Eagle

"In My Not So Humble Opinion"

ANYBODY makes a better filter than Fram. As to why you have to convert to the horizontal filter mount, it's because the vertical mount uses a metric thread, and the oversize filter(s) you want to use don't come in the metric thread. If you have a '92, you already have the horizontal mount so that won't be an issue for you. Personally, I can't think of a single good reason for making the conversion. If you use decent oil and a decent filter, and change the oil at a sane interval, the normal size filter is plenty adequate.

The stock cat is 2-1/2" but the stock system from the cat back, including the muffler, is 2-1/4". Yes, the larger exhaust is hurting your mileage. The first replacement exhaust on my '88 Cherokee was a 2-1/2" cat-back with a Walker turbo muffler. I lost about 2 or 3 MPG and I could definitely feel the loss of low-end torque. It was the first time in my life I was actually hoping for an exhaust system to rust out, and that I celebrated when it was time to replace it. I went back to the stock size and I've been much happier.

Gawd, I don't remember. It's been a couple or three years since the last time I bought them. I just walked into Advanced Auto and ordered them. Whatever they gave me is what I used.

That vacuum cannister is what stores vacuum for the HVAC controls. If you have factory cruise control, it has a second chamber for the cruise. It is used on the HOs as well as the Renix, so "upgrading" to an HO engine won't eliminate it. The engine itself doesn't need it; it's not part of the engine controls. You have to be careful about stuff you hear. There are a lot of people out there who will happily tell you they know everything about Jeeps, and in reality they don't know the headlights from the taillights.

Run a compression check. Severe overheating can take the temper out of the piston rings. The engine will run after that, but it'll be down on compression, down on power, and always burn oil. Don't ask me how I know this ...

I may have mis-read the deal. Are you getting complete axle assemblies, or are you getting the differentials, gears, and axle shafts only? If all you're getting is the internals, then UNLIMTD is entirely correct. In fact, setting up used gears is MORE difficult than setting up new gears, because if you don't hit the original engagement pattern pretty much spot-on you'll always have noisy gears. So on top of the $225 for these parts, you're looking at maybe $75 for the Trac-Lok clutch kit, new pinion, carrier and axle bearings, and new seals. And a new crush sleeve for the pinion preload. Plus paying someone to do the install. Gotta be honest -- unless you do some hard-core wheeling, you don't really need the front True Trac. Rather than toss all that money at used stuff, if I were in your situation (which I was when I bought the '88 MJ) I would just buy a new True Trac for the rear D35 and pay someone to install it.

Be sure to use the new (95 and up) oil pan gasket. It's WAAAY easier with the new one-piece gasket than the old three-piece set that you had to glue together at the corners with RTV. If the NAPA listing doesn't show the new one as a supercede for the old style -- ignore the listing and buy the pan gasket for a 95.

I know some guys who do it themselves. I don't. The "gotcha" is that you have to have the pinion depth and the backlash set perfectly so the gear mesh pattern is correct, or you get noise and rapid wear. The "right" way to do it is to use a fancy gauge set to measure the pinion depth. I can't afford that tool. The shade tree method is to use white marking compound and "read" the gear engagement pattern, then adjust as necessary. That's what my friends do. My mentor is a long-time stock car racer, shop foreman, and later service manager for the AMC/Jeep dealership where I used to buy all my cars (until new owners booted my friend because they wanted to bring in one of their cronies as service manager). He did all my gear work. Once he didn't have access to the shop's gear setting gauges he refused to touch gears because he felt is was too much of a chance to mess up and expensive set of gears. So my position is, if Joe won't touch it ... I ain't gonna touch it. But the reality is, it ain't rocket science. If you're careful and you're willing to learn how to "read" the gears, I'm sure you can do it. Best approach would be to degrease, mark, and read the old gears before you take anything apart. That'll show you what they should look like. Then you just aim to duplicate that pattern.

Both the True Trac and the Trac-Lok are limited slip units, not lockers. The difference is that the Trac-Lok (which was the factory option) is a clutch-type limited slip. It WILL wear out over time (for me, the original in my '88 Cherokee lasted about 150,000 miles), and it requires a special additive to the differential lube for proper operation. The True Trac is a gear-operated limited slip. It doesn't wear out, it doesn't require special additives, and once engaged it's a bit more aggressive than the Trac-Lok. It also cost about $100 more. You mention towing. You should NOT tow with a locker. Period. If towing is part of your plans, go with a limited slip. The units you're buying will be very adequate for the use you describe. BUT ... $225 is barely the cost of a new Trac-Lok alone. If you're getting both for $225, they're used. I would not install a used Trac-Lok without replacing the clutch packs, and that's another $75 or so just for parts. Also, both these units are full differentials, so be sure they are the correct units for use with your gear ratio. I don't recall offhand where the carrier breaks are, but I have a feeling that one or the other of your axles has a carrier break going from 3.07 to 3.55, so if these came out of an automatic, one of them may not be suitable for your vehicle.

My '88 XJ 4.0L 5-speed is stock with 3.07 gears. I get around 21 to 23 MPG highway. My '88 MJ 4.0L 5-speed has been swapped to 3.73 gears and I am currently running stock tires on it. Highway mileage is typically 19 to 21 MPG, with the tailgate up and no tonneau cover. The 3.07 gears actually leave the 5-speeds cruising well below the engine's torque peak at legal highway speeds, which is not ideal for efficiency/economy. 3.55s or even 3.73s will put you closer to the "fat" part of the torque curve at highway speeds, and that's really where you want to be running.

