Your Jeep Tech Questions Answered

Your Jeep

4.0L Engine Compatibility
My 1988 XJ engine blew a freeze plug and overheated beyond repair, and now I need a replacement engine. Would my 1996 XJ that still runs with 188,000 miles on it, but has all rusted out floorboards like a "Fred Flintstone" car, be a possible long-block donor to get the 1988 back on the road? They both have automatic transmissions.
Mark W.
Via email

You could absolutely use the engine from the 1996 Cherokee in the 1988, and there are a couple of different ways to do it. The biggest challenge you face is that the 1988 uses a Renix fuel injection system, while the 1996 uses a more modern multiport injection system. The two systems have almost nothing in common, but the engines themselves are basically the same. If the EFI in the 1988 is still functioning well, the easiest thing to do is use the Renix system on the later engine. This would require using the intake manifold, throttle body, sensors, and distributor from the old engine, which is a simple bolt-on affair. We can't think of a reason why the accessory drive system from the later engine wouldn't work in the earlier car, but if you do run into a problem, the earlier accessory brackets should bolt right to the later block.

The slightly more complicated method would involve converting the 1988 to the later MPI system. While it's quite a bit more work, the advantages are a more efficient EFI system and vastly superior diagnostics with OBD-II. To do this, you would need the complete MPI underhood engine harness, computer, and power distribution center. With a good manual, you can pare the MPI engine harness and PDC down to just what's needed to run the EFI, so all you would need to cross-connect with the 1988 harness are three wires: switched, constant, and start power. Transmission-wise, we'd recommend using the one with the later engine and retaining the transmission wiring that's connected to the engine harness, as the later computer is already set up to communicate with it. You might run into some issues trying to retain the 1988 transmission, but since the transmissions themselves are the same, you shouldn't run into any issues with fitment or compatibility with the transfer case, crossmember, or transmission mount. All things considered, we'd probably just use the Renix system on the later engine.

 

FSJ Turning Radius
I have a 1973 J4000 Jeep Pickup and a 1977 Jeep Cherokee. The steering turning ratio is awful on the pickup but acceptable on the Cherokee. Will a 1977 steering box work on the 1973? If not, what would you recommend I do? They both have power steering.
Doug B.
Via email

The turning radius of your two fullsize Jeeps is actually impacted more by the front axle than the steering box. First, have a look under the pickup, as it should have a closed-knuckle Dana 44 with drum brakes. Most resources claim that open knuckles and disc brakes came in 1974, but sources can be wrong. Jeep wasn't 100 percent consistent with its model changes, and there's always the chance that someone swapped in a later axle at some point. The best thing to do is physically look under the truck. Meanwhile, your 1977 Cherokee should have an open-knuckle Dana 44 with disc brakes. The change to an open-knuckle design and discs also reduced the turning radius from 44 to 38 feet, a substantial difference.

Assuming the pickup has a closed knuckle, there's not much you can do to improve the turning radius with the original axle. Have a look at the steering stops to see if someone adjusted them out for some reason, but that's unlikely. The best thing to do is track down a later-model Dana 44 open-knuckle front axle and put it under the truck. In addition to gaining turning radius, the change will net you much better disc brakes at the same time. The axle itself should just about bolt in, and the only other modification you will need is a later master cylinder to match the discs. Just pay attention to the position of the differential when axle shopping, as fullsize Jeeps came with both driver- and passenger-side drop axles during their production run. There should be no need to mess with the steering box, as it should have enough travel to work with the later axle.

 

Spring Bushing Slide
I recently bought a 1981 fullsize Cherokee and it's already lifted on 33s. The issue is that the rear springs seem to have shifted on the bushings. The main eye of the spring is all the way over to one side of the spring hanger and is rubbing on the hanger itself. Aside from being noisy, I don't like the metal-on-metal contact. The bushings look like they are regular rubber. What is supposed to keep the springs centered on the bushing and what do I do to fix this?
Darryl B.
Via email

Our first thought is that you should verify what kind of bushing the springs have, and also identify who manufactured the springs if you can. Aftermarket springs usually use polyurethane bushings, but some use OE-style steel-encased rubber bushings. Polyurethane bushings will usually have a light press fit in the spring eye, and there are shoulders on the bushings to keep the spring centered in the spring hanger. OE-style steel-encased rubber bushings are typically molded with an outer steel shell that has a very tight press fit into the spring eye, and it is this press fit along with a molded inner sleeve that keep the spring centered. If the bushings are polyurethane, then most likely the bushings shoulders have worn away and the bushings themselves need to be replaced. If the bushings are rubber, then either the rubber bushing itself has broken down or the spring eye has stretched a little and caused the press fit with the bushing's outer shell to loosen up.

