Eagle

^^^ This. The early (Renix) XJ and MJs sometimes had a problem with a weak signal from the CPS to the ECU due to the fact that the CPS fed through the wiring harness to get to the ECU. The factory released a fix that bypassed the wiring harness, using a new connector that went directly through a new hole drilled in the firewall and straight into the ECU. For an 89 or a 90, the original CPU connector wires should go into the big wiring harness. If the CPU connector has two wires that run directly through the firewall, that vehicle has had the bypass performed.

I have to disagree. Mounting the anchors for the shoulder straps will be a real problem in an MJ cab, but the practicality of using a 4-point harness on the street is nowhere near as bad as you make it out to be. For several years, when I was campaigning a Javelin in Autocross, time trials and hillclimbs, I ran a Simpson 5-point harness in the car. I used all five when racing and skipped the anti-submarine belt when driving it on the street. It wasn't at all uncomfortable, and it wasn't at all inconvenient. Tightening the straps doesn't require help. The tabs fall within easy reach. Once adjusted, you know they are adjusted. There's no wondering if the retractor is going to fail when you need it to grab. But ... I had a roll bar to attach the shoulder belts to, so I had the correct angle. I don't know where you could anchor them in an MJ other than bolting through the rear wall of the cab just below the window.

If he can shift it manually, the transmission obviously works. The problem is either the fuse for the TCU, or the TCU itself.

Zinc chromate kills rust? I know it has been used as a primer for many, many years, but I have NEVER heard that it kills existing rust. Got a link to some documentation on that?

Can't be done with the stock Jeep wheels because there are no retainers to hold the moon caps in place.

If the thermostat was stuck open I doubt very much there would be normal heat coming out of the heat vents.

Is the school's truck 2WD or 4WD? If it's 4WD, you could replace the 3.08 axle with 3.55 and it'll drive a lot better. If it's 4WD, of course the rear axle has to be the same ratio as the front. As noted, Cherokee axles are the same except for the location of the spring perches. I'm pretty sure I have a 3.08 axle buried under the snow outside. Once the snow melts, if you haven't found anything I could send you the gears if your instructor has the skills to set up a differential.

ECU? I thought the fuel pump relay was triggered by the fuel pressure regulator. What year MJ are we talking about, anyway?

Welcome. If we don't have answers for you ... answers probably can't be found. Some of our answers may even be correct. We don't even charge extra for those.

The ratio for the manual steering is ridiculous -- something like 24:1 or 28:1 ... compared to 14:1 for the power steering. I haven't had manual steering in an XJ or MJ but I remember the factory manual steering from my Javelin days. The ratio on that was 20:1 and it was horrible. Not too heavy (I changed all mine to the 16:1 quick ratio manual boxes for autocrossing), but much too slow. With the XJ/MJ manual boxes being even slower -- I can't even imagine how horrible it would be to drive one. Don't even want to think about it.

I'm going to guess control arm. When bad they make a very noticeable clunk, and because they are a steel sleeve inside a rubber bushing they always have some play anyway ... so it's difficult to diagnose them visually.

Factory spec is zero camber -- dialing in camber is the worst thing you can possibly do for a street vehicle, unless you have lots of money and REALLY enjoy buying tires.

Get a TruTrac. It's a gear-actuated limited slip. More aggressive than the clutch-type Trac-Lok, but still street friendly for daily driving.

They can do the alignment, they just want to sell him parts. My brother used to be service manager for a BMW dealership. One of his biggest problems was doing battle with certain of the technicians. When a car would come in for service, instead of getting to work fixing whatever the complaint was, their priority was always to waste a bunch of time going over the car to see whatever they could find to "upsell" more parts and labor. I view it as an evil aspect of the auto service trade. Virtually all shops today pay technicians and service writers a percentage of whatever parts and services they can sell, so there's a big incentive to sell parts that aren't needed. The worst part is, when you decline the unneeded parts, there's a high probability the tech will get pee-oohed and do a crap job on the work that DOES need to be done.

They ALL leaked -- right from the factory. I bought my '88 XJ new, and the operable vents were an extra-cost option that I paid to get. They leaked right from the day of delivery. The factory had a cure -- they offered to replace the operable windows that I had paid extra for with the standard, non-operable windows. (Naturally, they weren't going to refund the cost of the option from my purchase price.) If you plan to use the vents, plan on their leaking. There is NO way to stop it. I sealed the ones on my XJ with silicone and I haven't opened them for more than 20 years. Fortunately, none of my MJs have operable vents.