I don't think the FSM specifies a pressure. Never saw one. If the system is operating properly, it shouldn't matter. The normal operating temperature is 210 degrees, which is below the boiling point for unamended water at sea level. With either the second or the current (third) radiator in my XJ with the closed system, the temperature with a 195 degree t-stat never goes over 200. Ditto the '88 MJ, with the original radiator.

I am certain I can't dissuade you from that opinion, but what you are proposing is physically impossible.

You don't mean "improving" the closed system, you mean "restoring" the closed system. Changing to an open system doesn't "improve" anything -- the radiator has exactly the same frontal area and cools exactly the same as a "closed" system radiator of the smae type from the same manufacturer. The issue is that, after 20 years, the original radiator is probably clogged almost solid. IMHO it's a miracle it has lasted this long. I am now on the third radiator in my '88 XJ -- the original lasted 12 years, the replacement lasted 7 years. Just put in a decent new radiator and you should have no other problems.

What year did you have them check? The '86 used a smaller exhaust on the 4-cylinder. In '87 or '88 they standardized on the 2-1/4" for both engines.

It only helps at higher RPM's as it is an air flow thing. It helps get a more directed & consistent air flow to the engine so it is not really noticeable all the time on these engines. This brings to mind one other difference between the Renix and HO versiuons of the 4.0L engine -- the HO has a larger throttle body bore. That means it flows more air at higher RPMs. I don't know how the original poster drives or what RPM band he spends his time in when looking for "pep," but the smaller bore is noticeable for those who like to live in the upper end of the power band. You can but bored-out throttle bodies, or you can grab a TB from a junk yard and hone it out yourself. It might make a difference, and it's an easy, bolt-on change. (Once you get it bored out, that is.)

Sounds like someone put a 4-cylinder exhaust on your 6-cylinder truck. As commented above, unless you spend a lot of time at wide-open throttle, it won't hurt and it might help.

Nothing. There is no "Renix vacuum mess." What you may be referring to is the fact that the HVAC controls are all vacuum operated. That has nothing to do with the engine, and will remain after you swap to an HO engine. Aside from creating a lot of work for yourself for questionable gains, all you'll really be eliminating is the EGR valve.

You really can't compare the two engines. Let me repeat: You REALLY can't compare the two engines. The Renix 4.0L is a low-RPM, torque engine. The '87 was the first year for it, and it actually produced less torque and horsepower than the '88 - 90 but I still haven't found out what they tweaked in '88. However ... ... The '91 and up HO engine raised the torque peak from around 2200 RPM to well over 4000 RPM. It also changed the cam and the manifolds. The result is that the HO breathes freer and revs higher, so it feels like it has more "pep" -- because most Americans equate revving through the gears with "pep." The factory gave us what we wanted. Except for me. I prefer torque. The natural shift point for a Renix 4.0L engine is about 2,000 to 2,200 RPM. The natural shift point for an HO is around 3,500 RPM. If you want your '87 to run like an HO, you'll have to cam it.

That includes the mounting flange and fuel guage sender, so it would work. Except that your signature indicates that you own an '88, and this part is listed for the '91 & '92. I don't know if they work at the same pressure, and I don't know if the polarity is the same on the guage wiring. (Of course, the wires could be easily reversed -- they're just push-in connectors.)

Nope. It's because I've heard too many stories of the platinum electrode tip breaking off and taking out the piston. The stock plugs with the Jeep high energy ignition easily last 50,000 miles or better, so why mess around with a hand grenade in your engine? I also tried a set of SplitFires in the XJ once. Didn't run any better than standard NGKs, and gas mileage was worse. Sometimes, newer and more expensive doesn't mean "better," it just means newer and more expensive.

Go to the Monroe shocks on-line catalog. At the back they have a spec section that shows the mounting configurations, lengths, and travel dimensions for every shock they make. You can look up the stock shocks for a TJ and an MJ in the application listings and then compare dimensions. I don't think TJ shocks translate very well into the MJ, but that's based on fuzzy memory.

There is a resistance, but I don't recall what the spec is. The old FSMs used to give a number, but the new ones probably just tell you to hook it up to a scan tool. I think it was something like 1,000 ohms per inch or something like that. (Or maybe it was 1,000 ohms per foot?) Resistance is needed to reduce radio interference. Most factory wires, in fact, aren't "wires" at all. They are fibers, impregnanted with a conductive carbon compound. Over time, as the wires get hot and cold, and maybe man-handled from working around the engine, the carbon gets broken and there are gaps that the spark can't jump. That's when you start getting skipping and missing under load. The best replacement wires have a solid (or stranded) wire core, surrounded by a radio supprssion winding.

All platinums.

Have you seen this little chart for NGKs? http://www.spark-plugs.co.uk/pages/tech ... l_code.htm No. It's not an application listing, it's a chart that you use after you see what plugs fit your application, to see what type of plug the part number represents. I never had a need for that. I get them at Advanced Auto (same company as Shucks and Checker in other parts of the country) and just ask for the standard plug for a 4.0L Jeep.