The 4.0L Jeep reference, sourced.

Verified fixes, specs and part numbers for the 4.0L straight-six Jeeps: XJ, MJ, ZJ, TJ and YJ. Every spec and part number links to where it came from, and every page says which years it covers: 1987–90 Renix, 1991–95 HO, or 1996–2001 OBD-II.

Browse by system

Engine (4.0L & 2.5L)
The AMC 242 4.0L inline-six: Renix, HO and OBD-II versions, head, seals, oil and belts.
Fuel & ignition
Crankshaft position sensor, TPS, IAC, fuel pump, heat soak and ignition.
Cooling
Overheating, thermostat, radiator, fan clutch, water pump and heater core.
Diagnose a problem
Step-by-step flowcharts: crank-no-start, stalling, rough idle.
Transmission
AW4 automatic, AX15, BA10/5 and NV3550 manuals.
Transfer case
NP231 Command-Trac and NP242 Selec-Trac.
Axles
Dana 30 front; Dana 35, Chrysler 8.25 and Dana 44 rear.
Electrical
Gauges, speedometer, grounds and relays.
Body & rust
Cowl leaks, floor pans, rockers and unibody repair.
Steering & suspension
Death wobble, steering box, caster and leaf springs.
Specs
Fluid capacities and torque tables, sourced and year-split.
Buyer's guide
Years to avoid, common problems and an inspection checklist.

How this site works

We cite factory service data, service bulletins, NHTSA records and parts catalogs. Where sources disagree we show the conflict rather than pick a number. Each page shows its last-verified date. Read the editorial & sourcing policy.