The shape of the track bar and the drag link don't matter. What counts is the angle of a straight line drawn from the upper pivot point of each to the lower pivot point.

Geonovast is correct, the AMC pony cars used a Model 20 rear axle behind the V8s and the hubs were splined onto the axle shafts, not forged as one piece. It wasn't difficult to spin a hub off an axle -- I managed to do it, with a 2-barrel 290 c.i.d. engine. The ratios weren't great, either. The standard ratio was 3.15:1 with the 4-speed (3.54 optional), and 2.87:1 with the automatic (3.15 optional).

What extra gear? The 242 doesn't offer an additional ratio -- the full-time 4x4 position is still high range, 1:1 ratio, just like the part-time high range. The full-time position is something that's useful in street driving, when pavement conditions may alternate between slippery and dry frequently. It offers no advantages that I can think of for off-road.

IMHO ... no. They don't need it. As Alexia posted above, if you drop the pitman arm without dropping the track bar mount by the same distance, you screw up the suspension geometry and you will have bump steer.

The moly? Yes, it helped, but on very cold mornings I still bypass the 1-2 shift and just go to the first downhill from my driveway in first, then jump directly to third.

With the XJ/MJ inverted Y steering, the draglink IS the right side tie rod end. If you look at the parts listings on Auto Zone and other sites, I don't think you'll find a "draglink" (or "drag link"). You'll find left and right side, inner and outer tie rod ends. It can be confusing when the tie rod "end" is more than two feet long. My '88 MJ had a 4" lift when I bought it. No dropped pitman arm, and the stock drag link was plenty long enough.

I use 75W90 GL3 gear oil with a liquid molybdenum disulphide additive I used to buy from JC Whitney. Dunno if JCW still sells it (I still have one bottle left) but more recently I've seen a company on the Internet called Mr. Moly (or something like that) that sells what appears to be the same stuff.

Not really limited slip, although they did use clutches for locking. In operation the Quadra-Drive diffs functioned exactly opposite to a clutch-type limited slip like a Trac-Lok. In a Trac-Lok, which most of us here are familiar with, the clutches are normally engaged. If one wheel loses traction, the clutches allow the axle to transmit torque/power to the opposite wheel -- up to a point. If the amount of power/torque exceeds the gripping force of the clutches, they release and the diff functions as an open axle. This is what allows the diff to be "transparent" to the driver when turning corners on dry pavement. In the original Quadra-Drive, the diffs are normally UNlocked. When one wheel begins to rotate faster than the other wheel on the same axle, the valve in the internal gerotor pump begins to open, sending hydraulic pressure to the clutches and progressively engaging the locking function of the differential. Since the Quadra-Drive system was always in full-time 4WD (the only option was to shift into low range), this was always working. It was quite aggressive, and under some conditions it was obviously operating on dry pavement. Usually, though, it was "fairly" transparent on the street. Engagement off road and in slippery conditions was very aggressive. The original Quadra-Drive system was completely mechanical-hydraulic. There were no sensors involved, and no computers. I know the Quadra-Drive II is different (which is why it's called Quadra-Drive II). I've never read anything that fully explained why Jeep changed the entire system after just a couple of years, but I know that "VNH" (vibration, noise & harshness) was a big concern in the Grand Cherokees, so my best guess is that the original Quadra-Drive's occasional lack of "transparency" wasn't acceptable to the NVH engineers. Too bad, because that part of the '99 WJ was great. The rest of the vehicle, however, was pretty much junk.

From the book manuscript I started several years ago (permission to reproduce is NOT granted): To answer your question, to use the '90 brakes on the '88 axle would also require replacing the calipers and steering knuckles.

That's the Quadra-Drive II. The '99 WJ used no computers. I know how Quadra-Drive worked, and I know what an automatic locker is. I understand that mnkyboy doesn't want a locker with a 242, but his explanation of why he thinks it's bad is utter nonsense. A lot of people also spout similar alarmist BS about how terrible even a limited slip is in snow. I'll be 69 years old in a month. I've been driving since I was 12, legally since I was 16, and except for a year in Maryland and a year in Vietnam courtesy of the U.S. Army, I've always lived in New England. I've been driving vehicles with limited slips or lockers since 1966, and if I had my druthers I'd never own a vehicle that didn't have at least a Trac-Lok. You guys do what you want, but stop spreading disinformation to support your own phobias.