My 88 has probably topped 300K by now - and I'm finally getting rid of the damned Peugeot transmission (been through four...) and I need to change out the engine management sensors. Engine still pulls strong and clean - and will do better once I get the sensors all changed out.
Weak points?
- Lack of aftermarket support (especially for 1987-1990)
- Cylinder head is relatively restrictive to airflow
- Failing engine mounts can cause exhaust manifold cracks (there should be a flex joint between the manifold collector and the downpipe.)
- Low-mounted alternator can be a problem with mud and water.
- Vacuum-actuated front axle disconnect (1991-down, or thereabouts. You've got it, if you've got the NP231 transfer case with no full-time 4WD option.)
- Early XJ's (1995 and earlier) are a bit under-braked - swap in a 1996-up dual diaphragm brake booster and associated master cylinder. Also, if you have ABS, plan on removing it.
- 1987-1990 control electronics aren't available in anything else
Upsides?
- Built by AMC - "All Makes Compatible." Most engine management parts are standard GM for the era
- The AW4 automatic is rock solid. If you have the five-speed, it's the Peugeot - change it soon! However, the automatic is just great
- While it's not a "wind-up and go" engine like in most other vehicles, the 4.0L will give you 90% or more of peak torque from ~1300-3500RPM. Ideal cruise is around 2800-3000rpm, which it can do all day long.
- 1987-1990 control electronics very rarely fail (see above)
A high volume oil pump isn't necessary, and can cause trouble for you anyhow. I wouldn't worry about getting ARP fasteners unless you're overhauling the engine already anyhow - but there's no need to "just on account of 'cause" at 180Kmiles, assuming it's been treated well up to now. Even then, the AMC six is fairly tolerant of abuse, and so are the AMC chassis (I once pulled an 18K# load with my 1987. Didn't go fast, but I got it where it needed to go - from Morgan Hill to San Jose. I'm not sure I'd want to do it again, but it did it the first time. Why did I do it? The boss had the shop truck, and I needed to get that project going.)
Check your rear axle carefully - it could be either the Dana 35 (oval cover) or the Dana 44 (irregular hexagonal cover, "resting on a point.") The Dana 44 was a fairly rare option, and 1988 was the last year for it (domestically - it was available a bit longer in export vehicles,) but it's a damned solid axle and you'll want to keep it.
If you have any more specific questions, I'd be happy to help you. However, that's all that leaps readily to mind with an open-ended question like that...