Eagle

1990 was the first year for the second generation of the XJ/MJ front brake system. The knuckles, rotors and calipers are ALL different from previous years, IIRC. I don't know if the pads might be the same, but if the calipers are different I rather doubt it. Here's the Cliff's Notes capsule summary of what fits: The above is copyrighted and may NOT be reproduced or distributed. You may print out one copy for your own, personal use.

Take yours out and inspect it. If the rubber spacer is intact but has collapsed (compressed) vertically, just put it back in and shim it with a couple or three washers on each bolt. Bottom line, though -- if it hasn't collapsed far enough that the exhaust pipe is resting on the cross member, it probably hasn't collapsed enough to be causing any problems.

You said you can't drive a standard. If it has 3.07 gears, it's a 5-speed. What you're looking for is an XJ with a 4.0L and the AW4 automatic. That's a 4-speed automatic -- 3 speeds plus overdrive. Although the Dana 44 axle would be good to have. But you'll still be looking for a tranny.

What a surprise!

Good. I hope he's either rich or has plenty of insurance. Just remember -- when the accident is the other guy's fault, there ain't no such thing as a "total." You drive an irreplaceable truck because that's what you choose to drive. You are legally entitled to have your truck repaired to the condition it was in before the accident, using all factory parts (which is a laugh, since they aren't available, but it'll keep them jumping), plus having a rental ride while yours is being worked on. Don't let anybody stonewall you. If the clown doesn't have insurance -- put a lien on his house.

The short answer is -- because you can die. The medical treatise is a bit more lengthy and technical, but that's the bottom line.

Correction -- Snore well!

Idler pulley? Water pump? Alternator? Power steering pump?

CPS. That's the culprit when a good running truck suddenly won't start, in probably 98.75% of the cases.

It's not impossible -- it will be a bolt-in swap, but you'll be changing all the underhood wiring, and you'll have to find a gas tank that's set up to work with the V6 mechanical fuel pump. The big things is, the 2.8L won't get out of its own way any faster than the 2.5L. Personally, I'd prefer the 2.5L over the V6 any day. The 2.8L V6 was badly under-powered in the Chevy S10, and it was badly underpowered in the Jeep Comanche. If you look at the actual torque and horsepower ratings, you'll be doing a LOT of work for effectively zero gain.

If you plan to ditch the rear height-sensing valve, you MUST remove one of the two lines from the front. Specifically, you keep the one out of the "nose" of the front metering block, and you remove the one coming out of the bottom of the metering block and plug that outlet. This has been written up in several different threads on here. I know it's impolite to greet a new guy with "Try using SEARCH," but I don't have any of those threads bookmarked because I already know what needs to be done and how to do it. So rather than me search it for you, I'll simply recommend that you search it out. It's here, along with a lot of other useful info about MJ brakes.

If it has enough fuel pressure to start, the fuel pump works. It sounds like the ballast resistor. Simple test -- hot wire the fuel pump and see if it will run more than 30 seconds.

yeah its a crap motor. worst motor ever from GM... to my knowledge Your (lack of) age is showing, Grasshopper. GM actually did have an even worse V6 engine. I don't remember the displacement, but it was introduced in the original Buick Skylark back in the early 1960s. And, in a clear demonstration that those who do not learn from the mistakes of history are doomed to repeat them, GM sold THAT engine to Jeep, too. My brother had a CJ-5 back around 1972 that had that engine in it.

Well, this puts me in mind of two of my favorite sayings: The first, I have no idea where I heard it. "People who think they know everything are particularly annoying to those of us who do." (Best said in the inimitable voice of Jim Backus -- the millionaire from "Gilligan's Island") The second is from none other than Lucy Van Pelt, of "Peanuts" fame: "I'm perfect. I thought I made a mistake once ... but I was wrong." (Yeah, think about it. It'll come to ya!)

I concur. 150 degrees is well below the temperatire at which the ECU switches to closed-loop operation. I think it's around 165 to 175 degrees.

Yes, you could take it to the bare block. That means "block," not "block + head." To use your manifolds, you will need to use your head (or another non-HO head). To use the '98 HO manifolds, you'll need to adapt a bunch of brackets for things like the alternator and power steering pump. And you'll have to adapt your throttle body to the newer intake manifold. You will also have to tap a hole to mount the knock sensor in the block, because the HO engine doesn't use one. Dimensionally, the '98' block is the same as the '90 and will fit the chassis with no problems. But, as the saying goes, "The devil is in the details." You will find that you'll be doing a lot of adapting. It is not going to be a drop-in replacement. It all comes down to how cheap you can buy the '98 engine, how creative you are about adapting ... and how much time you can tolerate the truck not running while you figure out the conversion.

^^^ What he said, exactly. This isn't a "Jeep thing." Carburetor icing is what happens to airplanes flying at high altitude in winter. I have never heard of a carburetor heater for an automobile, and I'm old enough to go back to when chokes "knew" when to open up by a coil spring in a can, not by an electric heater element. I've owned several cars with manual chokes. I have never, EVER encountered "icing" of a carburetor in an automobile. Remember that the function of the thermostst in a car is to keep the temperature UP, not down. Some genius may have put a low-temperature thermostat in your MJ, or even removed the thermostat entirely, thinking it was a good idea. It isn't. Your first step should be to buy the correct thermostat for your engine and install it.