Regardless of the cause, the fix is fairly easy with a new set of polyurethane bushings. But this is why it's important to identify the spring manufacturer if you can, because not all spring manufacturers will build springs that match the OE spring eye dimensions, meaning that a set of polyurethane stock replacement bushings may not work with your lift springs. At a minimum, you'll want to measure the diameter of the spring eyes and compare that with the dimensions of the bushings. You should also pay close attention to the poly bushing directions. Some poly manufacturers build their bushings to fit within the rubber bushing's outer shell, so you simply burn out or otherwise remove the rubber but leave the shell in place. Other manufacturers require you to remove the outer shell, and the poly bushings slide directly into the spring eye. Even if the spring eyes are stretched a little bit, the shoulders on new poly bushings should keep the springs centered and solve your problem.

 

Overheated TJ
I have a 1998 Jeep Wrangler TJ that I can't seem to keep cool. It seems to do okay in the wintertime, but as soon as the ambient temperatures start to creep up, so does the engine temp on the TJ. The engine is a stone-stock 4.0L with about 140,000 miles on it, and the Jeep is only on 33s. When it's around 100 degrees outside, the temp will run 230 just running around town without driving it hard. I've thought about adding an electric fan and an aluminum radiator. Do you think that would fix it?
Stephen E.
Via email

Cooling problems can be deceptively hard to diagnose, and it's rare for a TJ with a stock engine to run hot since they actually have a pretty big radiator and the engine compartment isn't cramped like an XJ's. Before throwing modifications at it, we'd make sure that there's not something wrong with the cooling system. Assuming there aren't any leaks and the system is full without any air bubbles, the first thing we'd check is the thermostat. It should open around 190-200 degrees F and pretty much stay open in the summer months. Carefully feel the upper radiator hose as the Jeep warms up. When it gets close to operating temp, you should feel the hose get warm rapidly when the thermostat opens, and it should stay warm once up to temperature. If the hose feels cool and the gauge is showing the Jeep is warm, then that's a sign the thermostat isn't functioning properly. Make sure the coolant in the radiator looks good and doesn't have a bunch of trash in it. Rusty water and excessive corrosion can indicate blocked passages in the radiator. If there's any doubt, flush the system thoroughly, and if there's a lot of junk in the radiator, consider having the radiator professionally rodded out. Some places will claim you can't do that with a radiator that has plastic tanks and try to sell you a new radiator, but a good radiator shop can rod out a modern radiator fairly inexpensively. Though unusual, there's a slim chance there could be something wrong with the impeller of the water pump, so it's worth having a look if everything else checks out.

We're not very big proponents of electric fans over mechanical ones, as we see and have experienced far more problems with electric fans than mechanical ones over the years. Electric fans are great solutions where space is tight or a mechanical fan just isn't feasible for one reason or another, but we wouldn't willingly replace a functioning mechanical fan with an electric one. Make sure the fan clutch is operating as it should, and make sure the factory shroud is in place. An electric fan is no match for a mechanical clutch fan with a shroud most of the time, and especially when you consider longevity. An aftermarket aluminum radiator can be beneficial, but we'd only consider using one if the stock radiator needed to be replaced. Speaking of radiators, you didn't mention if the Jeep is equipped with a winch or an aftermarket bumper, but both can reduce airflow to the radiator.

Double-check that the gauge isn't lying to you. An infrared temperature gun is handy for checking indicated temperatures against reality. If all else fails, then your overheating problem could be the result of a blown head gasket—4.0L engines are extremely robust, but they are susceptible to head gasket issues, especially if the engine has been overheated several times. If you find the head gasket is the issue, then most likely the head is warped and needs to be decked.

