat, the all-iron construction, hilariously poor BSFC (11-13mpg for a 4000lb, 190hp vehicle), small nose blocked by a winch, 100lb wheel/tire combination, armor and brick-like aerodynamics conspire to make for a vehicle that requires constant coolant temp surveillance. The reverse-flow cylinder head takes all of this heat and cooks the many sensors on the intake manifold to a nice crispy consistency. The wiring to engine management sensors was designed as what I can only believe was a practical joke: poor insulation, encapsulated trays running the entire length of the head near the exhaust manifold, and pitiful wire gauge. Currently, my Jeep’s main sensor harness above the intake/exhaust manifolds is one-piece: all of the plastic insulation has melted together. This makes any repairs to this wiring a complete end to end replacement.