All your stuff? No. Many of the brackets for alternator, power steering pump, etc, are totally different between the 1990 Renix models and the 1998 Chrysler models. The ports on the head are different, so you can't (easily) swap your manifolds onto the "new" engine. The throttle body is different. The injectors are different. The flywheel is different and won't work with your CPS, but if you try to use the 1998 CPS ... it won't work with your Renix computer. Even the oil filter is different.

28-inch, actually. A 215/75R15 is 27.7" in diameter, and a 225/75R15 is 28.3" in diameter. I hooked JeepCO up with a spreadsheet that calculates RPMs and road speeds for all the available gear ratios and for tire sizes from 205/75 up through (IIRC) 33", so he's been doing his homework.

Pat is probably pretty well dialed-in with that setup. For anyone else contemplating gears and tires, I'll pass along my frame of reference: the original vehicles this engine family was designed for. I used to have, back when I was in the Army, a 1966 Rambler American. It had the original, 1-bbl carbureted version of what many years later developed into the 4.0L engine. I don't remember the tire size, but they weren't huge. My American had a 3-speed manual tranny (no overdrive), and 3.08 gears. One of the first things I did was buy a factory tachometer kit for it and install it, so I know (and still remember) the speed-to-RPM relationship. 24 MPH per 1,000 RPM. Which worked out to 60 MPH being exactly 2500 RPM. 3000 RPM got me a 72 MPH cruise, and it would run at 3000 RPM all day. With all the overdrive transmissions and such we have today, there's a tendency to think that anything over 2000 RPM is going to "burn up" the engine. Not so. I sold my American short of hitting 100,000 miles, but my brother had a '72 Gremlin with the same setup that went at least 308,000 miles with NO work inside the engine. I say "at least" because he sold it to one of the local parts stores and they used it to deliver parts. We lost track of it after 308,000 miles, but it was still going strong at that point. Back to my Rambler American -- cruising at 60 MPH/2500 RPM, I reliably pulled down 28 miles per gallon highway. The point of all this is -- don't be afraid to put in a bit more gear than what came from the factory. The factory chose the ratios to try to score well on the gummint's very artificial fuel mileage and emissions tests, not for what would be best for actually driving the vehicles in real life. On stock tires, my '88 5-speed turns about 1650 RPM at 65 MPH on the highway. That's well BELOW the torque peak of the engine, which is not optimal for anything.

Running at the same temperature (or wanting to) is not the issue. The issue is that a SBC generates more heat than a 4.0L, and has less space around it in the engine room to allow some of the heat to dissipate. I've only seen a few SBCs stuffed into Cherokees, but they ALL had cooling issues -- even the one with a custom aluminum radiator that was supposedly "guaranteed" to do the job. The '91 and newer "open" radiators (the ones with a neck for a radiator cap) have provision for an overflow bottle.

No photos. It's been years since I did one, but I have mounted a Kenwood, a Pioneer and a Panasonic in various XJs and MJs. My recollection is that each came with a mounting sleeve/bracket that fit into the dash, and then the radio slid into the bracket. IIRC, two of the three fit with no alterations to the factory dash bezel, and one of them (the Kenwood?) required filing the opening about 1/16" on one side to allow it to fit over the radio faceplate.

DOT 3 and DOT 4 is glycol-based. I don't think that's a veggie oil, but I'm not a chemist, so I don't know. It is physically impossible to "mix" silicone brake fluid with glycol-based brake fluid. The operative word for mixing two fluids is "miscible," and the two types ain't miscible. It's like pouring oil into a glass of water. Shake it up enough and you'll get globules of oil dispersed throughout the water, but they aren't "mixed" and, if you let it settle, eventually the oil all floats to the top in a separate layer. Same with DOT 5 and the glycol brake fluids. There is no chemical reaction. You can fill a small container partially with DOT 3 and/or DOT 4 and then pour some DOT 5 into the glass. Nothing will happen. Come back after letting it sit for an hour, and it'll be completely stratified. But, any time there's glycol fluid in the system, that fluid is hygroscopic (attracts and holds moisture vapor), and one of the primary reasons for using silicone is that it is NOT hygroscopic. So combining (I won't say "mixing") the two in the same system defeats the purpose of spending the extra money for the silicone.

On a related note, I was thinking before the "It turns!" report that the bearing journals might have developed a touch of surface rust that was causing them to stick to the bearings. I think I'd want to inspect them all and maybe even give each journal a quick polish with crocus cloth. Then brew up a mix of 15W50 or 20W50 motor oil mixed about 50:50 with STP, "Motor Honey," or one of the really thick viscosity index improvers, and coat the journals and bearings with that before reassembling.

Maybe not. That may be why the factory switched to motor oil. I wish someone would figure out if that new Pennzoil Synchromesh lube would work in the AX-15 and AX-5 trannies. I called Pennzoil when it first came out, and their engineer told me that lube was formulated for the NVG 3500/3550 and 4500 series transmissions. He didn't know what would happen if you used it in an AX-15 and he didn't care to speculate (at least, not to a customer -- wise man). I rather suspect it would work just fine, but I don't have a spare AX-15 to throw under the bus as a test specimen just in case it doesn't work just fine. Has anyone tried the stuff?