 

Getting Shifty
I have an NP241OR out of a 2006 TJ Rubicon that I swapped into my 1989 Jeep MJ with a Novak cable shifter and a new two-piece rear shaft. I had to pull the case from the MJ because I could not get the case to come out of four-wheel drive. Even with the cable shifter disconnected and the shift lever manually moved to 2-Hi the transfer case was still in 4-Hi. Neutral worked and 4-Lo worked but it would not come out of 4-Hi. It eventually did come out once I pulled the case from the truck. I thought it was a fluke and put the case back in only to have to same issue. I'm not really sure what the problem could be because I've never heard of anyone having the same issue with this case. Could it be something internal or maybe a driveshaft length problem that is causing the case to bind? Thanks for the help!
Ryan
Via email

If it shifts fine on the floor but not in the Jeep, our first thought is that it is an adjustment problem with the cable shifter, but it sounds like you've already checked that. It still might be worth checking again. Disconnect both driveshafts and the shifter, and then manually shift the transfer case through all the ranges using the little lever that's right on the case. If it shifts into all the ranges normally, then it's a simple adjustment problem. We've had some experience with the Novak (novak-adapt.com) cable shifter in the past and know it's a very high-quality piece, but getting it adjusted properly can take a little time. Follow the directions that came with the shifter and try again. To double-check yourself, disconnect the cable shifter and manually shift the transfer case into 2-Hi. Then put the Novak shifter in 2-Hi. When the cable is adjusted properly, the end of the cable should line up with the hole in the lever on the transfer case.

If it still won't go into 2-Hi with the transfer case installed in the Jeep but with the driveshafts and the cable shifter disconnected, make sure the little lever on the T-case isn't hitting something that's preventing it from going into 2-Hi. If that checks out, make sure the output shaft of the transmission isn't bottoming against the transfer case input and binding up the case. You didn't mention what transmission you were running, but output shaft stick-out lengths vary depending on the transmission type and model year. If all of that checks out but the transfer case won't go into two-wheel drive with the driveshafts hooked up, then there's some other problem with either the driveshafts or the axles. It seems unlikely that driveshaft lengths would be the culprit, since it would be pretty obvious when trying to hook them up to the transfer case. Lastly, though it is unusual for an NP241OR, the shift fork could be bent. The only way to check that is to crack open the case and inspect it.

 

The Right Air Source
I've recently installed ARB lockers into some 1-ton axles going under my rig, a 2002 TJ. What is the best way to supply air to them? Do I install a beltdriven compressor under the hood? An electric compressor elsewhere? Do I need an air tank? I love driving this Jeep so it won't be a trail-only vehicle (thus my reason for the air lockers). The engine has 200,000 original miles and runs great but I wonder if the beltdriven compressor would be too much for it? Any help would be much appreciated.
Brian W.
Via email

If you're only concerned about air to activate the lockers and maybe fill up a tire occasionally, the easiest thing to do is mount a small electric compressor under the hood. ARB (arbusa.com) offers three different compressors with different performance levels and price tags, and since they are designed to work with the company's Air Lockers, installation is a simple plug-and-play operation. There are many other electric compressor choices as well, with various cfm ratings and price tags to match. Running an air tank isn't necessary for just the lockers, but a tank is handy for filling up tires. The ARBs themselves don't require a whole lot of air volume or pressure, so even a small compressor is adequate if you're only worried about actuating the lockers. Note that the smallest compressor ARB offers is not intended for filling up tires. The medium-size compressor does an adequate job but doesn't really have enough capacity to fill big tires efficiently. If regular air ups are part of your plan, then we'd spring for the company's big compressor. There are multiple other compressor manufacturers, including Viair (viaircorp.com) and Smittybilt (smittybilt.com)

If you want an unlimited high-volume air source for things like running air tools and filling up big tires, it's hard to beat a beltdriven compressor. Most of the units you see in the off-road world are converted air conditioning compressors, such as a York or a Sanden. If you don't care about A/C in your Jeep, you can convert the Sanden compressor that's already on it (assuming the Jeep had A/C) into an air compressor, or you can easily add a compressor using factory parts sourced from a junkyard if your Jeep is not equipped with A/C. The mount for the compressor should already be there, so you simply need a compressor that's compatible with the mount. Converting the A/C compressor to an air compressor involves either rigging up some sort of oiling system or disassembling the compressor and greasing the bearings. There's also a fair amount of plumbing involved along with some wiring. We've detailed this process in past issues. Though a beltdriven compressor is a lot more work than wiring and plumbing an electric compressor, it's hard to beat having a portable high-volume air source. With a decent-size air tank, you can do just about anything with a beltdriven compressor that you can do with your compressor at home. Even with a lot of miles on it, your engine will be more than capable of running a compressor.